Diagnostics (Post 3)

WS4 FUEL PRESSURE AND FLOW (PETROL ONLY)

The task to be done was to check the fuel pressure in the fuel rail on a toyota 4A-FE motor, this is done to make sure that everything is working properly so that the correct amount of fuel is delivered to the motor. These techniques can be used in engine diagnosis.

The first task to be done was to attach a fuel pressure gauge, but since a fuel pressure gauge was already installed this step was not necessary. Next the fuel pressure in the fuel rail had to be measured with the engine off, the reading I got was 35 PSI, the reason that pressure is needed in the fuel when the engine is off, is so that the engine starts quickly after its been at rest, and so that the engine does not need to be cranked over for a long time to build up the pressure again so that it can start. The reading of 35 PSI is a good reading as this is a good pressure to allow the fuel to atomize properly when it is injected into the combustion chamber. A bad reading would be a low reading something lower than 20 PSI this could indicate a fault with the fuel pressure regulator allowing to much fuel past suggesting that it is not shutting off the fuel return line completely when there is no vacuum being applied and this would cause the fuel pressure to drop.

http://www.rx7.org/Robinette/images/fuel_gauge.gif

Next the fuel pressure was measured with the engine on but at Idle, the reading I got was 38 PSI which is a good reading as the pressure has increased, as now fuel demand is needed and higher pressure is required for fuel atomization. A bad reading would be anything less than 25 PSI this could be caused by a faulty fuel pump which is not pumping enough fuel to maintain correct fuel pressure. Or a faulty fuel pressure regulator which would cause the same problems as with the engine off fuel pressure test above.

The next test was to measure the maximum fuel pressure that can be attained, this is only done for a brief moment as damage can occur if its done to long. To attain maximum fuel pressure a clamp is used to clamp the fuel return line this is done make sure that the fuel pump is working properly and to check whether there are any leaks. The reading I got was 80 PSI which is a good reading, the fuel pressure rapidly increased to 80 PSI, this indicates that everything is working as it should. A bad reading would be one where the fuel pressure does not increase rapidly indicating a problem with either the fuel pump or the fuel pressure regulator.

The next test was to measure the fuel pressure at full throttle this is done by disconnecting the vacuum line to the fuel pressure regulator. This partially closes the fuel return line so that some fuel can return to the fuel tank but allows fuel pressure to increase since fuel demand is higher and the same fuel pressure as Idle would not be enough fuel under full throttle conditions meaning that the engine is running lean and it would be lacking in power. The reading I got was 48 PSI which is a good reading as fuel pressure has not increased to much but enough to allow the engine to keep running smoothly. Then reconnect the vacuum line after the test has been completed.

The last test was to measure the residual fuel pressure, this is done by switching off the engine for 5 minutes then taking the reading. The reading I got after 5 minutes was 42 PSI this is a good reading as the fuel pressure does increase slowly for a while then after a few hours it will slowly decrease. A bad reading would be anything under 25 PSI after 5 minutes as this could indicate that the fuel pressure regulator is faulty and is not maintaining correct fuel pressure after the engine has been switched off.

This is one of the main ways that you can check that the fuel system of the car is working properly.

The last part of the test was to answer some questions.

1) Explain why it is important to know a vehicles fuel pressure/flow?

-It is important to know a vehicles fuel pressure as correct fuel pressure is needed to allow for the correct amount of fuel to be injected into the combustion chamber. To much fuel pressure would mean that to much fuel is being injected and the engine would be running rich causing increased fuel consumption, if the fuel pressure was way to high like 80 PSI in the max pressure test that would cause what is known as dripping injectors. This is when the fuel pressure is so high that the fuel drops down in droplets and does not atomize properly causing a lot of unburnt fuel, also when the engine is off the fuel could drip past the injectors meaning that the engine is hard to start since it has essentially flooded itself. If the fuel pressure was to low then the engine would run lean making it lack in power and possibly run roughly.

