Scan Tool Diagnosis

for this exercise i let the engine run at idle

the engine was a 1ZZ-FE

i plugged the diagnosis plug into the engine diagnosis port, answered all the questions about the engine details and then recorded my data

below is a table of live data from the engine

Type of information	Letters to describe	Value of data	units
how much air comes in	MAF	2.55	Gm/s
Engine RPM	engine speed	700	RPM
Throttle angle	TPS	11	%
Engine coolant temperature	ECT	73	C°
intake air temperature	IAT	22	C°
Fuel injection opening pulse	injector pulse time	2.7	ms
transmission select position	shift	4
vehicle speed	0	0	km/h
oxygen sensor	O2	0.79	V
fuel trim	short term fuel trim	-20.3	%
idle control	IAC	37.5	%
power steering condition	pwr steering	NA
air conditioning condition	air con	NA
malfunction indicator light	engine warning light	on	on

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my lecturer then put a fault in the engine and i looked the codes up in the scan tool.

code number - P0120
System affected - TPS
Condition described - circuit malfunction

i then checked the parameter identification

the value of data was 0%

i then did a visual inspection of the sensor to see if there was anything visually wrong with it

i did this by checking the wires and making sure the voltages were correct readings

after checking the ground wire and output to ecu, i found that the reference voltage was out of spec. i checked this by checking the voltage coming out of the ecu for the 5v reference and found out that it was not reading 5 volts

i then cleared the codes using the scan tool, i then turned the key off and then back on and found that the codes had been cleared.

a scan tool is useful because it tells you where to look for the problem on the engine, however you still need to know how to fault find on the component.

Exhaust Gas Analysis

to record the following data i placed the exhaust analyser into the exhaust pipe of the vehicle.

Carbon Monoxide (CO) - if the engine is putting out these gasses, the catalytic converter is not working correctly. with a high number, the catalytic converter is not working properly.

Hydro Carbons (HC) - with his gas, we can tell about the misfires in the engine.

Carbon Dioxide (CO2) - this gas will show us if the catalytic converter is working correctly. with a high number, this will tell us that the catalytic converter is working correctly.

Oxygen (O2) - these levels will show us if the engine is running too ritch or too lean. if the oxygen levels are high, the engine is running lean. if the oxygen levels are low the engine is running too ritch.

i then went ahead and let the analyzer run its course and test the emissions when the engine was idling cold and recorded the four gasses

CO - 41% - this shows us that the cat is not working because these gasses are quite high.
HC - 340ppm - this shows us that the engine is misfiring a lot
CO2 - 12% - these levels are quite low, this shows us that the cat is not working correctly.
O2 - 0.6% - this shows us that the engine is running that the engine is running ritch.

i then let the engine warm up to operating temperature and recorded the four gasses again.

CO - 3% - this shows me that the cat is still not working correctly because this number should almost be 0
HC - 171ppm - this shows me that there is not as many misfires in the engine because the number has dropped.
CO2 - 12.8% - this is quite low which still indicates that the cat is not working correctly
O2 - 0.08% - this shows me the engine is running even more ritch than at idle.

after the previous test i let rev'd the engine up to 2500 rpm and recorded the four gasses

CO - 39% - this tells us the cat is still not working and needs replacing because this gas should not be getting released.
HC - 245 ppm - this shows that as the engine is rev'd up, is gets an increase in misfires
CO2 - 12.8% - this is still low which indicates the cat is broken.
O2 - 0.18% - this number has gone up quite a bit which tells us the engine is running a little bit lean.

with the results of these tests, it is clear that the catalytic converter is broken and not filtering the gasses, it also tells us that the engine has misfire.
the carbon monoxide was too high and is very harmful to breathe in.

Oscilloscope Patterns to Capture

Engine Coolant Temperature Sensor

i hooked the engine up to an oscilloscope and then let it idle while is was cold and kept reading the oscilloscope while it was heating up

in the above oscilloscope reading, you can see as the line is at the higher point it is cold and when the engine starts warming up the line starts going down, this means the voltage is dropping.

this reading could be faulty if the sensor had a bad earth or a faulty thermistor this could cause the engine to over heat.



MAP Sensor

For this sensor i hooked up the oscilloscope up to the output wire and to the ground wire i then gave then engine a few quick revs

when i snapped the accelerator i found that the voltage went up because there was no vacuum and when i had the engine at idle there was not much voltage because there was full vacuum.

is the sensor was giving a faulty reading it could be because there is a bad earth or the vacuum line is not on properly or leaking.

if the hose was leaking or not attached the sensor would be reading no vacuum so it would tell the ecu to squirt maximum fuel into the combustion chamber.



