Petrol fuel injector testing (WS1)

The task that had to be done was to test the fuel injectors using the back probing method to get to the terminals so that voltages can be measured. This test was done using a multimeter and some of the tests where done whilst the engine was running and under different circumstances i.e whilst the engine was under load or at revs so that the condition of each fuel injector can be checked.

VOLTAGE SUPPLIES TO INJECTORS

The first check was to check the open circuit voltage of the battery so that you know you have enough voltage from the battery to get proper readings the voltage that we got from our battery was 12.48volts which is good enough to keep testing this reading was taken using a multimeter that is set to DCV (direct current voltage). Then we had to listen to hear that there was a tapping sound coming from each injector as this indicates whether they are operating properly and switching on and off, if there is no tapping sound then the injector may not be operating properly. The next check that was done to the petrol fuel injectors was to check the voltage going to each one, this done by back probing each terminal for each fuel injector. Then the voltage can be taken by either having ignition on but motor off, or by having the engine on idle, this check is to make sure that there is adequate voltage going to the fuel injectors. So that it is known whether each injector has enough voltage to operate properly when the injector is grounded by the transistor, when the transistor grounds the fuel injector a magnetic field is created which lifts up the pin at the end of the injector and allows for fuel to be injected into the combustion chamber. Each injector had a adequate power supply as the number one fuel injector was getting 12.30 volts, number two injector was getting 12.31volts, number 3 injector was getting 12.34 volts, and the last injector was getting 12.40 volts. This means that each injector was getting enough voltage to operate properly as they all had enough voltage to create a magnetic field that pulls open the pin for the fuel injector to allow it to open and spray fuel into the combustion chamber. If there was a reading of less than 12 volts like one of the injectors was only getting 5 volts, this could mean that there is a bad or corroded connection that is creating resistance which is using up some of the voltage to get across this bad connection, this would affect the injectors operation as now there is not enough voltage to create a strong magnetic field to pull up the pin on the fuel injector to allow the injector to spray fuel. With this weak voltage, this means that there is not enough voltage to create a strong magnetic field, however a magnetic field will be created and it might be able to pull up the injector pin a small amount this means that some fuel will be injected into the combustion chamber but that one cylinder will run a lean air/fuel mixture as not enough fuel is being injected, this could cause the engine to be down on power as one cylinder is not producing much power and the engine could run roughly as there might not be enough fuel to be ignited by the spark plug this will mean that the engine has a misfire and if its a four cylinder engine it will run on 3 cylinders this will most likely happen when the engine is under load and there is a lot more air going into the engine causing the lean air/fuel mixture and not enough fuel being injected to allow for the fuel to be ignited.

DUTY CYCLE FOR INJECTORS

The next test to be done on the injectors was checking the duty cycle of the injectors whilst at idle, these readings are taken using a multimeter that is set to duty cycle %, this test is also done by back probing the injector terminals and it has to be done with the engine at idle. The duty cycle of the injectors refers to the on time of the injectors compared to there off time, so injector number 1 was open 5.3% of the time, injector 2 was open 4.6% of the time, injector 3 was open 5.4% of the time and injector 4 was open 4.5% of the time. The injectors only need to be open for a small amount of time because when the engine is at idle there is only a small amount of air going into the combustion chamber  so there only needs to be a small amount of fuel injected to allow combustion to take place. These results are good as this means that the transistor that grounds the injector which allows it to open for the correct amount of time is in good working order, a bad result could be something like 0% or something very low this means that the injector is most likely not being grounded by the transistor and the injector will not open, so no fuel will go in to the combustion chamber and the engine will have a misfire,  this will make the engine down on power as one cylinder is not firing. Another bad result could be that the injector is grounded all the time so it is open 100% of the time this would flood the spark plug and the spark would no longer jump across the gap to ground as it is now grounding in the fuel. This means that there is no longer a spark for that cylinder and the engine will have a misfire and be down on power as there is one cylinder that is not firing, this will cause the engine to run roughly.

The next test was also done using duty cycle except this time the engine was given a quick accelerate without over revving the engine, this test was done to make sure that the injectors open for longer when the engine is under load. The engine needs more fuel when it is under acceleration as more air is going into the combustion chamber so more fuel is required to keep the power up, the ECU will make the engine run a rich air/fuel mixture whilst under acceleration to increase engine power this means that even more fuel should be injected. The results from these injectors were good as injector number 1 was open 36.2% of the time, injector number 2 was open 34.2% of the time, injector number 3 was open 31% of the time and the last injector was open 35.2% of the time. This means that the injectors opened long enough to allow for the acceleration a bad result would be one where the injector is open for a lot less time than the other injectors e.g  open 7% of the time. This would make the engine down on power or make it run roughly as there is to much air going into the combustion chamber but not enough fuel to allow combustion to take place this will make the engine run roughly and be down on power as that cylinder may not be firing due to lack of fuel. Another bad result could be that the injector is open 100% of the time the problems caused by this were explained in the paragraph above.

INJECTOR FREQUENCY

The next test was to check the Hertz (Hz) or cycles per second of the injectors whilst the engine is at idle, this test is also done by back probing each of the terminals of the fuel injectors and having the multimeter set to Hz, Hz is the frequency or number of times the fuel injector fires per second. The readings that I got for the engine was at idle all but one of the injectors fired at 9Hz the other injector fired at 10Hz, this is a good reading as this number does not need to be to high as the engine is not revving very fast only about 900RPM (revolutions per minute) so the injector does not need to fire to often. A bad reading would be one where the injector may not be firing as often as it should possibly caused by faulty signals from the ECU, this would cause the engine to run roughly intermitantly as sometimes the injector is firing and sometimes it is not firing properly this will also mean that the enigne will be down on power from time to time as one of the cylinders is not firing from time to time.