2)Describe the symptoms a vehicle would give with each case.

LOW FUEL PRESSURE: The engine would run lean as it is not getting enough fuel, it may not idle properly and the revs could be to low due to there not being enough fuel to combust and this could cause the engine to run roughly during acceleration as there is not enough fuel to allow combustion to take place properly.

LOW FUEL FLOW: Could be caused by a faulty fuel pump which is not pumping enough fuel, this may not have any affect at Idle as there is enough fuel but as engine load and revs increase there is not enough fuel for the engine and this could cause to run rough as there is not enough fuel to efficiently combust.

HIGH FUEL PRESSURE: Fuel pressure regulator could be faulty causing dripping injectors if it is pressurizing the system to highly otherwise the engine would always be running rich causing increased fuel consumption.

FAULTY FUEL PRESSURE REGULATOR: Can cause dripping injectors which can cause hard starting since the motor has essentially flooded itself as fuel could get past the fuel injectors when the engine is off. Fuel could leak into the intake manifold causing a rich mixture. This could help during cold starts like a choke but hinder the ability for hot starts.

FLASH CODES (WS2)

The task to be done was to bring up what is known as flash codes, this is when the check engine light will flash in different amounts of time to bring up a number which is related to a sensor. For example the check engine light could flash 3 times then pause then flash another 5 times, this would relate to the code 35 which would then be checked against that vehicles manual to see what sensor the code relates to.

http://codinghorror.typepad.com/.a/6a0120a85dcdae970b0128776ffac2970c-pi

The vehicle that I bought up the flash codes on was a 1997 Mitsubishi Legnum, to bring up the flash codes the pin 1 on the DLC (Data Link Connector) had to be earthed out using an earthing wire which was earthed onto the chassis of the car then to the key to ignition. The DLC was located under the steering wheel but this varies for different cars some can be found under the bonnet or on the passenger side.

Once pin 1 on the DLC had been earthed out the flash code that I got was 23 which was the camshaft position sensor. After doing a visual inspection of the camshaft position sensor I found that there was a grease build up on the connector which would cause a weak signal to be sent to the ECU, after the grease and dirt was cleaned off of the sensor and connector, the engine was started and the check engine light went out indicating that the voltages sent to the ECU where now fine. This meant that the fault had been fixed.

To clear the codes the battery was disconnected for 30 seconds, this discharges the capacitors and wipes the memory of any codes in the ECU. Once this has been done the system was rechecked for codes by earthing out pin 1 on the DLC. There where no codes in the ECU which was indicated by the check engine light flashing continuously indicating no codes.

The faulty camshaft position sensor would have affected engine operation by the engine missing intermittently as it does not know when to fire the fuel injectors or the spark plugs so the ECU does not fire them until it gets a signal. If the sensor was really bad and sent no voltage to the ECU, the engine would start as the ECU would not know when to fire the injectors or the spark plugs.

Once the fault codes have been cleared, other sensors should be checked to make sure that other faulty sensors are causing problems that the ECU is not logging as a fault, this could include testing the throttle position sensor, or the air flow/pressure sensors. Anything that could cause the engine to intermittently miss or run rough.

This is one of the ways that you can check the engine for faults.

SCAN TOOLS (WS5)

The task to be done was to check for fault codes logged on the ECU using a scan tool. A scan tool is a tool which reads the codes on the ECU and tells you exactly what component has been logged as a fault. The scan tool can also give live data feed, this is where it tells you exactly what voltage or reading different sensors are getting, what the engine rpm is doing and many other things which is very useful for engine diagnostics.

The first thing to do was to select the vehicle that you wanted to scan, the selection of vehicles is given to you before you do anything else with the scan tool in my case I selected Mitsubishi.

http://ts2.mm.bing.net/images/thumbnail.aspx?q=1264315473165&id=84dd3886fd892782beb0046c2b46c13a

The live data feed on the scan tool gave me the following data for my 1997 Mitsubishi Legnum when the engine is at idle.

