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Apparently, that is how the ECM monitors for misfire:- tiny variations in the crank angular velocity.
Must admit I was a bit incredulous when I read it.
Here's what the SERVICE TRAINING COURSE 881 V6 / V8 ENGINE MANAGEMENT has to say (apologies for shouting):
"Misfire Detection / CAN Data
The ECM is able to detect misfire by monitoring crankshaft acceleration (CKPS signal). In order to reduce the possibility
of false misfire diagnosis, the ECM uses the ABS/TCCM CAN data – left and right rear wheel speeds – to
determine if the vehicle is operating on a rough road."
Apparently, that is how the ECM monitors for misfire:- tiny variations in the crank angular velocity.
Must admit I was a bit incredulous when I read it.
Here's what the SERVICE TRAINING COURSE 881 V6 / V8 ENGINE MANAGEMENT has to say (apologies for shouting):
"Misfire Detection / CAN Data
The ECM is able to detect misfire by monitoring crankshaft acceleration (CKPS signal). In order to reduce the possibility
of false misfire diagnosis, the ECM uses the ABS/TCCM CAN data – left and right rear wheel speeds – to
determine if the vehicle is operating on a rough road."
without splitting hairs, I can safely say in this case one cannot equate acceleration differences between cylinders with rpm.
A minuscule variation in acceleration, AKA “cylinder pressure” will not affect rpm by even 1 rpm between cylinders, or fraction there of, as long as the piston / connecting rod assembly is sill connected to the crankshaft.
And variation in rpm is what was asserted in earlier post # 99. Just trying to keep the meaning of words firmly established so there’s no misunderstandings.
Peter David Hill
, Mechanical engineer. Answered 1 year ago · Author has 1.8K answers and 1.9M answer viewsThere are 2 main ways to detect misfiring.
First is flame plasma rectification. This uses a DC voltage at the spark plug of 400v. If there is pre-ignition the voltage is shunted from the plug tip through the conductive flame to the cylinder head ground. If the spark fails to ignite the mixture then the 400v is not shunted to ground.
The other way to detect misfiring is by measuring the change of crank angular speed during each cycle. As the piston compresses the mixture the crank slows down, after ignition and TDC it accelerates. A pre-ignition will not accelerate the crank the same amount as a proper ignition. Failure to ignite the mixture will result in the crank slowing down for that cycle.
In both cases the engine management knows which cylinder it was firing on from the crank angle sensor.
I keep going back to what the car thinks is wrong. My apologies if this post is long, but I want to include my reasoning.
When everything is working properly, the ECM will send a ‘coil fire’ instruction to each ignition module at the correct point in the relevant cylinder’s cycle. If the coil successfully creates a spark, it will send a ‘spark OK’ confirmation pulse back to the ECM. All is good, and on to the next cylinder.
However, if the ECM detects a problem, it will throw a P035x code. For example: P0351 “Ignition coil (A1) primary /secondary circuit malfunction” (my emphasis)
My interpretation of the 'monitoring conditions' is that the ECM will allow a period of time (~5) seconds for the motor to settle down after start before it acts on any abnormal input(s).
The ECM will then take the default actions stated. Note default actions include:
Inhibit closed loop for the bank
Inhibit individual cylinder fuel injection
So, if the codes are correct, then possibly:
No ‘coil fire’ command is reaching the ignition module
There is no confirmation pulse being generated by the affected cylinders
The ECM isn’t seeing the confirmation pulse
The ECM isn’t responding correctly
Assume an idle speed of 690 rpm. That is 690/60 = 11.5 revolutions per second. Each cylinder fires every alternate cycle, therefore 11.5/2 = 5.75 times per second (5.75 Hz).
So it should be possible to measure the frequency of the pulses on:
i) the ‘coil fire’ connection (module pin 3), and
ii) the ‘injector fire’ connection (injector pin 2).
Both should be at 5.75 Hz.
Each time the ignition module successfully generates a spark, it will create a confirmation pulse for the ECM. The output pulse from each one is also at 5.75 Hz.
These outputs are combined into two groups of four, so the signal for each group sent back to the ECM will be 5.75 x 4 = 23 Hz. This is identified here in the EG on pin assignment for the ECM:
Note that the ignition module feedback groups are not one for each bank, but for two cylinders in each bank, hence
(1A 2B 3B 4A) and (1B 2A 3A 4B)
Your car is reporting P0353, P0355 and P0358.