The next test was to check the Hz of the fuel injectors whilst the engine is revving at around 2500RPM, this is to see that the injectors are still firing enough times to keep the engine running smoothly. The results that our engine got was injector number 1 was 27Hz, injector 2 was 30Hz, injector 3 was 29Hz and the last injector was 28Hz. These are good readings as this indicates that the injectors are firing more often now since the engine is at increased RPM and the readings are all within close proximity to each other a bad result would be one where there is one injector where the Hz are significantly less than the other injectors, this means that the injector is firing less than what it is meant to this would cause the engine to run roughly as the one cylinder is not getting any fuel on occasional intake strokes since the injector is not firing on some intake strokes. This means the engine would intermitantly run roughly and intermitantly be down on power when that injector is not firing.

These are some of the checks that you can do, to see whether the injector is operating properly and the various tests that you can do under different engine conditions to make sure that the injector is operating properly under all circumstances.

Reference:
Petrol fuel injector image: http://www.audizine.com/gallery/data/500/fuel_injector.jpg

(WS4) Fuel Pressure and flow (petrol only)

The task that had to be done was to check the condition of the fuel pressure system on the toyota 4a-fe fuel injected motors. Checking the fuel pressure is important as this helps the fuel to get to the injector rail easily and helps the fuel to atomise when it is injected.

First the fuel pressure specifications had to be looked up for the 4a-fe motors, the fuel pressure is measured in psi for this test and the results specification for the toyota motor was 38-44psi. The next task was to install a fuel pressure gauge, however this did not apply to us as the motors already had a fuel pressure gauge installed.

The first to be done was to turn the motor to ignition, but do not turn on the motor, and check the fuel pressure which the fuel pressure was at 40 psi. This is a good reading as there is not to much pressure that could cause problems for engine running, and the fuel pressure is not to low which would mean the engine would take to long to start if it starts at all due to lack of fuel to the combustion chamber. Fuel pressure is important as it helps the fuel get to the fuel injector rail on EFI (electronic fuel injection) motors with ease and speed, but it also allows for the correct pressure and volume of fuel to injected into the combustion chamber. The fuel pressure also helps in that because it is pressurised the fuel comes out of the injectors at such force and speed that it causes the fuel to atomise which then makes it explosive and allows for combustion to take place. Fuel pressure is also needed with the engine off, this is because if the fuel pressure is allowed to drop when the engine is off, when it comes to starting the engine again the operator of the vehicle would have to turn the motor over for a long time until fuel pressure is built back up and there is enough fuel going into the combustion chamber to allow combustion to take place. However most people do not want to turn the motor over for a long time (around 10 seconds) for the motor to start so fuel is always kept under pressure when its in the fuel lines so that the vehicle starts instantly even when it has been sitting for a while.

The next test was to measure the fuel pressure when the engine is idling, this is important to know as the fuel pressure could drop with the engine running or increase to much, these would be bad results as low fuel pressure would cause the engine to run rough as the engine is running a lean air/fuel mixture. Or high fuel pressure would cause the engine to run a rich air/fuel mixture and it could cause what is known as dripping injectors where fuel pressure is so high that fuel slowly leaks past the injectors and drips into the combustion chamber this can cause a lot of unburnt fuel as the fuel is no longer atomising instead now it is a liquid and it loses its explosive properties which allows combustion to take place. The results that we got for the motor was 41 psi which is a good result as the fuel pressure is not to low and it is not to high to which these results would could cause the problems that I explained above. This results means that there is enough fuel pressure to allow the correct volume of fuel into the combustion chamber and allows the engine to run properly and efficiently.

The next test was to block the fuel return line with a clamp whilst the engine is idling, this was not done for to long as this could cause damage to the fuel system. The results that we got for the toyota motor was the fuel pressure went up to 75psi before we shut off the engine. The reason the fuel pressure went so high was because the fuel pump kept pumping the same volume of petrol to the fuel injector rail but the return fuel line which allows excess fuel to return back to the fuel tank was blocked. This meant that the fuel had no where to go, and the fuel pressure jumped up extremely high, if the engine was left running longer this would have caused damage to the fuel system of the motor as the fuel pressure would have kept increasing until something broke. With high fuel pressure in the fuel lines, this would have caused dripping injectors and a rich air/fuel mixture as when the injector opens there is so much fuel pressure that a lot more fuel comes out than what is intended and the high pressure would have caused dripping injectors causing unburnt fuel as there is so much fuel pressure that the fuel forces its way past the injector and drips into the combustion chamber and it is not atomized so it would have lost its explosive abilities and this would make the engine run roughly. If the fuel pressure remained this high it would still cause dripping injectors even when the engine was off, this would flood the motor as fuel is dripping into the combustion chamber and it would cause hard starting as fuel is not explosive, poor fuel economy as there is way to much fuel going into the combustion chamber. The high fuel pressure could also work like a choke on vehicles with carburettor's it would help during cold starts with the rich air/fuel mixture but it would hinder hot starts making the engine hard to start and could cause the engine to run roughly when it is hot since there is to much fuel to burn.

The next test was to test what happens to the fuel pressure, when the fuel pressure regulator is disconnected, the fuel pressure regulator is what sends excess fuel back to the fuel tank to maintain correct fuel pressure and help keep fuel consumption down. This fuel pressure regulator works off of engine vacuum, so it would sending more fuel back to the fuel tank when the engine is idling as there is high vacuum in the intake manifold and the engine does not need much fuel, but when the engine is under acceleration there is less vacuum so the vacuum acts less on the fuel pressure regulator as more fuel is required to keep the engine running smoothly. If the fuel pressure regulator was faulty it most likely jamb shut so it would not relieve fuel pressure this would cause the engine to run a rough air/fuel mixture. It could also cause dripping injectors. The other unlikely fault is that the fuel pressure regulator jambs open so that to much fuel is sent back to the fuel tank this would cause the engine to run a lean air/fuel mixture and could cause the engine to run roughly as there is not enough fuel in the combustion chamber to allow combustion to take place, so this would cause a misfire. The result that we got for our motor was 48psi with the fuel pressure regulator disconnected and the engine at idle. This would cause the engine to run a rich air/fuel mixture but would probably not cause dripping fuel injectors as there is not enough fuel pressure for the fuel to leak past the injectors.