PID=Parameter Identification          Letters to describe       Value of Data      Units of data

Engine load                                           MAF                              1.33                        volts 

Engine RPM                                         crank sensor                    968                       RPM

Throttle Angle                                       TPS                                624                       milli volts

engine coolant temp.                             ECT                                71                         degrees celcius

intake air temp.                                     IAT                                  26                        degrees celcuis

Fuel injection opening pulse                 Injector                             0.5                        milli seconds

Transmission select position                 Manual gearbox                neutral                  N/A

Vehicle Speed                                                                            0                           km/h

oxygen sensor                                    02S                                  703                       millivolts

Idle control                                        IAC                                  41                        duty cycle

barometric pressure                          pressure sensor                 99.0                      kPa



This live data feed is very useful in engine diagnostics as it allows for you to look at many different sensor outputs at one time, and look for a problem which may be affecting other sensors outputs. The live feed also saves time against checking each individual sensor to try and find a problem. However Parameters or specifications are needed when using the live data feed or else all the information would mean nothing as you need specifications to make sure that each sensor matches this and that the sensors are not giving incorrect readings.

After the live data feed results had been checked it was time to check the ECU for trouble or faults codes, this is done by selecting the diagnosis or scan part of the scan tool, the scan tool then reads the ECU and brings up the code which was 23 and the component which was the camshaft position sensor, this was here because the signal voltage was to low causing the engine to intermittently miss. This fault was then cleared using the scan tool, this is done by clicking clear codes on the scan tool.

After this was done the lecturer then put a fault in the system for us to find, the fault that we got was fault code 12, Mass Air Flow sensor, and the condition was no reference voltage to the ECU. Then looking at the live data feed we had to look and see what changed, the main thing was engine load the sensor output was 0 volts as opposed to 1.33 volts. The engine RPM was lower at 874 RPM, those where the two main changes. After doing this then a visual inspection of the engine bay was done, and I found that the MAF sensor connector had been disconnected. So to repair the fault the connector was plugged back in again and the live data feed was checked to make sure that the sensors where working as normal which they where.

http://chinagrabber.com/images/products/detail/Chinagrabber_Car_Scan_Tool_SC69_02.jpg


Next the fault codes had to be cleared this can be done by disconnecting the battery for 30 seconds to let the capacitors discharge or the fault codes can be cleared by using the scan tool to clear them by clicking on clear codes. Now the system is rechecked for codes, by clicking on scan car on the scan tool, no codes where found which meant that the problem had been fixed.

The scan tool can help aid in engine diagnosis by using the live feed to look at all the different sensors of the engine and make sure all of them are working correctly. And by using the scan tool to check codes and having it tell you what sensors or actuators are not working properly. But if the ECU is not logging a faulty sensor a fault, then you can use the live data feed and parameters to make sure that all the sensors and actuators are working as they should.

This is one of the ways you can check EFI(electronic fuel injection) motors for faults.

OXYGEN SENSORS (WS6)

The task to be done was to measure the oxygen sensors output or readings under different engine conditions and loads.

The zirconia type oxygen sensor works by measuring the amount of oxygen atoms passing through the zirconia element. The oxygen sensor produces its own voltage by doing this, it works like this, when the engine runs rich there is low levels of oxygen in the exhaust, this means that there is a high level of migration of oxygen atoms causing a high voltage of up 1 volt. When the engine runs lean there is a high level of oxygen in the exhaust so there is a low migration rate of oxygen atoms through the element which means there is a low voltage down to 0.1 volts. This is basically how a oxygen sensor works.

http://www.boschsparkplugs.net/images/pic_sensor.jpg

The first thing to do was to locate the position of the oxygen sensor, on the Toyota 1zz motor the oxygen sensor is located after the exhaust manifold but before the catalytic converter. There is usually another oxygen sensor located after the catalytic converter (cat) to make sure that cat is working properly and cleaning up the emissions.

