Question 2 from the following 3800 Buick Post
After you saw that there was a secondary misfire you went to the crank sensors, why?
First a look at the schematic….
The first clue was the CMP (cam sensor) performance DTC that was setting. I really don’t need all the gory DTC enable criteria to have an idea of what is happening. All I needed to know is what the PCM looks at to evaluate the CMP sensors performance. The PCM is watching the ratio of the 18x, 3x FC, and CMP signals. I do not bother with trying to remember all the possible DTCs that entails; that can change from vehicle to vehicle and year to year for the same 3800 engine. If the engine had run longer, it may have set a different DTC. It may have set an altogether different DTC instead of the P0341. It all depends on how the calibrator implemented the diagnostic sequence and what DTCs are available for that make/model.
Back to the point, what I DO KNOW is that the coils are mistriggering and that it appears to be RPM relative. If I let it sit and idle, it’s fine. If I raise the RPMs up, it starts backfiring as the coils fire out of time and sequence.
Could it be an ICM (ignition control module)? Sure, but is it likely? No, otherwise the backfiring and such would not likely be so RPM sensitive and the condition so repeatable. Could it be the CMP sensor? I don’t see how that could possibly be. It is all pointing to the 18x and 3x Sync signal out of the CKP sensor to the ICM. So that is where I looked first…. And was rewarded for my efforts <g>
Why didn't you go to EST first
to confirm your suspicions?
I hope I’ve answered that one. The P0341 was the clue.
Jim Wilson