With the fuel pressure regulator reconnected again and the engine allowed to run again so that normal fuel pressure can be restored. The engine was turned off and left to stand for 5 minutes then we took the residual or rest fuel pressure reading, which for the toyota motor was 42psi, this is a good result as fuel pressure is maintained for when the engine is next started. A bad result would be that the fuel pressure drops off over time this would mean that there is a fault in the fuel system that is allowing the fuel pressure to drop. This would also mean that the motor would take a long time to start as there is not enough fuel going into the combustion chamber to allow combustion to take place. The engine would only start when the fuel pressure is bought back up again, this would only happen when the engine is turning over and the fuel pump would have to build up pressure again, this means the engine would be turning over for about 10 seconds maybe longer depending on the car.

The last test to be done was to check the fuel flow so first the fuel pump was disconnected and the engine was turned over so that fuel pressure could drop to zero then the fuel line from the fuel pump was taken off and put into a beaker. Then the fuel pump was reconnected and the motor was turned over for 15 seconds, this test is done to check that the fuel pump is pumping enough fuel to the fuel injector rail. For most engines the fuel pump would pump 1/2 a litre in this time. Our engine pumped 600ml which is good result, if the fuel pump had pumped less fuel through e.g. 350ml or less this would mean that the engine would run a lean air/fuel mixture as there is not enough fuel being supplied to the engine. If the fuel pump had pumped more fuel through e.g. 750ml or more this would mean that the engine would be running rich as there is to much fuel being supplied to the fuel injector rail. These values would differ for different vehicle e.g vehicle with beg motors would pump more fuel as more fuel is required for engine operation.

These are some of the tests that can be done to check the fuel pressure system and some of the faults that occur and why correct fuel pressure is essential for engine operation.

Reference:
Fuel injector rail image (common rail diesel): http://www.commonrail.info/wp-content/uploads/2009/08/255179811.jpg

Fuel pressure gauge image: http://www.ptaaron.com/bailey/fuelpressgauge.jpg

(WS7) Exhaust gas Analysis (Petrol Only) + O2 sensors

The task that had to be done was to use an exhaust gas analyser to check the emissions of a Toyota Corsa, the type of exhaust gases being emitted can help to diagnose how the car is running and whether any tuning needs to be done to help run better. This is measured by putting a probe up the exhaust pipe so that there are no outside influences of normal air that could affect the results.

First the exhaust analyser had to be given time to take readings the surrounding air before it can take readings of emissions as the analyser needs to calibrate itself. This test takes about 30 seconds once it has done this test then the emissions can be analysed to see how the engine is running. Now the analyser probe can be put in the exhaust pipe of the vehicle that needs to be tested, the first test is to be done when the engine is cold so that the exhaust gases can be compared to under different circumstances of engine operation. The results that we got for the car was Carbon Monoxide (CO)  was at 2.5% this is high value but is expected when the engine is cold as the engine is running a rich air/fuel mixture this means that there is a lack of oxygen when the exhaust comes out as most of the oxygen has been burnt during combustion and the oxygen molecules cannot attach itself to other oxygen atoms to make Carbon Dioxide (CO2). There is a high level of HydroCarbons (HC), HC is basically unburnt fuel and helps lead to form smog, the readings that we got where 788 parts per million (ppm), this is a high number as because the engine is cold it needs to run a rich air/fuel mixture this means that there is usually to much fuel to burn and some of it condenses on the cold surfaces of the combustion chamber so the fuel does not burn, the unburnt fuel leads to high levels of HC. CO2 levels are low around 10% as there is not enough oxygen to make more CO2, the level of CO2 refers to the efficiency of combustion when CO2 gets to around 15% the engine is running as efficiently as it can as it is burning most of the fuel at this time. With some unburnt fuel this means that there is some left over oxygen (O2) because not all of the fuel was burnt and so not all of the O2 was burnt this left 5.15% O2 in the emissions. Because the engine is still running cold the ECU ignores the O2 sensor until the engine has warmed up and the car is moving at revs this is when the O2 sensor goes into closed loop and the ECU listens to the O2 sensor so that it knows whether the engine is running lean or running rich and adjusts the fuel injected to keep the fuel ratio at stoichiometric. When the engine is at idle, cold or under heavy load the O2 sensor is on open loop and the ECU does not listen to it instead the ECU uses the other sensors to adjust how much fuel is being injected. If there is a lean air/fuel mixture and the O2 sensor is on closed loop then the O2 sensor would see a high level of oxygen and it would try and richen the air/fuel mixture by injecting more fuel into the combustion chamber. If the air/fuel mixture is to rich this means that there is lack of O2 and the voltage from the O2 sensor would be high and when there is a lean mixture there is a lot of oxygen and this would cause low voltage output from the O2 sensor, the ECU uses this to richen or lean the air/fuel mixture to keep the engine running as efficiently as possible. The purpose of the O2 sensor is to reduce the amount of harmful emissions as much as possible, and to try and keep the air/fuel ratio at stoichiometry (14.7:1, the most efficient mixture that the engine can run, producing the least harmful emissions and keeping the best fuel economy). If there is to rich or to lean of a air/fuel mixture running all the time or a constant misfire, this can cause the O2 sensor to become fouled up and it would wind up giving incorrect readings to the ECU which means the ECU will think that the engine is running to rich or to lean depending on the voltage and make the engine run improperly meaning that it could run rough or have misfire, the engine could have poor fuel economy or poor performance. These faults can occur if the O2 sensor becomes fouled up with carbon from the exhaust.


^The image above shows what a good voltage wave pattern is from a O2 sensor using an oscilloscope as it shows the engine running a little bit rich then a little bit then a little bit rich again this is what causes the variations in voltage is the increasing and decreasing voltage.^


(O2 sensor)

When the engine has warmed up the next readings where taken to check how well the fuel is being burnt and how this would be making the engine run. The CO levels where at 0.001% this is because combustion is now taking place very efficiently and all of the oxygen is being burnt during combustion. HC is low and was at 37ppm this is because the air/fuel mixture is at stoichiometry or 14.7:1 when the engine is running at its most efficient. CO2 levels are at 15.16% which is normal as this means that combustion is taking place efficiently, this also shows that the car has a catalytic converter as a car that does not have a catalytic converter would never get CO2 levels as high as 15% and there would be higher levels of CO and HC without the catalytic converter. These readings are all good as it shows that there combustion is taking place efficiently and this means that there are very little harmful emissions. O2 levels are low because most of it has been burnt so the O2 level was 0.4% since there combustion burnt it all and a lot of the O2 has paired up with the CO to make CO2.