The next check was to count how many wires the oxygen sensor has and what each wire does, the oxygen sensor we where testing had 4 wires 2 where white one of which was the heater positive and the other was heater negative or earth. Another wire was black, and that was the signal out wire and the grey wire was the signal earth wire.

The type of oxygen sensor we where working with was the zirconia narrow band oxygen sensor which operates from 0.1 to 0.9 volts.

The first test to do was to back probe the oxygen sensor signal out wire and measure the signal with an oscilloscope whilst the engine is revving at 2500 RPM.

The reading we got can be seen above, this is a good reading as it shows the oxygen sensor cycling between 0.1 and 0.9 volts or rich and lean. A bad reading would be one where there could be sudden drops at regular intervals, this would indicate an engine misfire and trick the ECU into thinking that the engine is running lean and it would make the engine run richer which would increase engine power.

Then we had to count the number of cross counts, or times it goes from low to high in 10 seconds, which was 30 times, this is a good reading as it shows that the oxygen sensor is responding quickly to changes in fuel quantity. If there where less cross counts this could indicate a sluggish 02 sensor and it would not be accurately telling the ECU what the fuel quantity is so the ECU would never be able to run the engine properly as it is never getting whether the engine is running rich or lean at the correct moment so this could cause the engine to run roughly.

The next test was to make the 02 sensor enter closed loop by revving the engine at 2500 rpm then make the engine run lean by suddenly decelerating.

The 02 sensor can be seen running on closed loop then suddenly the voltage drops off as it runs lean, this is a good reading as it shows that the 02 sensor can pick up that the engine is running lean. A bad reading would be one where the voltage may flatten off at 0.3 volts, this would tell the ECU that the engine is not running as lean as it actually is and the ECU would not inject enough fuel as it believes it is running richer than what it actually is and this would make the engine be slightly lacking in power due to the lean mixture.

The number of cross counts on this test was much less at only 7, this is because there are two large levelling off areas, one where the 02 sensor is indicating rich and just after when the 02 sensor is indicating that it is running lean.

The next test was to measure what happens to the signal when the engine runs rich. This is done by making the 02 sensor enter closed loop then blipping throttle to make the engine run rich.

The reading above shows the 02 sensor in closed loop, then the engine was revved up high so that the ECU would inject more fuel to make the engine run rich, this is the reading that we got. The engine runs rich for a very long time then can be seen going lean again, this is because the engine was returned to idle. The reading that we got was a good reading as it showed that the 02 sensor was able to accurately show the engine running rich and for a sustained period of time. A bad reading would be one where the 02 sensor only goes up to 0.6 volts this would tell the ECU that the engine is running leaner than what it actually is and the ECU would inject even more fuel to try and make the engine run rich, this would cause an increase in fuel consumption. This would also mean that the 02 sensor is no longer accurate and the ECU would never be able to make the engine run rich or lean properly as the 02 sensor cannot give the ECU a accurate reading.

The last reading is to measure the response time of the 02 sensor by making it enter closed loop then blipping the throttle to make to it run rich, then measure the time taken between the leanest point and the richest point on the 02 sensor.

The points that we measured from was the leanest point just after the 02 sensor exited closed loop to the riches point, this took around 1.9 seconds to do, this is an average reading and indicated that the 02 sensor is becoming a bit sluggish and is not able to quickly change its signals between rich and lean, a good reading would have been around 1/2 second. All this reading means is that the ECU is getting delayed signals and cannot be as accurate with its air/fuel ratio as it should be. This would mean that the 02 sensor may have to replaced soon.

These are some of the steps that you can take to measure the readings that the oxygen sensor is sending to the ECU and whether it is good or bad readings that the 02 sensor is giving.

On car sensor and actuator testing

OSCILLOSCOPE WAVE PATTERNS (WS3A)

The task to be done was to measure the voltage wave patterns of different engine sensors and actuators using an oscilloscope to determine whether the sensors are in good working condition or not.