P0353 is A3
P0355 is B1
P0358 is B4
…which are all within the same ignition module feedback group. Both banks, so no CL on either.
Ignition Modules
I’ve re-used the 99 diagram so the colours will tally with your car. Each coil primary is connected to B+ via pin 4 to the ignition relay. To fire the coil, the ECM will ground pin 3 momentarily at the correct time in the cycle, at a frequency of 5.75 Hz (idle).
IGNITION COILS
The confirmation pulses from pin 2 on each ignition module are combined at PIS11 and PIS12, then forwarded to the ECM. Each module produces a pulse at 5.75 Hz, hence an aggregate of 23 Hz at each splice.
Injectors
Each injector solenoid is connected to B+ via pin 2 to the relay. To fire an injector, the ECM will ground pin 1 momentarily at the appropriate time. This will happen every alternate cycle, so each of the 8 wires from the ECM to the injectors will carry a ground pulse at 5.75 Hz (idle) if all is well. If the ECM has inhibited an injector, then I would expect to see 0Hz on pin1
I've used the 99 wiring so it corresponds to your car.
The checks that need to be done are:
1) Measure the ‘coil fire’ signal from the ECM on pin 3 of the ignition module for each affected cylinders. It should read a frequency of 5.75 Hz.
2) Measure the ‘injector’ fire signal from the ECM on pin 2 of the injector associated with each suspect cylinder. It should also read a frequency of 5.75 Hz.
3) Measure the confirmation pulse aggregates at splices PIS11 and PIS12. (Alternatively, you could try any of the slate/[light]green connections at pin 2 of the module). Each one should report a frequency of 23 Hz.If that's fine, then repeat the check at EM83-10 and EM83-11 to confirm continuity
I used my multimeter and a long needle to get to the connections. Here’s what I did for the injector. Other lead to ground:
and the multimeter reading at idle:
Note the 5.75 Hz is approximate, and dependent on the exact idle speed. 5.83 Hz is fine.
Last edited by michaelh; Mar 14, 2022 at 02:10 PM.
"If driveshaft is out of balance or damaged, crank angle sensor might pick up on these vibrations. This can
suspend misfire monitor testing and prevent monitor from completing emissions monitor test. If you have a
vehicle with random misfire codes but no detectable misfires, have driveshaft balance checked."
Chances are very slim this is the issue but it indicative of how sensitive the electronics can be. I'm sort of surprised there haven't been warnings for damaged/out of balance/low pressure wheels & tires. Clearing the codes would give it a fresh start anyways.
I keep going back to what the car thinks is wrong. My apologies if this post is long, but I want to include my reasoning.
When everything is working properly, the ECM will send a ‘coil fire’ instruction to each ignition module at the correct point in the relevant cylinder’s cycle. If the coil successfully creates a spark, it will send a ‘spark OK’ confirmation pulse back to the ECM. All is good, and on to the next cylinder.
However, if the ECM detects a problem, it will throw a P035x code. For example: P0351 “Ignition coil (A1) primary /secondary circuit malfunction” (my emphasis)
My interpretation of the 'monitoring conditions' is that the ECM will allow a period of time (~5) seconds for the motor to settle down after start before it acts on any abnormal input(s).
The ECM will then take the default actions stated. Note default actions include:
Inhibit closed loop for the bank
Inhibit individual cylinder fuel injection
So, if the codes are correct, then possibly:
No ‘coil fire’ command is reaching the ignition module
There is no confirmation pulse being generated by the affected cylinders
The ECM isn’t seeing the confirmation pulse
The ECM isn’t responding correctly
Assume an idle speed of 690 rpm. That is 690/60 = 11.5 revolutions per second. Each cylinder fires every alternate cycle, therefore 11.5/2 = 5.75 times per second (5.75 Hz).
So it should be possible to measure the frequency of the pulses on:
i) the ‘coil fire’ connection (module pin 3), and
ii) the ‘injector fire’ connection (injector pin 2).
Both should be at 5.75 Hz.
Each time the ignition module successfully generates a spark, it will create a confirmation pulse for the ECM. The output pulse from each one is also at 5.75 Hz.
These outputs are combined into two groups of four, so the signal for each group sent back to the ECM will be 5.75 x 4 = 23 Hz. This is identified here in the EG on pin assignment for the ECM:
Note that the ignition module feedback groups are not one for each bank, but for two cylinders in each bank, hence
(1A 2B 3B 4A) and (1B 2A 3A 4B)
Your car is reporting P0353, P0355 and P0358.