The next test was to check the emissions when the engine is revving at 2500RPM for around 30 seconds, the readings that the engine gave where that CO levels where at 0.2% which is almost nothing so it is not anything to worry about. The reason it increased a little bit is because the engine would be running a slightly richer air/fuel mixture, this means that there is a little bit more unburnt fuel as HC was at 121ppm. However CO2 levels where still at 15.10% so it means that combustion is taking place efficiently. O2 levels are lower as more fuel is being burnt which means there is more oxygen being burnt the O2 levels where at 0.3% which means all these readings are good. With the engine at revs the O2 sensor would go into closed loop and the O2 sensor would tell the ECU to adjust the amount of fuel being injected so that fuel can burn as efficiently as possible.

The next test was to run a lean air fuel mixture by creating a vacuum leak in the intake manifold this makes more air go into the engine than what the ECU thinks there is so the ECU does not add any more fuel, the vacuum leak was made by disconnecting one of the vacuum lines that recirculate exhaust gases back into the intake manifold so that they can be reburnt again. This lean air/fuel mixture has not really increased CO levels as they are still around 0.03% but HC level is high as it was at 470ppm, the HC is high because there is so much air in the combustion chamber that the fuel is not a strong enough concentration to be explosive enough for everything to burn so there is unburnt petrol. The CO2 level went down to 7.8% this is because combustion is no longer efficient as there is unburnt fuel this also results in a high O2 level of 5.9% this is because along with not all the fuel burning not all of the oxygen is burning this means that there is high level of oxygen coming out of the exhaust on the exhaust stroke. The O2 sensor would see the high level of oxygen and would try to richen the mixture if the engine is at revs, when the engine is at idle the O2 sensor is on open loop and the ECU ignores the O2 sensor.

The next test was to accelerate the engine by blipping the throttle a few times, without revving the engine to much. This creates a rich air/fuel ratio because more is going into the engine so more fuel is required but also more fuel than usual is injected as the engine needs more power to accelerate quickly. This means that there is a high level of HC at 434ppm this is because of the rich air/fuel mixture and there would be some unburnt gas, this also means there is higher CO as CO is created by a rich air/fuel mixture. CO2 is low at 10% as the engine is not running efficiently anymore this means that there is low level of O2 at 1.3% because most of the oxygen has been burnt and there is not enough oxygen for CO to turn into CO2 hence the high level of CO.

The next test was to measure what happens when a spark plug lead is disconnected, this is done by grounding the spark lead by attatching a spark tester this way voltage does not build up to much and damage the system. This test is done to see what a misfire with no spark would do to the emissions on the car, the CO levels where low as there was still unburnt fuel going into the exhaust which meant that the oxygen was not burnt this resulted in a reading of 13.6% for CO2. HC was extremely high due to the fact that one cylinder was not burning any gas this meant that HC was at 1033ppm, oxygen levels where high at 4.53% as well because of the fact that no oxygen was burnt because combustion was not taking place. Even though there is high levels of HC the oxygen sensor would see the high oxygen level in the exhaust and it would tell the ECU to richen the air/fuel mixture this would only happen if the O2 sensor was on closed loop whilst the engine is at revs, other wise whilst the engine is at idle the O2 sensor is on open loop and the ECU does not listen to the O2 sensor.

The next test was to measure the emissions when one of the injectors is disconnected so that it can be seen how this would differ from the test where no spark was taking place, now no fuel is being injected. CO levels where at 0% because there was no unburnt fuel from a rich air/fuel mixture this meant that the HC was low at 55ppm because there is no unburnt fuel however CO2 levels where lower at 11.61% because one of the cylinders is not producing any fuel this means that the engine is not running as efficiently as it could this also means that there is a high level of O2 at 5.45% because no oxygen is being burnt due to the fact that there is no fuel to let the oxygen burn this means that there is high level of O2 during the exhaust stoke. The O2 sensor would see the high level of oxygen and try to richen the air/fuel mixture as it would think that the engine is running to lean.

These are the results that you can expect to get when the engine is giving put under different conditions and the level of the different emissions the engine will produce from these different running conditions.





Reference:

Exhaust analyses on car image-http://www.google.co.nz/imgres?imgurl=http://www2.le.ac.uk/departments/engineering/people/academic-staff/aldo-rona/research/technology-development/internal-combustion-engines/liquid-petroleum-gas-lpg-conversion-of-a-1600cc-car-engine/11.gif/image_preview&imgrefurl=http://www2.le.ac.uk/departments/engineering/people/academic-staff/aldo-rona/research/technology-development/internal-combustion-engines/liquid-petroleum-gas-lpg-conversion-of-a-1600cc-car-engine/commissioning-and-testing-a-liquid-petroleum-gas-fuel-system&usg=__0C8FFcaiEOrdRFO9zU-qjitGnAQ=&h=261&w=400&sz=176&hl=en&start=603&zoom=1&tbnid=eu20S7Groi7cIM:&tbnh=119&tbnw=165&ei=y-4YTqzgJsrHmAWb1cgT&prev=/search%3Fq%3Dexhaust%2Bgas%2Banalyzer%26hl%3Den%26biw%3D1280%26bih%3D711%26gbv%3D2%26tbm%3Disch&chk=sbg&itbs=1&iact=hc&vpx=484&vpy=248&dur=552&hovh=119&hovw=165&tx=139&ty=84&page=23&ndsp=25&ved=1t:429,r:8,s:603&biw=1280&bih=711

O2 sensor image: http://www.airpowersystems.com/corvette/c5/install/lhs_front_o2_sensor.jpg

Oscilloscope wave pattern : http://www.4x4wire.com/toyota/4Runner/tech/OBDII_ECU/o2_sensor_frequency.jpg

Inputs and outputs using an ocsiloscope

The task that had to be done was to check the inputs and outputs of the ECU and see the voltage wave forms that are created using an occiloscope. This test is much like testing the sensors using a multimeter except instead of checking voltages now voltage wave forms can be used, this tool can give a much more accurate depiction of what a sensor is doing by monitoring the wave forms that a certain sensor produces.