Throttle Position Sensor

with this TPS i did not turn the engine on but switched the ignition on, i hooked the oscilloscope to the output wire and the ground wire.

i then paused an image of the oscilloscope reading once i had done a half throttle position and a wide open throttle position.

below is the picture of the oscilloscope reading that i have drawn.

at point A, this is when the engine is at idle. point B is when i put the throttle half open, point D is when i put wide open throttle.

if the TPS was giving a wrong reading it could be because the sensor was not grounded properly or a terminal is loose. the sensor could also be faulty.

this would send the wrong voltage to the ecu which would tell the injectors to stay open too long or too short, this would not let engine run correctly for drivers needs.



Intake Air Temperature

this sensor works the same way as the coolant temperature sensor. the higher the temperature, the lower the voltage.

i hooked up this sensor to the oscilloscope on the output wire and the ground wire.

to make the temperature go up on the intake, i got a heat gun and slightly raised the temperature so i could get a visible reading.

as i put the gun into the intake, the voltage begins to drop.

if the sensor was giving an incorrect reading, it could be because the sensor is not grounded properly or has a faulty thermistor in it.



RPM Cam


for this test i let the engine idle and hooked up the oscilloscope to the output wire and a good ground.

below is a recording of what the oscilloscope reading looked like

as you can see, cylinder 1 is not recognized as the other 3 cylinders, this is because the ecu needs to recognize how fast the cam is spinning because this is what the engine timing gets its readings from.

if the sensor was giving faulty reading the engine would run advanced or retarded depending on what voltage is being sent to the ecu. this could mean a bad earth or faulty sensor that needs replacing.



RPM Crank

this sensor was recorded at idle and had the oscilloscope hooked up to the output wire and a good ground

below is a drawn reading of the oscilloscope reading

as the waveform is at its peak, the cog gear is closest to the pick up sensor when the wave form is at its lowest point, the cog tooth is furthest away from the sensor. this tells the engine how many RPM's it is doing by sending the signal to the ecu.



Oxygen Sensor

i hooked this sensor up to the oscilloscope on the output signal and good ground.

i then let the engine idle and watched the waveform change by a small difference.

below is a drawn picture of what the waveform looked like on the oscilloscope

as the waveform goes slightly up, this means the engine ran slightly ritch and the O2 sensor voltage went up which told the ecu to make it run a bit leaner, its then increased which the sensor told the ecu again and it ran even more lean which evened out the idle when it oscillates back to normal voltage.

Fuel Pressure and Flow

the fuel pressure and flow are one of the most important parts of the injection system, this depends on how much fuel gets squirted into the injectors.

before i started this test, i checked the specifications of the fuel pressure for this engine (4A-FE). the pressure was 38 to 44 PSI. I then did a visual check to make sure there was no leaks in the system.

i then measured the fuel pressure of the engine with the ignition on but the engine off, there was no pressure because the engine had not been on.
then i turned the engine on and let it idle for a few minutes and found the pressure raised to 36 PSI.
after that i clamped the fuel return line to find that the pressure went off the scale to above 87 PSI.

the next test i did, i took off the vacuum line and blocked it so the engine thought it was at wide open throttle, this brought the pressure to around 45 PSI.
i then turned the engine off but left the key on and watched the pressure drop to 37 PSI, this is the residual pressure.


if the engine had low fuel pressure the vehicle would have a rough idle and be running lean, this would happen because the injectors would not have enough pressure to squirt the right amount of fuel into the combustion chamber. this could mean that the pressure regulator not letting fuel rail build enough pressure and could be stuck open or a faulty fuel pump.

If the engine had a high fuel pressure, this would mean the vehicle would have a boggy idle because the engine would not be burning the fuel properly, this would be creating carbon monoxide. the injectors would be squirting too much fuel into the combustion because the pressure would be too high, this could also cause the injectors to dribble. this could mean the pressure regulator is stuck closed and not allowing pressure out into the return line.

Primary & Secondary Ignition patterns

Primary Voltage Patterns

in this exercise i set up an oscilloscope to look at the primary ignition pattern of my engine while it was idling and warmed up (closed loop)
i rigged this oscilloscope up by putting the positive feed from the scope onto a pin which was inserted on the input down the connector of the distributor, i then put the negative/ground wire on a good common earth.

below is a table of the recordings i collected from the ignition patterns:

Cyl 1	Cyl 2	Cyl 3	Cyl 4	Primary Ignition
248v	248v	248v	248v	Firing Voltage
55.6v	55.6v	55.6v	55.6v	Burn Voltage
1.48ms	1.48ms	1.48ms	1.48ms	Burn Time
6.2ms	6.2ms	6.2ms	6.4ms	Dwell Time

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volts per division = 50v              milli seconds per division = 2ms


if we follow the line across the screen (left to right), when the line drop, this is called the DWELL TIME, this is when the circuited is grounded.
when the line is at its peek and goes all the way up, this is called the FIRING VOLTAGE, this is the voltage that it takes to push through the high tension leads and to spark plug.
when the line drops down and slightly scribbles across, this is the BURN TIME, this is the time we use to keep sparking the so we can burn all fuels in the combustion chamber.
when the line goes back down but oscillates, this is because the magnetic field is taking time to release.

