Any GM Techs?

[MoeBawlz]

Is anyone on here a GM tech? I have a problem with a 01 Monte Carlo that is driving me insane. If anyone is willing to let me pick their brain please let me know. Thanks in advance.

[mone]

Yea I worked for GMC for 5 years ..how may I help you??

[MoeBawlz]

Excellent maybe you can help me to figure out what the heck is going on with this damn thing. So I have a random missfire and it also dies once in a while at random times, but only when warm. Been through a lot of headaches with this thing and the thing im confused on is the 3X and 18X signals comming off the CKP. I understand that the 3X is for lower rpm and cranking trigger for the ignition, and 18X is for upper rpm ignition. But when looking at a scan tool they should both follow the rpm. So as the rpm rises the 3X and 18X counts both rise to a very close number to the rpm.

If im mistaken on this please let me know. When looking at the two numbers the 3X follows the RPM all the way up, but the 18X stops at about 1600 counts and will not go any higher. I wasnt sure if this was normal or not, looked through mitchell on demand and got no where with that.

If you have any thoughts on this please let me know. Thanks in advance

[MonzaRacer]

Ok here is what alldata has on it:
Three dual tower ignition coils are mounted to the IC module, and are serviced individually. The IC module performs the following functions:


It supplies a power and low reference circuit to the CMP and CKP sensors
It receives and processes the signals generated by the CMP and CKP sensors
It determines the correct coil triggering sequence, based on how many 18X ON-OFF pulses occur during a sync pulse. This coil sequencing occurs at start-up, and is remembered by the IC module. After the engine is running, the module will continue to trigger the coils without the CKP input.
It determines the correct direction of the crankshaft rotation, and cuts spark and fuel delivery to prevent damage from backfiring if reverse rotation is detected.
It sends 18X and 3X reference signals to the PCM
The 3X reference signal is also known as the low resolution engine speed signal. This signal is generated by the IC module using an internal divide-by-six circuit. This circuit divides the 18X signal pulses by six. This divider circuit will not begin operation without a sync pulse present at start-up, and without 18X and 3X reference signals no fuel injection will occur
Now what you have is most of the signal conditioning is done by the ignition module so the computer gets what it wants.
As for a misfire I would look at the secondary ingition ,EGR, and possibly even the plastic upper plenum (since you listed signal references for a 3.8 and not a 3.4) leaking either vacuum(very unlikely ) or antifreeze internally.
another thing is make sure you have the proper spark plugs as most new current OBD2 cars dont like anything but what they were designed to run with.
Anotherthing to remember is that the car is going to be VERY sensitive to a resricted fuel filter and/or bad/weak fuel pump.
AS for diagnosing an intermittant misfire takes a good high end scanner and some good current diag skills/training.
I do it for a living and have around $10k of tools just to diag cars (and this isnt counting just general tools either) and still need more.
The big thing to remember is that because it needs to properly time for each tooth so it can detect misfires and so it needed to be cut back for the computer to read cleaner AND they didnt want to go back to multiple output sensor.
Good luck
Lee

[CamaroAJ]

I work at a Chevy dealer as well. i looked at SI and didn't see anything. do you have a code or anything? also does the car have an aftermarket alarm/keyless entry and/or remote start?

[mone]

Any new reports?How is the car doing?Check that fuel filter...