Testing Throttle Position Sensor

The first sensor wave pattern that was tested was the TPS (Throttle Position Sensor) this was tested to see whether there is a flat spot during acceleration that could cause the engine to run rough as the engine is running a lean air/fuel mixture. This is because the TPS is telling the ECU that the throttle is open less than it actually is so less fuel is going into the combustion chamber. The TPS is used so that the ECU can estimate how much air is going into the engine and therefore adjust how much fuel is injected into the combustion chamber.

To test the TPS and other sensors we used the boards that are wired up to each sensor and then place the probes for the multimeter or oscilloscope into the tester connections for the individual sensors, however in the real world there are no boards to use to test each sensor, so back probing is used. This is where a small metal pin or something similar to a pin that is used to slide down the side of a wire and goes down and touches the terminals of the connector for that sensor, this is done so that no damage occurs to the wire or connectors but allows for testing to take place.

Problems that can occur are flat spots in the TPS that mean the engine could run lean. Another fault that could occur is that the TPS gives to high voltage when the engine is at low RPM's or idle this would mean that the engine would run a rich air/fuel mixture, this is because the ECU believes the engine is under acceleration or the throttle is more open than what it actually is so the ECU thinks there is more air going into the engine, this could make the engine run roughly if there is to much fuel going into the combustion chamber and the fuel could flood the spark plug causing the spark to go through the fuel and jump across the gap to earth, this would mean that the engine would misfire and run roughly and there would be a lot of unburnt gas going out the exhaust creating high exhaust emissions. These are some of the problems that can occur with the TPS and how it would affect engine running and how you can test the TPS using the back probing method.

MAP Sensor

The next sensor to be tested using the oscilloscope is the MAP (Manifold Absolute Pressure) sensor, this is used to check how the voltage behaves in relation to the air pressure in the intake manifold so that it is known whether the MAP sensor is sending the correct signals to the ECU, this means that as the throttle opens up more air pressure will increase so voltage from the MAP sensor should increase, this is another method used with the TPS so that the ECU knows how much air is going into the engine. So when the engine is at idle the sensor should be sending a small voltage to the ECU but as the throttle is opened up more the air pressure should increase and therefore the voltage from the ECU should increase as well. When the throttle is closed suddenly the voltage should drop down quickly as air pressure decreases quickly then the voltage should drop below idle voltage then return to normal idle voltage this drop below idle voltage is because the throttle is now closed but the engine still is revving this means that air is still rushing into the engine quicker than what air pressure can restore behind the throttle valve so there is a greater increase in vacuum and a greater decrease in air pressure temporarily than what it is at idle.


A MAP sensor can be tested by setting a mulitmeter to DCV (direct current voltage) and can be checked using the back probing method to test how a sensor is operating by reading its voltage outputs to the ECU. But an oscilliscope can also be used to see how the voltage wave patterns behave to get a more accurate reading of what signals the MAP sensor is sending to the ECU, this can also be checked by using back probing to check the sensors condition.

If there is a problem with the MAP sensor in that it could be sending to low of a voltage to the ECU because it could be blocked up with dust and other materials that are entering the throttle body, this will mean the MAP sensor gives the wrong information to the ECU and the MAP sensor is telling the ECU that there is less air going into the engine than what there actually is. This means that the engine will be running a lean air/fuel mixture this could mean that the engine will run roughly and could as there is to much air this could cause pinking or detonation this is when combustion takes place before it is meant to and causes a knocking sound mostly when the engine is under load and this could put holes in pistons as the combustion is not taking place smoothly and pushing down on the piston instead pinking or more so detonation is like hitting the piston with a hammer and it the combustion takes place to early so the flame front hits the piston as it is still coming up on its compression stroke. This is how damage can occur to the motor and the engine will be lacking power with the leaner air/fuel ratio. The MAP sensor could send to high of a voltage to the ECU this would make the ECU think that more air is going into the combustion chamber than what actually is this would mean the ECU would inject more fuel into the combustion chamber and there would be a rich air/fuel mixture this would cause an increase in power but a decrease in fuel economy. These are some of the problems that can occur with a faulty MAP sensor.

Crankshaft (RPM) Sensor

The next sensor to be tested using the ocsiloscope is the crank shaft sensor which is located in the distributor this sensor is also known as an RPM sensor, the purpose of the crankshaft sensor is note engine speed and crankshaft rotation so that the ECU can know which stroke a piston is on so that fuel can be injected and the spark can be created at the correct time to allow combustion to take place. The sensor works by spinning iron passed a magnet the spinning part of the sensor is known as the reluctant and has 4 iron pieces attached to it at even intervals there are 4 pieces of iron as there are 4 cylinders there is one piece of iron for each cylinder. The iron spins past a stationary magnet and as it spins passed a magnetic field is created and voltage is induced to the magnet which has a winding of fine wire around it. Voltage will drop below zero at a time this is because there is a change in polarity, there is also a point where no voltage is induced as the magnetic lines become parallel and the magnetic lines have no affect and therefore no current can be induced into the winding. The ECU measures the frequency of this wave form to calculate engine speed so that fuel injectors can opened at the correct time and a spark can be created at the spark plug at the correct time.

This sensor can only be accurately checked using a oscilloscope as a multimeters refresh rate is to slow to show any correct readings. The crankshaft sensor can also be checked using the back probing method and setting up the oscilloscope making sure that the volt divisions are about 1 volt and the time per division is around 20 milliseconds as these wave formations occur very quickly and if the time divisions are to long then an accurate reading cannot be sourced.

If a problem occurs with the crankshaft sensor then the engine will most likely not start as the ECU does not know what stroke the engine is on and it therefore cannot open fuel injectors at the correct time nor can it fire the spark plugs at the correct time. So the ECU will most likely not fire the injectors or the spark plugs and the engine simply will not start. This is the only affect of operation that a faulty crankshaft sensor will have as the sensor will most likely send no information to the ECU.

