I wonder whether anyone out there can shed some light on a problem I am having, I have owned citroens for the last 25 years so both pleased to find this site and hopeful someone may be able to help.
I have a 92 XM V6 Sei Estate, Manual Gearbox, its been fine for the last few years just the usual stuff. But about 6 months ago I noticed a small misfire under load, it only does it when warm and under light engine load, if I floor it the fault is not there, if I drive everywhere at 90 its not there!
Over a period of time I have systematically replace everything I can think of, I have also had the ECU decoded and its not recording any faults. Here's a list of the parts changed.
Ignition System.
Plugs, HT Leads, Coil, Ign Module, Dist cap Roto Arm.
Fuel System
Fuel Pump, pressure reg, fuel damper, throttle potentiometer, idle bypass valve, map sensor.
I have also changed the Air Filter, tried injection cleaner, and changed the ECU. Also drained the tank, Fuel pressure is a 2.7 - 3 bar.
To be clear I have used second hand parts mostly, but none of the above changed the symptoms of the fault one little bit, still drives faultless from cold for about 10 miles then starts to loose what feels like a couple of cylinders, no problem on the motorway but a real pain in traffic. It idles fine, temp remains constant, CO and HC are fine.
HELP!!!!
Any ideas would be appreciated,
Cheers
Joe
XM V6 Misfire
Moderator: RichardW
Firstly have you done all the work yourself? the reason I ask is i understand that the plugs on the rear cylinders are hard to get at and its not unknown for 'professionals' to leave them.
My first call would be to check and meter the resistance of all the HT leads. They should all be about equal and 10K ohms in resistance. Digital multimeters are available from Maplins for £2.99 - less than the cost of 1 new HT lead.
Its also worth having a good look under the bonnet in the dark to see if there are any stray sparks from the HT system when the engine is running.
jeremy
My first call would be to check and meter the resistance of all the HT leads. They should all be about equal and 10K ohms in resistance. Digital multimeters are available from Maplins for £2.99 - less than the cost of 1 new HT lead.
Its also worth having a good look under the bonnet in the dark to see if there are any stray sparks from the HT system when the engine is running.
jeremy
Hi,
Yep, I did all the work, did the plugs on the back, also removed the top cover and now use plug separaters to keep leads apart as well as a thorough inspection in pitch black darkeness. Cant see any arcing.
I cant normally make the fault happen when stationary.
I will give the leads a measure but when I scoped them the patterns where all the same length.
It is typical of a leads/coil fault.
I used to work on Citroen's in the 80's and have always kept the faith, maybe I am loosing it these days!
Yep, I did all the work, did the plugs on the back, also removed the top cover and now use plug separaters to keep leads apart as well as a thorough inspection in pitch black darkeness. Cant see any arcing.
I cant normally make the fault happen when stationary.
I will give the leads a measure but when I scoped them the patterns where all the same length.
It is typical of a leads/coil fault.
I used to work on Citroen's in the 80's and have always kept the faith, maybe I am loosing it these days!
I would try either the MAP (or MAF) sensor and the lambda probe, i believe both of these are out of the loop for the first few minutes until the engine has warmed up, and they seem to show themselves up as a pinking at low revs going up hills with your foot flat on the floor, and a misfiring sounding idle with slight popping from the exhaust
have you checked the LT connections to the coil? If still using the original Cit connector that can give problems, been reported on xm-l on 2.0tct in spain as a problem, maybe yours too?
regards
Dave
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Joe T</i>
Hi,
Yep, I did all the work, did the plugs on the back, also removed the top cover and now use plug separaters to keep leads apart as well as a thorough inspection in pitch black darkeness. Cant see any arcing.
I cant normally make the fault happen when stationary.
I will give the leads a measure but when I scoped them the patterns where all the same length.
It is typical of a leads/coil fault.
I used to work on Citroen's in the 80's and have always kept the faith, maybe I am loosing it these days!
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
regards
Dave
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Joe T</i>
Hi,
Yep, I did all the work, did the plugs on the back, also removed the top cover and now use plug separaters to keep leads apart as well as a thorough inspection in pitch black darkeness. Cant see any arcing.
I cant normally make the fault happen when stationary.
I will give the leads a measure but when I scoped them the patterns where all the same length.
It is typical of a leads/coil fault.
I used to work on Citroen's in the 80's and have always kept the faith, maybe I am loosing it these days!
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Thanks for this guys its giving me hope,
Right, changed the Map Sensor, also checked the pipe for leaks, I have not changed the Lambda Probe, the CO and HC are fine and also no codes have cropped up in the ECU, could it still be faulty?