MAP SENSOR

The MAP sensors theory on how it works can be found in on my previous post. 

The voltage wave pattern for the MAP sensor, starts off as a low voltage when the engine is at Idle which is a good reading as the MAP sensor produces a high resistance with low air pressure or high vacuum. When the throttle is blipped open the voltage increases correspondantly  to let the ECU know that there is more air going into the engine. The voltage then drops lower than the idle voltage, then stabilizes back to a normal, this is a normal reading, as when the throttle is suddenly snapped shut after the engine has been revved, the engine still is revving. This means that more air is rushing into the cylinders, but there is not enough air to replace the air rushing into the cylinders so a high vacuum is created, which means a higher resistance is created and a lower voltage output is sent to the ECU. The waveform below shows a varying voltage when the voltage reaches around 4.5 volts, this is because of the pulsing air that is caused when the intake valve opens and closes, it causes the air to rush into the cylinders, just a little bit quicker which causes air pressure to change minutely and hence make the waveform vary. 

http://www.aa1car.com/library/map_sensor_waveform.gif

A bad reading of the voltage wave form would be one where the voltage does not go up high enough, this could be caused by a build up of sludge in the intake manifold caused by the Exhaust Gas Recirculation (EGR) system this sludge would then plug up the MAP sensors pressure reader. Which means that the MAP sensor is not reading the correct air pressure in the intake manifold. If the ECU was getting to low of a voltage, this would mean that the ECU would believe that the engine is getting less air than what it actually is and the ECU would not inject enough fuel into the combustion chamber so the engine would be running lean and would be lacking in power.

PRIMARY IGNITION

The primary winding works by grounding the coil or winding, this allows for voltage and current to flow, which in turn builds up a magnetic field. When the coil is ungrounded the magnetic field collapses which means that voltage is then self induced into the secondary winding this voltage then goes to the spark plug or distributor.

The voltage wave form for the primary ignition starts of at 12 volts then sharply drops off to zero volts as the primary coil is ungrounded, this is known as the dwell time. When the coil is ungrounded the voltage spikes to more than 300 volts, this part is known as the firing kilo voltage (KV), this is the effort required to push the spark or voltage to ground through the spark plug. Then there is a stabilising voltage which is around 50 volts, this is known as the burn time or the duration that the spark is grounding, which was in our case around 1.4 milliseconds. Then the voltage returns back to 12 volts to do the cycle again. 

http://www.pc-oscilloscopes.com/images/primary.gif

Faults that can occur with the primary ignition are things like if the spark plug had to large of a gap between the electrode and earth, this would cause for a even higher firing KV as now more voltage is required to push the spark to earth. This would result in a short burn time as most of the voltage has been used up just pushing current through to earth, this would affect engine operation in that fuel would not ignite properly as the fuel has not been exposed to the spark for long enough so that the fuel can fully burn and ignite all of the fuel mixture in the combustion chamber. If the spark plug only had a smaller gap than usual this would mean that there is a lower firing KV as now not so much effort is required to push the spark through to earth, this means that there is a longer burn time as there is still left over energy.

TPS SENSOR

The theory on how the Throttle Position Sensor works can be found on my previous post.

The linear type or potentiometer type TPS wave pattern starts off by sending around a 0.5 voltage reading to the ECU when the TPS is in the idle position. Then as the throttle is opened more the TPS moveable arm uncovers less and less resistor so the voltage increases in relation to the throttle being opened more until the voltage reaches about 5 volts when the throttle fully open. When the throttle is fully open the ECU knows there is a lot of air going into the engine so the ECU injects more fuel to give the engine power. Then the voltage returns back to 0.5 volts when the TPS is back in the Idle position. The ECU needs this sensor to know how much throttle the driver is using so that the ECU can then correct the amount of fuel that is injected into the combustion chamber. The good reading on the oscilloscope wave pattern can be seen on the diagram on the left side of the image below