Fuel Injector Testing

The next component to be tested using an ocsilloscope is an output from the ECU and it is the fuel injector. The fuel injector works by using a transistor to ground the circuit so that current can flow to ground this means that current flows through a magnetic winding which pulls up a small pin on the end of the fuel injector and fuel sprays out into the combustion chamber, then the transistor is ungrounded the magnetic field collapses and the pin moves back up and the fuel injector is off again and no fuel is being sprayed into the combustion chamber.

The wave pattern that occurs with a fuel injector is one where there is an initially high voltage of around 12volts when the voltage suddenly drops away to zero the the transistor has grounded the circuit and the voltage is therefore being used up to open the injector, when the injector shuts off the voltage increases above 12volts in a voltage spike this is because a magnetic field was created to lift up the pin that opens the fuel injector that allows fuel passed the injector when the circuit is suddenly shut off the magnetic field collapses the collapsing magnetic field induces current and creates a voltage spike.


Problems that can occur with fuel injectors are faulty transistors that mean that the injector cannot ground properly i.e a transistor that grounds the fuel injector the entire time so that it could be on 100% of the time and so it therefore never stops spraying fuel into the combustion chamber. Or the transistor does not ground the fuel injector and it therefore never sprays fuel into the combustion chamber. Other faults that can occur with fuel injectors are blocked injectors which that there is not enough fuel getting into the combustion chamber.

These are some of the diagnostics you can do using an oscilloscope to measure the wave patterns of the sensors and outputs of the ECU to see whether they are in good condition or not.




Reference:
 Image of Back Probing :  http://www.google.co.nz/imgres?imgurl=http://www.crownvic.net/ubbthreads/ubbthreads.php%3Fubb%3Ddownload%26Number%3D18221%26filename%3DMAF%2520voltage%2520measured.jpg&imgrefurl=http://www.crownvic.net/ubbthreads/ubbthreads.php%3Fubb%3Dshowflat%26Number%3D2086626&usg=__Lpv1EZIlASdhiGAiuDlFzLfkdaY=&h=480&w=640&sz=87&hl=en&start=154&zoom=1&tbnid=r0Gh8Gicn-f4yM:&tbnh=124&tbnw=167&ei=gSkNTtvbNKyNmQWHr83iBw&prev=/search%3Fq%3Dback%2Bprobing%2Bsensors%26um%3D1%26hl%3Den%26sa%3DN%26biw%3D1024%26bih%3D574%26tbm%3Disch&um=1&itbs=1&iact=rc&dur=330&page=11&ndsp=15&ved=1t:429,r:10,s:154&tx=32&ty=37

image for map sensor wave form : http://www.picoauto.com/waveforms/images/zoom/map_sensor_analog.png

Image of TPS waveform : http://www.aa1car.com/library/tps_waveform.gif

Image of crankshaft sensor waveform : http://www.picoauto.com/waveforms/images/zoom/crankshaft_sensor_inductive_cranking.png

Image of fuel injector waveform : http://thm-a04.yimg.com/nimage/76fed3dafc2b29e4

(WS2) Flash Codes

The task that had to be done was to create a fault with one of the sensors on the engine so that the ECU would log that there is a fault with the the engine. Then we had to bring up the flash codes by checking what sequence the check engine light flashed its codes so that the fault can be found. Fault codes can only be brought up on cars that are EFI (electronic fuel injection) and that have ECU's so that the code can be filed, you could not check fault codes on a car with a carburettor.

A flash code is a fault that is stored in the ECU that the ECU then brings up the check engine light on the dash board. Then you can bring up a flash code, in which the check engine light will flash a certain amount of times this reveals the number of the fault logged in the ECU, you can then bring up the code by. Turning the engine off, then turn the key to ignition then off, then switch it to ignition again, then off, then bring it to ignition again, the codes will begin to flash on the check engine light. The sequence in which the light will flash is it will flash out first number to its value e.g. 3 so the light will flash three times then pause then flash out the second number of the code e.g. 5 so the check engine light will then flash five times so the fault code is 35. Then you would check the manual to see what the code 35 refers to which sensor or which component is giving abnormal readings to the ECU for that code to be logged. Note that there can be multiple fault codes so there could be another pause after 35 and another flash code is given.

Fixing a problem could be as simple as reconnecting a loose terminal however in most cases the part that is giving fault would have to be replaced for example fault code 35 could refer to the TPS (throttle position sensor) and that would have to be replaced. However the other problem could be a faulty wiring within the system so replacing the sensor would not fix anything, this is the many problems that is faced with diagnoses as the ECU tells what sensor or component the fault is with but it cannot tell whether the fault is with the sensor or the connections to that sensor. But before going and checking the whole electrical system or replacing the sensor check the condition of the wires/insulators and terminals for that sensor and see whether they have any corrosion, and check that all the terminals are still connected.

To clear the fault codes you disconnect the battery or the main engine fuse for 30 seconds as this wipes the memory in the ECU then you can reconnect back together. Then check that the codes have been cleared by turning the engine back on and check that the check engine light does not come back on. If it does not come back on then the fault has been successfully fixed. Faults with sensors could cause the engine to run roughly and lower engine performance as the ECU is not getting correct signals from the sensors and this one fault could possibly create other faults that are not filed by the ECU that could make the engine run roughly. After fixing the problem check that all the voltages are within manufacturers specification on all the sensors that where faulty. This is to make sure that the ECU is still correct signals from the ECU and that it will not log another fault.

This how you can bring fault codes on cars with ECU's and the checks that you can do fix the problems and how the codes are cleared after the problem has been fixed so that the check engine does not remain on.



Reference: http://www.gtfours.co.uk/what/fcd/check_eng.jpg (check engine light image)

Inputs and outputs using the multimeter

The task that had to be done was to test and check the condition of the sensors on a electronically fuel injected toyota motor. Before the tests took place the oil level and coolant had to be checked before the motor started, this is done to ensure that no damage occurs to the engine.

INPUTS

Inputs are the signals from sensors all around the engine that the ECU relies on to keep the engine efficiently and smoothly.  