It takes at least 5 to 10 mins for the fault to start. Engine temp has to go over 90 the stat has to open I reckon before it starts, on a cold morning when it hasnt been used for a few days I get further. The fault is so regular there is a bridge on my way to work thats the point it starts.
LT Ign Module plug replced also had it apart and check the repaired connectors, I have given the engine loom wiring a good tug about on idle and it dont miss a beat.
I have sprayed round the inlet manifold for leaks with a WD etc
None of the plugs are oiling up, they all appear the same colour.
There is a sensor on the throttle body does that do anything special?
I would have gave up ages ago but I honestly dont know what to replace this with, I had a CX25 DTR Turbo before this and that was a wrench when we finally parted company.
Right, changed the Map Sensor, also checked the pipe for leaks, I have not changed the Lambda Probe, the CO and HC are fine and also no codes have cropped up in the ECU, could it still be faulty?
It takes at least 5 to 10 mins for the fault to start. Engine temp has to go over 90 the stat has to open I reckon before it starts, on a cold morning when it hasnt been used for a few days I get further. The fault is so regular there is a bridge on my way to work thats the point it starts.
LT Ign Module plug replced also had it apart and check the repaired connectors, I have given the engine loom wiring a good tug about on idle and it dont miss a beat.
I have sprayed round the inlet manifold for leaks with a WD etc
None of the plugs are oiling up, they all appear the same colour.
There is a sensor on the throttle body does that do anything special?
I would have gave up ages ago but I honestly dont know what to replace this with, I had a CX25 DTR Turbo before this and that was a wrench when we finally parted company.
I think their are 2 temp probes a green plug and a blue plug, well I tried driving it with them disconnected, it ran rough but I could still feel the same fault through it.
Its almost like a rev limiter cutting in, it does feel electrical, but who knows.
What about injectors?
Trouble is getting hold of bits at sensible money for one of these is a nighmare, its taken months to accumulate the little lot I have gone through, mind you building up a nice spares collection!
I was hoping I might not be alone in XM V6 ownership and perhaps someone has a had a similar fault.
Thanks Anyway Guys
Its almost like a rev limiter cutting in, it does feel electrical, but who knows.
What about injectors?
Trouble is getting hold of bits at sensible money for one of these is a nighmare, its taken months to accumulate the little lot I have gone through, mind you building up a nice spares collection!
I was hoping I might not be alone in XM V6 ownership and perhaps someone has a had a similar fault.
Thanks Anyway Guys
Hello Joe T.
Did you checked also the lambda sensor ?
The voltage quickly moves between 0,1 and 0,8 volts(warm engine).
If it has 4 wires the two same color are for the build in heater, the others are ground and signal
It can also give wrong signal by false air when the exhaust isn t close enough, so the ECU thinks the mixture is poor and enriches it.
Greetings.
Willy M.
Did you checked also the lambda sensor ?
The voltage quickly moves between 0,1 and 0,8 volts(warm engine).
If it has 4 wires the two same color are for the build in heater, the others are ground and signal
It can also give wrong signal by false air when the exhaust isn t close enough, so the ECU thinks the mixture is poor and enriches it.
Greetings.
Willy M.
look at this link
http://www.kfz-tech.de/Engl/LSondenSpann1.htm
http://www.kfz-tech.de/Engl/LSondenSpann1.htm
another picked from the web
OXYGEN SENSOR: INSPECTION AND TESTING By Mark Calabrese
In last month's column I wrote a little about the theory and operation of your engine's Lambda sensor This month I will address the inspection and testing of this critical component.
As I stated in part one of this article, the O2 sensor usually performs unnoticed for at least 50,000 to 60,000 miles. If you suspect your sensor has failed, or is not operating up to specifications, there are several inspections and tests that can be performed before laying out the money for a new sensor.
The first point of inspection should be the connector for the sensor. Because an O2 sensor's output is a very small voltage (1 volt or less), any problem at its connection can cause the output to be erroneous. Make sure this connection is free from corrosion, grease. or any other foreign substance. Also check that the sensor's wires are not damaged, especially from heat from the exhaust manifold.
Next jack the car and place stands under it to support the car's weight. NEVER WORK UNDER A CAR WITHOUT JACK STANDS. The O2 sensor, which looks like an overweight spark plug can be found between the exhaust manifold and the catalytic converter Once again carry out an inspection, this time of the area surrounding the sensor An oxygen sensor must have a free flow of ambient air to com pare with the exhaust gas in order to function properly. If a sensor is blocked by mud or other trash and can not `breathe" it will not function.