http://www.aa1car.com/library/tps_waveform.gif

A bad reading for the TPS would be one that is seen on the right side of the image above. This is a flat spot on the potentiometer or an area of high resistance which means that a lot of the voltage is used up trying to push through this resistance. The high resistance  can be caused by dirt build up or just general wear and tear on the potentiometer. This flat spot would trick the ECU into thinking that driver is using less throttle so the ECU will then in turn inject less fuel into the combustion chamber for that brief moment, this would cause a hesitation in the engine during acceleration each time  the throttle reaches this position. However this flat spot is less likely to have any affect during deceleration as most engines do not inject any fuel during deceleration.

FUEL INJECTORS

The next component to be tested using an ocsilloscope is an output or an actuator from the ECU and it is the fuel injector. The fuel injector works by using a transistor to ground the coil in the fuel injector 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 into its seat and the fuel injector is off again and no fuel is being sprayed into the combustion chamber. The fuel becomes atomized when it enters the combustion chamber due to the pressure that it is under.

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 go through the coil and open the injector, when the injector shuts off the voltage increases well above 12volts to over 60 volts. There is a voltage spike  because a magnetic field must be created to lift up the pin that opens the fuel injector that allows fuel passed the injector so that it can be sprayed into the combustion chamber, when the circuit is suddenly shut off the magnetic field collapses the collapsing magnetic field induces current and creates a voltage spike. The wave pattern can be seen in the image below.


http://images.picoauto.com/efi_1-3.png

Faults that can occur with fuel injectors are things like sticking injectors, which mean the wave pattern pattern on the oscilloscope still looks the same but the injector is taking longer to open, if its opening at all. This would cause the engine to run rough as the one of the cylinders is not getting enough fuel and the engine would be running lean, this would be worst affected during acceleration when there is more air going into the engine. 

IGNITION TIMING CONTROL

The Ignition Timing control is a straight on and off signal or digital signal that is sent from the ECU to tell the primary coil to fire, so that a voltage can be sent to the spark plugs, so that a spark can jump to earth which then ignites the air/fuel mixture. The exact theory on how coils work can be seen in my previous post.

The wave pattern that I got for the ignition timing control was an initial 0 volt line which then jumped up to six volts for just over 4 milliseconds then went back to zero volts. This is a good signal as it is strong enough to let the coil know when to fire and the signal is on long enough so that the coil knows when to fire.

There are not many faults that can occur with the ignition timing control, one fault is something like a faulty cam shaft position sensor giving the wrong reference voltage, so the timing control signal is sent at the wrong time causing a misfire in one of cylinders, which would cause the engine to run roughly as now the spark is taking place to soon or to late, or maybe not even at all.

SPEED/RPM/CRANK/CAM SENSORS

On an engine with a distributor the cam and crank sensor is usually located in the distributor, if its on an engine with coil over plugs then the cam shaft position sensor is usually located near the cam shaft on the back or front of the cylinder head. And the crank shaft sensor can be near the crank shaft if its on an engine with coil over plugs.

The cam and crank sensors work by using a fixed magnet, a coil, and a reluctant or spinning bit of iron with teeth on it, for the crank sensor it looks like a gear as it has so many teeth and for the cam it has the same number of teeth for the amount of cylinders the engine has e.g. 4 teeth for 4 cylinders. As the reluctant spins by the fixed magnet and the coil an A/C(alternating current) voltage is induced into the coil as the tooth gets closer the signal gets stronger. This is because the magnetic lines are 90 degrees to each other, as the line comes down and reaches a flattened point this is when the magnetic lines are lining up so no voltage is induced, when the voltage drops below zero and becomes negative this is the change polarity or the lines or magnetism. As the engine rpm's increase the voltage peaks get closer together. And as the engine rpm decreases the voltage peaks from the sensor get further apart. The ECU can determine the speed and the position of the engine by the number of peaks it gets per second this is known as hertz or frequency. The ECU uses this information so that it knows the engine RPM's which is done by the crank sensor and the engine position and what stroke a cylinder is on. The ECU will use these sensors to fire the fuel injectors and the spark plugs at the correct moment.