TPS testing

The first sensor tested was the TPS (throttle position sensor) this test is done with engine off but ignition on the sensor was tested by placing the multimeter probes onto the board that allowed us to get readings from the different sensors on the motor, but in real life this cannot be done so you can use the back probing method to get readings from sensors(more information on back probing can be got from the inputs and outputs using oscilloscope post), this was the method to how each of the sensors was tested .First the throttle was tested when it was closed or at the idle position, it gave a reading of 0.5 volts then the throttle was opened up fully and the sensor gave a reading of 3.9 volts it was tested by setting the multimeter to DCV (direct current voltage). The TPS sends the voltage to the ECU (electronic control unit) as a signal this tells the ECU how open the throttle is and therefore it can estimate much air could be going into the motor and adjust the fuel injected into the combustion chamber correspondently to keep the air/fuel ratio at stoichiometric mixture which is 14.7:1 or 14.7 parts of air to one part of fuel. Stoichiometric must be kept as this is usually the most efficient ratio for the motor to run on. The greater voltage or signal that the ECU receives the more fuel the ECU keeps the fuel injectors open to keep the correct air/fuel ratio. If the TPS is faulty i.e. there is flat spot where bad contact is being made, this could also be a voltage decrease as the throttle is opened more instead of the normal increase in voltage that is sent to the ECU. This means the TPS tells the ECU that the throttle is open less than what it actually is this could cause a power lag as the air/fuel mixture would be to lean because not enough fuel is being injected into the combustion chamber and the engine would be down on power for a brief moment. The throttle position sensor is located on the opposite side of the air intake to the throttle control.

COOLANT TEMP SENSOR

The next was done when the engine was running but this is done immediately when it is cold so that it can compared with when the engine was warm. This test was on the coolant temperature sensor, when the engine or coolant is cold the sensor sends 2.5 volts to the ECU and when the engine has warmed up this sensor was tested by setting the Multimeter to DCV, the sensor sends 0.5 volts to the ECU the greater voltage is sent to the ECU when the engine is cold so that the ECU knows what temperature the engine is and therefore whether the engine needs a rich air/fuel mixture when it is cold. The engine needs a rich air/fuel mixture when it is cold as fuel condenses on the cold surfaces of the combustion chamber and the fuel loses its explosive abilities when it condenses back to a luquid, a rich air/fuel mixture would be 12:1 or less. So more fuel is injected into the combustion chamber so that there is still enough fuel to keep the engine running when it is cold. Once the engine has warmed up the coolant temperature sends less voltage to the ECU this is so that the ECU knows that the engine has warmed up and not as much fuel needs to be injected now because the fuel cannot condense on the hot combustion chamber walls and now less fuel is required to keep the engine running as none of it is condensing and all of it can combust. If there is something wrong with the coolant temp. sensor then the ECU does not know whether the engine is cold or warm and cannot give the correct air/fuel ratio this could cause the engine to run rough as it the engine could run to lean and fuel won't be as combustible. A lean air/fuel mixture would be 17:1 or more. If the coolant temperature sensor is not working properly i.e it is sending to high of a voltage to the ECU when it has warmed up, then the ECU thinks that the temperature in the engine is less than what it actually is and the ECU will open the fuel injectors for a longer period of time and a rich air/fuel mixture is created. This would cause an increase in power but a decrease in fuel economy as more fuel is being injected than what is needed. If the coolant temperature sensor sends to low of a voltage to the ECU then the ECU thinks the engine is warmer than it actually is this could cause the engine to run roughly when it is cold and a lot of the fuel is condensing on the cold surfaces of the combustion chamber but this should become better as the engine warms up.

RPM sensor

The next test was to check the crank shaft and cam shaft sensors otherwise known as an RPM sensor as these sensors are usually located in the distributor of cars that have ECU's but do not have coil over plug arrangements, these sensors are usually tested by setting the multimeter to ACV (alternating current voltage) or it can be measured by setting the multimeter to Hertz (Hz) or cycles per second then checking both the crank shaft sensor and the cam shaft sensor whilst the engine is running. Then check the Hz (hertz) for the two sensors by setting the multimeter to Hz. The crankshaft and camshaft sensors purpose to let the engine ECU know at what point the engine is so that it knows when to fire the spark plugs and the fuel injectors. The ECU measures the frequency or Hz of that the sensor is putting out to know what the engine speed is or by how much the engine is revving so that fuel injectors can be opened at the correct time and the spark can occur at the correct time. At idle the crankshaft sensor should read about 0.8v(ac) and the camshaft 0.25v (ac), and the Hz should be about 37Hz for the crankshaft sensor at idle and 80Hz at 2500RPM and at idle the camshaft sensor should be 20Hz it shouldn't increase to much more when the engine  is at revs. If either the crankshaft sensor or the camshaft sensor fail then the engine will not run because these sensors tell the engine where the crankshaft is located or piston position, and the camshaft sensor tells the ECU what stroke the cylinder is on whether it be intake, compression, power or exhaust. This sensor lets the ECU know when to inject fuel and when to fire the spark plugs if the arrangement is coil over plug. Usually when a RPM sensor becomes faulty it does not send any voltage to the ECU so the ECU does not know that the engine is trying to started and the engine therefore will not start nor will it run as the ECU does no know when to fire fuel injectors or the spark plugs.

MAP sensor

The next sensor to be tested was the MAP (Manifold Absolute Pressure) sensor this was tested by having the multimeter set to DCV, this sensor measures the vacuum in the intake manifold. Vacuum is a low pressure zone this is caused when the engine is running at low RPM's and the throttle is closed or near closed air is being forced away into the engine as the air rushes into the engine but there is not enough of it going back into the intake manifold to keep equal pressure. When the engine is at idle the voltage from the MAP sensor should be quite low as air pressure in the manifold is low but vacuum should be very high on the toyota 4a-fe motors the voltage is around 1.5 volts when it is at idle. The voltage should increase as the throttle opens up more and air pressure in the intake manifold increases or as vacuum decreases. With the engine off but the key on ignition the voltage is around 3.6volts this is because air pressure is now equal to what it is outside so the MAP sensor is telling the ECU that there is high air pressure in the intake manifold which would mean the throttle must opened up and if the car was running then the ECU would make the fuel injectors open for a longer period of time. The MAP sensor tells the ECU how much air is going into the engine and it can then control how much fuel is injected into the combustion chamber to keep the correct air/fuel ratio. If the MAP sensor becomes faulty then the ECU does not know how much air is actually going into the engine, so depending on the voltage that the MAP sensor sends to the ECU will determine whether the engine could run a lean air/fuel mixture or a rich mixture. For example if the MAP sensor was sending to low of a voltage to the ECU then the ECU would think that the engine has less air going into the combustion chamber than what there actually is this would mean that the ECU would inject less fuel this would create a lean air/fuel mixture and the engine would be down on power and could run roughly as the fuel loses sum of its explosive abilities, a lower reading could be caused by a sensor that is blocked up with sludge that can build up in the intake manifold. If there was a higher reading caused by a faulty MAP sensor then the ECU would think that there is more air going into the engine so it would increase the fuel injected into the combustion chamber this would cause a richer air/fuel mixture the engine would have greater power but it would also have greater fuel consumption.