With the inspections completed, test the output of the sensor with your Digital Multi-Meter. Don't make the mistake of using an older generation analog meter to test the sensor, as possible damage to the electronics of the DME computer and the O2 sensor can result.
Depending on the age of your Bimmer and the Motronic system installed, there will either be a one, three, or four wire O2 sensor. With only one wire, there's no problem determining which wire is the signal wire. If it is a three or four wire system and you don't have an Electronic Trouble Shooting manual to look up the details of the wires, there is a simple method to determine which wire is the signal wire. Place your DMM in the DC volt position and attach the black common test lead to a good chassis ground. Then find the O2 sensor's connector and disconnect it from the car's computer With the engine running, use the red test lead (positive) to probe the wires of the O2 sensor. Only one wire should have an output and it should be under one volt.
Once you find the correct wire, stop the engine and reconnect the sensor You will then need to break out the signal from the sensor with it still connected to the computer. I have spliced in a short test wire which enables me to test the sensor at any time. You could also use a test lead end that has a small alligator clip with a piercing tooth that can pene- trate the wire's insulation. I prefer the first method as it allows me to install a long test set of wires which I can then hook up to my meter and place in the front seat of my car. This setup allows me to test the sensor under real world circumstances as I drive.
With the sensor hooked up to the meter, restart the engine and let it warm up to norma) operating temperature. Set the meter to DC volts and then set it to use the four volt range. If your meter has the ability to record minimum, maximum, and average voltage readings. use this feature as it allows you to record and save the O2 sensor's signal the whole time it's under test. With the engine at temperature, run the throttle up to 2000 RPM and hold it for 30 seconds and then release it. Goose the throttle once and then press the meters hold button. This locks in all the voltage readings captured during the test. If your sensor is working properly, the minium voltage should be under 0.200 DC volts, the maximum at least 0.700 DC volts and the average close to 0.450 DC volts. A rich running engine would show a much higher average. Use the chart as a simple guide for diagnosing oxygen sensors.
OXYGEN SENSOR TEST RESULTS
Min Max Average TestResults ------- ------- ------- ----------------------------------
<200 >700 400-500 Oxygen Sensor is OK
>200 NA 400-500 Replace Sensor
NA <700 400-500 Replace Sensor
<200 >700 <400 Running lean
<200 <700 <400 System is lean. Enrichen mixture to see if the sensor reacts, if not, replace sensor.
<200 >700 >500 Running rich
>200 >700 >500 System is rich. Lean mixture to see if the sensor reacts, if not, replace sensor.
all numbers in millivolts (mV).
Another important test to consider is how fast a sensor reacts to a mixture change. Check this by forcing the engine lean (remove the oil filler cap during engine operation), and then rich (inject propane into the air inlet, or restrict the flow of intake air). A properly functioning sensor should change voltages instantly. Faulty sensors generally lock onto one voltage and do not cycle up and down. Shorted sensors will read 0 volts.
Of course, it goes without saying, you should never condemn the O2 sensor unless you're sure the rest of the engine is running properly. There are many engine problems could point out a leaky fuel injector would cause a higher then average O2 sensor reading, a torn intake hose would cause a lean mixture, etc.
One final caution, some people are under the impression that disconnecting the O2 sensor will benefit them and give them more power This is not the case. The sensor is a very important component in the engine management system and is there to fine tune the fuel injection system and give you an optimum running engine
OXYGEN SENSOR: INSPECTION AND TESTING By Mark Calabrese
In last month's column I wrote a little about the theory and operation of your engine's Lambda sensor This month I will address the inspection and testing of this critical component.
As I stated in part one of this article, the O2 sensor usually performs unnoticed for at least 50,000 to 60,000 miles. If you suspect your sensor has failed, or is not operating up to specifications, there are several inspections and tests that can be performed before laying out the money for a new sensor.
The first point of inspection should be the connector for the sensor. Because an O2 sensor's output is a very small voltage (1 volt or less), any problem at its connection can cause the output to be erroneous. Make sure this connection is free from corrosion, grease. or any other foreign substance. Also check that the sensor's wires are not damaged, especially from heat from the exhaust manifold.