P0353 is A3
P0355 is B1
P0358 is B4
…which are all within the same ignition module feedback group. Both banks, so no CL on either.
Ignition Modules
I’ve re-used the 99 diagram so the colours will tally with your car. Each coil primary is connected to B+ via pin 4 to the ignition relay. To fire the coil, the ECM will ground pin 3 momentarily at the correct time in the cycle, at a frequency of 5.75 Hz (idle).
IGNITION COILS
The confirmation pulses from pin 2 on each ignition module are combined at PIS11 and PIS12, then forwarded to the ECM. Each module produces a pulse at 5.75 Hz, hence an aggregate of 23 Hz at each splice.
Injectors
Each injector solenoid is connected to B+ via pin 2 to the relay. To fire an injector, the ECM will ground pin 1 momentarily at the appropriate time. This will happen every alternate cycle, so each of the 8 wires from the ECM to the injectors will carry a ground pulse at 5.75 Hz (idle) if all is well. If the ECM has inhibited an injector, then I would expect to see 0Hz on pin1
I've used the 99 wiring so it corresponds to your car.
The checks that need to be done are:
1) Measure the ‘coil fire’ signal from the ECM on pin 3 of the ignition module for each affected cylinders. It should read a frequency of 5.75 Hz.
2) Measure the ‘injector’ fire signal from the ECM on pin 2 of the injector associated with each suspect cylinder. It should also read a frequency of 5.75 Hz.
3) Measure the confirmation pulse aggregates at splices PIS11 and PIS12. (Alternatively, you could try any of the slate/[light]green connections at pin 2 of the module). Each one should report a frequency of 23 Hz.If that's fine, then repeat the check at EM83-10 and EM83-11 to confirm continuity
I used my multimeter and a long needle to get to the connections. Here’s what I did for the injector. Other lead to ground:
and the multimeter reading at idle:
Note the 5.75 Hz is approximate, and dependent on the exact idle speed. 5.83 Hz is fine.
Yikes. Great info. When I have some time I will try this. Hopefully I'll be able to do the measurements correctly.
What's the plug gap? I've seen a spec for the 2000 Normally Aspirated at 1-1.1mm (~0.039-0.043").
For a test, drop the gap way down, like 0.025" and see what it does. It may provide more consistent firing but more importantly, improve the misfire feedback circuit. Obviously, if you like what you see, gap it wider as time goes on or go back to original if no improvement.
A "relatively" lower compression engine could stand a smaller gap and go a tad hotter, but plug heat isn't a factor at the moment. I wouldn't deviate from the original plug as plug resistance matters.
I keep going back to what the car thinks is wrong. My apologies if this post is long, but I want to include my reasoning.
When everything is working properly, the ECM will send a ‘coil fire’ instruction to each ignition module at the correct point in the relevant cylinder’s cycle. If the coil successfully creates a spark, it will send a ‘spark OK’ confirmation pulse back to the ECM. All is good, and on to the next cylinder.
However, if the ECM detects a problem, it will throw a P035x code. For example: P0351 “Ignition coil (A1) primary /secondary circuit malfunction” (my emphasis)
My interpretation of the 'monitoring conditions' is that the ECM will allow a period of time (~5) seconds for the motor to settle down after start before it acts on any abnormal input(s).
The ECM will then take the default actions stated. Note default actions include:
Inhibit closed loop for the bank
Inhibit individual cylinder fuel injection
So, if the codes are correct, then possibly:
No ‘coil fire’ command is reaching the ignition module
There is no confirmation pulse being generated by the affected cylinders
The ECM isn’t seeing the confirmation pulse
The ECM isn’t responding correctly
Assume an idle speed of 690 rpm. That is 690/60 = 11.5 revolutions per second. Each cylinder fires every alternate cycle, therefore 11.5/2 = 5.75 times per second (5.75 Hz).
So it should be possible to measure the frequency of the pulses on:
i) the ‘coil fire’ connection (module pin 3), and
ii) the ‘injector fire’ connection (injector pin 2).
Both should be at 5.75 Hz.
Each time the ignition module successfully generates a spark, it will create a confirmation pulse for the ECM. The output pulse from each one is also at 5.75 Hz.
These outputs are combined into two groups of four, so the signal for each group sent back to the ECM will be 5.75 x 4 = 23 Hz. This is identified here in the EG on pin assignment for the ECM:
Note that the ignition module feedback groups are not one for each bank, but for two cylinders in each bank, hence
(1A 2B 3B 4A) and (1B 2A 3A 4B)
Your car is reporting P0353, P0355 and P0358.
