Sometimes when 'power' electronics goes bad it will break into oscillation instead
of just suddenly quitting. I have a couple of questions:
Q1: Once the engine stalls and the injector(s) are still chattering, if you turn the
key from ON to OFF and back to ON again, will the chattering continue, or will
it cease?
Q2: Assuming that the chattering in Q1 continues across a power cycle, I would
be interested if you could do the following: Malfunction occurs, engine stops,
injectors still chattering, turn key to OFF, pull the plug to the ICM, turn the
key back ON, and then what happens? Our 2 choices would be:
* Chattering stops. Assumption that ICM was the one that broke into oscillation
and was sending spurious signals up to ECM.
* Chattering continues. Since there's no stimulus from the ICM, this would tell
me that the ECM is the component that is breaking into oscillation?
Disclaimer: The GMT400 in my driveway is a Vortec, which is different than a TBI setup. So
I'm having to rely purely upon the TBI section in the older FSMs for troubleshooting approaches.
But the more we learn about your failure before you replace a part the more info that
others can learn from. (In English, I am living vicariously through your real-world
troubleshooting. :0) Seriously, Schurkey's comment about another member having
a similar issue and it was the Ignition Control Module makes sense to me.
Anyway, I would be interested if cycling the power changes the behavior, or does the
suspect circuit just break into oscillation and stays out of control for some period of
time before recovering? BTW, I appreciate the fact that you are trying to take the time
to understand this instead of just shoveling parts at it.