Next jack the car and place stands under it to support the car's weight. NEVER WORK UNDER A CAR WITHOUT JACK STANDS. The O2 sensor, which looks like an overweight spark plug can be found between the exhaust manifold and the catalytic converter Once again carry out an inspection, this time of the area surrounding the sensor An oxygen sensor must have a free flow of ambient air to com pare with the exhaust gas in order to function properly. If a sensor is blocked by mud or other trash and can not `breathe" it will not function.
With the inspections completed, test the output of the sensor with your Digital Multi-Meter. Don't make the mistake of using an older generation analog meter to test the sensor, as possible damage to the electronics of the DME computer and the O2 sensor can result.
Depending on the age of your Bimmer and the Motronic system installed, there will either be a one, three, or four wire O2 sensor. With only one wire, there's no problem determining which wire is the signal wire. If it is a three or four wire system and you don't have an Electronic Trouble Shooting manual to look up the details of the wires, there is a simple method to determine which wire is the signal wire. Place your DMM in the DC volt position and attach the black common test lead to a good chassis ground. Then find the O2 sensor's connector and disconnect it from the car's computer With the engine running, use the red test lead (positive) to probe the wires of the O2 sensor. Only one wire should have an output and it should be under one volt.
Once you find the correct wire, stop the engine and reconnect the sensor You will then need to break out the signal from the sensor with it still connected to the computer. I have spliced in a short test wire which enables me to test the sensor at any time. You could also use a test lead end that has a small alligator clip with a piercing tooth that can pene- trate the wire's insulation. I prefer the first method as it allows me to install a long test set of wires which I can then hook up to my meter and place in the front seat of my car. This setup allows me to test the sensor under real world circumstances as I drive.
With the sensor hooked up to the meter, restart the engine and let it warm up to norma) operating temperature. Set the meter to DC volts and then set it to use the four volt range. If your meter has the ability to record minimum, maximum, and average voltage readings. use this feature as it allows you to record and save the O2 sensor's signal the whole time it's under test. With the engine at temperature, run the throttle up to 2000 RPM and hold it for 30 seconds and then release it. Goose the throttle once and then press the meters hold button. This locks in all the voltage readings captured during the test. If your sensor is working properly, the minium voltage should be under 0.200 DC volts, the maximum at least 0.700 DC volts and the average close to 0.450 DC volts. A rich running engine would show a much higher average. Use the chart as a simple guide for diagnosing oxygen sensors.
OXYGEN SENSOR TEST RESULTS
Min Max Average TestResults ------- ------- ------- ----------------------------------
<200 >700 400-500 Oxygen Sensor is OK
>200 NA 400-500 Replace Sensor
NA <700 400-500 Replace Sensor
<200 >700 <400 Running lean
<200 <700 <400 System is lean. Enrichen mixture to see if the sensor reacts, if not, replace sensor.
<200 >700 >500 Running rich
>200 >700 >500 System is rich. Lean mixture to see if the sensor reacts, if not, replace sensor.
all numbers in millivolts (mV).
Another important test to consider is how fast a sensor reacts to a mixture change. Check this by forcing the engine lean (remove the oil filler cap during engine operation), and then rich (inject propane into the air inlet, or restrict the flow of intake air). A properly functioning sensor should change voltages instantly. Faulty sensors generally lock onto one voltage and do not cycle up and down. Shorted sensors will read 0 volts.
Of course, it goes without saying, you should never condemn the O2 sensor unless you're sure the rest of the engine is running properly. There are many engine problems could point out a leaky fuel injector would cause a higher then average O2 sensor reading, a torn intake hose would cause a lean mixture, etc.
One final caution, some people are under the impression that disconnecting the O2 sensor will benefit them and give them more power This is not the case. The sensor is a very important component in the engine management system and is there to fine tune the fuel injection system and give you an optimum running engine
-
Stempy
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Not missing the AX - Contact:
<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by Joe T</i>
Hi
So I check between Signal and Earth or do I use a chassis earth?
Is it ok to do this while the engine is running?
Cheers
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
You can try to check it but either by measuring the voltage or by measuring its resistance but you may not pick up a fault just by these means. You'd be better off just replacing it. If it's like most sensors it will have a low resistance when hot and a high resistance when cold, ranging from about 300 ohms to about 4k ohms.
Hi
So I check between Signal and Earth or do I use a chassis earth?
Is it ok to do this while the engine is running?
Cheers
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
You can try to check it but either by measuring the voltage or by measuring its resistance but you may not pick up a fault just by these means. You'd be better off just replacing it. If it's like most sensors it will have a low resistance when hot and a high resistance when cold, ranging from about 300 ohms to about 4k ohms.