AIR TEMP SENSOR

The last sensor to be checked was the air temperature sensor this was tested by having the multimeter set to DCV, first it must be checked when the engine is cold which should be around 2.5 volts or more if the outside air is relatively warm and decrease to 2.3 volts or less when the engine has warmed up. The purpose of the air temp. sensor is to let the ECU know the temperature of the air going into the engine, this is because during cold conditions air is much more dense and therefore more fuel is required to keep the correct air/fuel ratio, however in hot conditions air is less dense and becuase there is less air, less fuel is required to be injected to keep the correct air/fuel ratio. If the air temp. sensor does not work then the ECU does not know how dense the air is and will not know how much fuel to inject into the combustion chamber. However this is not such a big problem as the difference between hot and cold conditions and the fuel required is so small it would not have much affect on the operation of the motor. A faulty air temp sensor could make the engine less efficient or make it lack power but it wont affect engine operation to badly this is just because it does not know whether to add more fuel or less fuel to keep the correct air/fuel ratio.

OUTPUTS

Outputs are what the ECU controls based on what it recieves from its input sensors.

FUEL INJECTOR TESTING

The next test was to measure the fuel injector cycle which is an output from the ECU, this is done by setting the multimeter to duty cycle % and setting it to the negative voltage, with the engine and at idle the reading should about 5%, that is the fuel injector is only 5% of the time as only a small amount of fuel is required to keep the engine running, however when the engine is under acceleration the injectors on time should increase to about 15% depending on how much acceleration is required as more fuel is required to help the engine accelerate and increase its revs. The purpose of the fuel injector is to inject fuel into the combustion chamber at the correct time with the correct amount of fuel being injected to allow the correct air/fuel ratio to be kept under different conditions. The percentage is the on time of the injector compared to its off time. Faults that could occur with fuel injectors that stop normal operation are faulty connections that could stop the injector from firing. This could cause the engine to run rough as one cylinder is not firing, or the injector could be on 100% of the time this would also cause the engine to run roughly as the spark plug would become flooded with petrol and would not spark but also the air/fuel ratio would be so rich that plug would not be able to ignite the mixture. The main problem of an injector not working properly would be the transistor that grounds the circuit so that the injector spray tip can open when a magnetic field is created as the transistor is what makes the fuel injector work properly when a circuit is created.

IDLE AIR CONTROL

The last test was the Idle Air Control sensor, the idle air control sensor regulates the engines idle speed by adjusting how much air is allowed passed the closed throttle valve, the ECU can control the idle speed by signals from other sensors. Like when the engine is cold and it needs to rev a bit higher more air is allowed passed the closed throttle valve to let the engine rev more so that it does not stall. The idle air control sensor can be checked by setting the multimeter to duty cycle % and setting it to negative voltage the meter should read about 35% when the engine is idling. A faulty idle air control sensor would mean that the ECU does not know how much air is being let passed the closed throttle valve this could cause uneven idling of the motor however the motor should return to normal operation when at revs or under load.

COIL OVER PLUG TESTING

Another output from the ECU that can be tested but didn't show in the sheet is testing coils. This can only be done on coil over plug motors, to test this set the multimeter to duty cycle % and set it to positive voltage as this measures when it sparks. The reading at idle should be about 3% on time compared to off time, this number should not change when the engine is revving as spark duration does not need to change to effectively ignite the air/fuel mixture in the combustion chamber. The reason that manufacturers went to coil over plug arrangements is that now one coil controls one cylinder where as before one coil controlled multiple cylinders. This means that coil gets more time to charge up and create a strong magnetic field so that when the magnetic field collapses a stronger spark is created. When there was just one coil that is creating a spark for multiple cylinder it cannot not effectively create a strong spark at higher revs because the coil does not have enough time to charge up enough to create a strong spark, so the main benefit of coil over plug is that strong sparks can still be created at high rpm and engines will not lose any power as one coil has enough time to create a strong spark no mattter what the revs are. Faults that could occur are the coils could become worn out and the spark might not be created this would cause the engine to run roughly as the engine would not be firing on all cylinders.



These are some of the basic tests that you can do to check the condition of some of the sensors in an electronically fuel injected motor which in my case was a toyota 4a-fe. And what some faults with the sensors could mean for the operation of the motor.





TPS Image:
http://www4.wave.co.nz/~lakewood/Skyline/ThrottlePositionSensor.jpg

Coolant temp sensor image: http://i37.photobucket.com/albums/e66/das2123/Neon%20Sensor%20Locations/CoolantTempSensorSOHC.jpg

Crankshaft sensor image: http://i288.photobucket.com/albums/ll187/90BlueXJ/Jeep%20assembly/Crankshaft_Position_Sensor_diagram.jpg

MAP sensor image:
http://www.handen.us/caprice/map.gif

Air Temp. sensor image:
http://www.v8sho.com/SHO/images/iatsensor.gif

Fuel Injector Image:
http://www.audizine.com/gallery/data/500/fuel_injector.jpg

Coil Over Plug image:
http://i200.photobucket.com/albums/aa76/shutterflick/IMG_5644.jpg

Idle Air Control Sensor and other sensors image:
http://www.domesticcrew.com/images/parts4.jpg