  

http://www.picoauto.com/waveforms/images/zoom/p4-2.gif

If a fault was to occur with one of these sensors like voltage was not being induced as one of the reluctor teeth passed the coil due to corrosion. Then the ECU would not know what stroke the engine is on or its speed and it wont fire the spark plugs or injectors at the correct time if at all this would cause the engine to run roughly as one of the cylinders is firing at the wrong time or may be not at all. If one of these sensors where to fail completely and not relay any voltage back to the ECU then the engine wont start as the ECU does not know the position of the engine and the speed of the engine so the ECU does not know when to fire the injectors and when to fire the spark plugs. This is why the crank shaft position sensor and the cam shaft position sensor are the two most important sensors in an engine as they are required for the engine to start.

IDLE AIR CONTROL ACTUATOR

The idle air control(IAC) is used to control the amount of air that can by pass the closed butterfly valve or throttle. The ECU controls the amount of air going into the engine by inputs from other sensors around the engine, for example when the engine is cold the ECU will allow more air in the engine during the warm up period to help the engine run smoothly and warms the engine up quicker. The idle air control is also used for when engine load is applied during idle for example the air conditioning compressor is switched on or the electric windows are put down putting a load on the alternator. Or the steering is on full lock and the power steering pump is creating engine load. When one of these things occur the engines revs increase, this is known as idle up, its purpose is to allow the engine to run smoothly and not have the revs drop to low when load is placed on the engine as this could cause it to stall. 

The wave pattern that we got for the IAC was an on and off signal or digital signal varying from 0-12volts, which has two inputs so a two channel oscilloscope was used to measure both inputs, it showed that when one input was off the other input was on and vice versa. This is because two different act on the valve to precisely let a certain amount of air passed the throttle valve, the two inputs do a tug and pull to make exact adjustments to the level of air that is allowed passed. The image below shows when one one input is off the other is on.

http://www.omitec.com/uploads/pics/_2347_20ComptimingBAD.gif

There are four different types of IAC theres the stepper motor type, in which a rod moves in steps back and fourth to allow more or less air into the engine, it works by applying more or less voltage to a coil that moves the rod further forward which is held back by a spring, this type can allow for very precise engine revving control.

http://alflash.com.ua/Temp/79049934_small.gif

The next type is the rotary solenoid type, this works by turning a valve which allows more or less air passed the throttle valve and is used to control all idle up situations like engine load and cold start. This is controlled by using two coils to act on the valve to open it more or less.

The next IAC is the duty control ACV type. This type is incapable of allowing large amounts of air passed the closed throttle so a mechanical air valve is used for cold start situations. This type of  IAC works by applying a duty cycle voltage to a solenoid at different Hz, the higher the Hz the more the valve opens and the more air is allowed passed the throttle valve.

The last type of IAC is the on/off vsv IAC, this type of  IAC cannot pass large amounts of air, so a mechanical air valve is used during cold starts. This type of  IAC is vacuum controlled or vacuum switching valve(vsv). When the coil or solenoid is powered by the ECU then the valve is either on or off according to the correct conditions, it cannot control exactly how much air has gone passed its either on or off.

Faults that can occur with the IAC is that the throttle valve gets clogged up with sludge, which means some of the IAC is used to keep correct engine idle. And the worse the engine valve gets the more the IAC ability is used up to correct engine idle. This means that there is less ability for idle up under engine load and the engine rpm may not increase enough for the load and the engine could run roughly or stall as the IAC cannot increase the revvs enough as it is already being used up.

EXHAUST GAS ANALYSIS (WS7)

The task that had to be done was to use an exhaust gas analyser to check the emissions of a 2003 Ford Ka, 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 4.46% 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 1839 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 9.26% O2 in the emissions.