P0353 is A3
P0355 is B1
P0358 is B4
…which are all within the same ignition module feedback group. Both banks, so no CL on either.
Ignition Modules
I’ve re-used the 99 diagram so the colours will tally with your car. Each coil primary is connected to B+ via pin 4 to the ignition relay. To fire the coil, the ECM will ground pin 3 momentarily at the correct time in the cycle, at a frequency of 5.75 Hz (idle).
IGNITION COILS
The confirmation pulses from pin 2 on each ignition module are combined at PIS11 and PIS12, then forwarded to the ECM. Each module produces a pulse at 5.75 Hz, hence an aggregate of 23 Hz at each splice.
Injectors
Each injector solenoid is connected to B+ via pin 2 to the relay. To fire an injector, the ECM will ground pin 1 momentarily at the appropriate time. This will happen every alternate cycle, so each of the 8 wires from the ECM to the injectors will carry a ground pulse at 5.75 Hz (idle) if all is well. If the ECM has inhibited an injector, then I would expect to see 0Hz on pin1
I've used the 99 wiring so it corresponds to your car.
The checks that need to be done are:
1) Measure the ‘coil fire’ signal from the ECM on pin 3 of the ignition module for each affected cylinders. It should read a frequency of 5.75 Hz.
2) Measure the ‘injector’ fire signal from the ECM on pin 2 of the injector associated with each suspect cylinder. It should also read a frequency of 5.75 Hz.
3) Measure the confirmation pulse aggregates at splices PIS11 and PIS12. (Alternatively, you could try any of the slate/[light]green connections at pin 2 of the module). Each one should report a frequency of 23 Hz.If that's fine, then repeat the check at EM83-10 and EM83-11 to confirm continuity
I used my multimeter and a long needle to get to the connections. Here’s what I did for the injector. Other lead to ground:
and the multimeter reading at idle:
Note the 5.75 Hz is approximate, and dependent on the exact idle speed. 5.83 Hz is fine.
Wow Michael! Brilliant and way above my head, but your explanations are so good, I think I get some of it! Amazing...
I'll keep listening and learning in this thread. Thank you!
Since moving to Florida from Connecticut, we have friends and family visiting a lot. I have a house full for the next two weeks so my work time on the car will be curtailed. I will get back to it as soon as possible. Even though the car is undriveable, it does look good sitting in the garage
without splitting hairs, I can safely say in this case one cannot equate acceleration differences between cylinders with rpm.
A minuscule variation in acceleration, AKA “cylinder pressure” will not affect rpm by even 1 rpm between cylinders, or fraction there of, as long as the piston / connecting rod assembly is sill connected to the crankshaft.
But - RPM is one convenient unit of measurement we use to express angular speed/velocity:- they are the same thing. If av decreases momentarily due to a misfire, even by the minute fraction required to detect it, then that cycle will take slightly longer to complete and RPM must be lower.
It may be the difference between 600 rpm and 599.991 rpm, but there must be a correlation.
Last edited by michaelh; Mar 18, 2022 at 03:24 PM.
But - RPM is one convenient unit of measurement we use to express angular speed/velocity:- they are the same thing. If av decreases momentarily due to a misfire, even by the minute fraction required to detect it, then that cycle will take slightly longer to complete and RPM must be lower.
It may be the difference between 600 rpm and 599.991 rpm, but there must be a correlation.
the post I found an objection to referred to rpm differences between cylinders. That cannot happen.
What you describe, to paraphrase, a reduction in overall rpm, certainly can happen and is likely what is being measured..
Are you guys saying that there can be an RPM change as the firing timing is off? The reason I ask is, the car does do this weird idle RPM change. Every 5 to 10 seconds there is almost a click sound and the idle speed will change.
Last set of visitors left yesterday. I'm going to catch my breath and start back on this in the next couple of days. I have to admit that not working on the jag for a couple of weeks has been relaxing. I have done work on our other cars as they are needed for transportation. Our XK8 which my wife has named Jerome, just looks good sitting in the garage.
Ok, I'm not sure what I'm doing wrong. The Hz readings I get are all over the place. It jumps from a low of 160 to a high of 600 with a lot of different readings in between. When I switch the multimeter to mA, I then get readings between 5 to 5.8. Checking the slate, pin 2 wires, I then get the same numbers jumping all over the place.