The raster and stacked display you can put the patterns on top of each other, this helps to to compare times better and makes it more clear to see the length of things.


Secondary Voltage Patterns

in this exercise i had to set up an oscilloscope to the secondary ignition. i did this by attaching a belt around the distributor, this would sense the voltages through the distributor cap, i also rigged up a common earth.

i then let the engine idle at operating temperature and recorded my reading and put them into a graph.

Cyl 1	Cyl 2	Cyl 3	Cyl 4	Secondary Ignition
5.4kv	8.2kv	5.9kv	6.2kv	Firing Voltage (killer volts)
0.75ms	0.87ms	0.65ms	0.71ms	Burn Time (milli seconds)
9.8kv	8.4ms	9.8ms	9.0ms	Snap acceleration

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this waveform is the same as the primary waveform, the only difference is that the secondary pattern does not have a dwell time..
 the results from this test are all good and within specifications of the engine type (4A-FE)
when i snapped the accelerator i expected the burn time to be longer because it had more fuel inside the combustion chamber to burn, therefor the burn time needed to increase so it could burn all of the gasses .



Shorted Secondary

Cyl 1	Cyl 2	Cyl 3	Cyl 4	Secondary ignition
5.4kv	3.2kv	5.9kv	6.2kv	Firing Voltage (killer volts)
0.75ms	____	0.65ms	0.71ms	Burn Time (milli seconds)

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in the above table i have shorted number 2 cylinder to ground and it has a lower firing voltage because it has less resistance to make it fire.

Below is the waveform drawn from the oscilloscope:

the peek firing voltage says 10 volts but it is really 3.2kv

there is only a firing voltage on the graph because there is not any burn time to read on the oscilloscope because the plus is not in the cylinder.



Spark Tester

the spark plug tester is like a spark plug that goes on the end of a HT lead, this lets us know if the spark plug in engine is faulty or the plug gap is too large or too small

if the gap was too big, the burn voltage would be a lot higher and if the gap was too small the burn voltage would be a lot smaller. this happens because it takes more voltage to push the electricity across the spark plug gap if it is bigger. if it is smaller it takes less voltage.

Flash Codes

Flash/Blink codes
If the check engine light was on when the ignition is on, there is a fault in the system some where.
for this test i read the workshop manual and found out that i needed a jumper wire to find out theses faults. i had to connect the jumper wire to two terminals in the fuse box and join them together (TE1 and E1).
When i connected the jumper wire to the two terminals, the check engine light would then start flashing and make a pattern that i had to look up in the manual to find out what they mean.

For example: if the light flashed 2 times and then 4 times. i would look up the number 24 in the manual.

Trouble codes or Fault codes
below is a table of recordings that came up as faults on my engine when the tutor made some faults for me to find.

Code Number	System Affected	Condition Described
24	air intake temp	incorrect air fuel ratio
31	vacuum sensor	too much fuel being squirted in
41	TPS	bad idle RPM

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Visual Inspection to find fault and repairing fault
-air intake temp sensor was unplugged when i had a look at it, to repair this i plugged it back in
-vacuum sensor was unplugged when i checked it, i then plugged it back in.
-TPS sensor was also unplugged, to repair this i had to plug it back in.


Clear Codes and Recheck for them
i turnedd the ignition off after i had fixed the faults, this also  clears the codes.
when i turned the ignition back on the check engine light was off and there were no faults in the system.

How could the faults affect engine performance?
these faults would have made the engine not idle correctly and eventually blow up because of the pinging, this was due to the vacuum sensor being unplugged which made the ecu think that it was at wide open throttle so it was putting maximum fuel in.

After the engine light is off i should do another visual check to make sure everything is plugged in properly and the engine is running correctly.

Practice Back-Probing

review of multimeter
First of all, i turned on my meter and set it to ohms. i then made sure that the probes were not touching each other and i got a reading (OL) this reading means that there is an open circuit.

reading ohms with wires connected
i set my multimeter to ohms and touched the two probes together. the reading i got was 0.4 ohms, this is the resistance in the circuit. this is quite a high recording from a multimeter, it should generally be around 0.2 or less.

practice back probing connectors
for this test i used a hard shell connector and gently probed a pin into the connector so it fits beside the wire and then i put my multimeter prong onto the pin, i then put my other multimeter prong through the other side of the connector and recorded the resistance. the reading i got was 0.5 ohms.
this was a good connection because it was a solid reading and the numbers weren't jumping up and down, also if i had a bad connection the resistance would be higher.