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 1.114% which is low so it is not anything to worry about it shows the engine is burning fuel efficiently. 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 and all of the fuel is being burnt. O2 levels are lower as more fuel is being burnt which means there is more oxygen being burnt the O2 levels where at 1.64% which means all these readings are good and shows the engine is combusting fuel efficiently.

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 decreased CO levels as they are 0.179% but HC level is high as it was at 959ppm, 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 9.65% 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 which means a lot of oxygen comes into the combustion but since combustion is not burning all of it a lot of 02 comes out the exhaust pipe.

The next test was to create a rich air/fuel mixture by spraying ethanol or starter fluid into the intake to create the rich condition. There is a rich air/fuel ratio because more fuel or hydro carbons is going into the engine so  there is more fuel to burn . This means that there is an extremely high level of HC at 2313ppm this is because of the rich air/fuel mixture and there is to much gas to burn so a lot of it is unburnt hence the high level, this also means there is higher CO at 3.947% as CO is created by a rich air/fuel mixture and there not being enough oxygen to create O2. CO2 is a bit lower at 12.59% as the engine is not running efficiently anymore this means that there is low level of O2 at 0.58% 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 primary and secondary coils or windings. 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 at 0.58% as there was still unburnt fuel going into the exhaust which meant that the oxygen was not burnt this resulted in a high reading for C02 of 13.6% . HC was extremely high due to the fact that one cylinder was not burning any gas this meant that HC was at 1240ppm, oxygen levels where high at 7.61% as well because of the fact that no oxygen was burnt because combustion was not taking place so the oxygen could not be burnt.

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 0.247% because there was no unburnt fuel from a rich air/fuel mixture this meant that the HC was low at 217ppm because there is no unburnt fuel however CO2 levels where lower at 11.68% 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 5.17% 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 last test was to make optional changes to see what happens to the emissions so the air conditioning was switched on to see what would happen. CO is at 0.3% this is because the a/c has bought the engine off idle and combustion is taking place more efficiently now so there is not much left over O2, and the O2 level was at  0.55%. HC was incredibly low at 8ppm, showing that combustion is burning almost everything, CO2 was at 14.73% showing that combustion was basically taking place perfectly because the revvs have been increased due to a some engine load from the a/c.

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:

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PETROL 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 12.85volts 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 12.70 volts, number two injector was getting 12.71volts, number 3 injector was getting 12.74 volts, and the last injector was getting 12.79 volts.


 The above results shows 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.


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The first test was to make sure that the injectors where grounding properly using a logic probe, if the injector was grounding then the lights on the logic probe would flash each time the injector grounded showing a complete circuit. All four of the injectors grounded which is a good result and shows that each of the injectors is grounding as it should. The reason that the reason that the injectors are tested that they are grounding is because the ECU grounds the injectors, so it is made sure that the ECU is actually grounding the injectors before any more tests are done.

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 4.8% of the time, injector 2 was open 4.7% of the time, injector 3 was open 4.7% of the time and injector 4 was open 4.7% 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 as the engine is now missing cylinder.

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  injector 1 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 45Hz, injector 2 was 50Hz, injector 3 was 54Hz and the last injector was 52Hz. 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.

Other faults that can occur with fuel injectors are sticking injectors, that can be caused by a build up of grime or carbon in the injector which means that the pin wont lift or will only lift slightly meaning that one of the cylinders will be running lean. This would cause the engine to run roughly as the cylinders is running lean or maybe not getting any fuel. And if that fuel injector was tested the results would show that its running normally, the only way to see that there is a problem is to wire the injector up to an oscilloscope that measures current and not voltage, and it will show that the injector is not opening as a normal injector opening will have a bit of a levelling off area just as the pin on the injector opens but if it doesn't open then the current line just increases the whole time. This is one of the ways to tell whether its not opening, the other way is to listen for the clicking as the pin opens and shuts.

These are some of the checks that you can do, to see whether the petrol fuel 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.