Usually what happens with these early ignition systems is the ignition control module (ICM) that the coils are mounted on top of starts to drop out the crank and sometimes cam signal to the PCM. This ICM is responsible for taking the cam and crank sensor signals, buffering them for the PCM and then send them on their way. PCM then tells the ICM what kind of ignition timing the engine needs and the ICM administers that.The Dark Side of Will wrote:In addition to getting started on the 2.5" stainless X-pipe exhaust that I realized I could fit, I swapped out a couple of coil packs.
The "ignition drops" I've mentioned before were getting pretty bad. The car was difficult to drive in higher gears below 2000 RPM under load and pretty much wouldn't pull cleanly from 1000 RPM in 4th or 5th.
I swapped out one of the two coil packs I had out in the shed. It was worse. In addition to ignition drops being at least as bad as the original coil pack, it also had a bad coil and dead miss. Bleh.
The second swapped pack was much better than either original or the first swapped pack in terms of ignition drops and did NOT have a miss. I left it installed. It seems to have ignition drops based more on time than anything. When I was out for the test drive, sometimes it would pull cleanly from 1000 RPM in 5th uphill and not have any problems until it had a cluster of 3 or 4 drops at 1800, then keep pulling. Sometimes it would have 2 or 3 drops at 1200, then keep going. Sometimes it would be clean all the way from 1000 to more than 2000.
The original coil pack wouldn't allow the engine to idle for more than a few seconds before an ignition drop stalled it. The current coil pack allowed the engine to idle for more than a minute when I got back from my test drive. During that period, it experienced a couple of ignition drops, but none of them stalled the engine.
I've never seen the ignition drops happen above 2000 RPM. An ignition drop, if you remember from earlier in this thread, is a momentary loss of ignition. I can be seen by a flicking of the tach, heard in the exhaust note and felt via a split-second power interruption. Since the power delivery is actually interrupted and the tach flickers, the problem must be either in the trigger signal path or power. The trigger signal starts at the crank sensors then goes to the coil pack (ICM) to be translated into something the ECM can understand as well as driving the ICM's tach output, which goes to the tach. Somewhere in that path is the problem.
I guess it *could* be something esoteric with the ECM, causing it to drop the coil trigger signal while keeping the bypass line active. Not sure how the ICM would react to that. I suspect that's a long shot because the tach is showing signs and it is driven by the ICM using crank sensor signals, not by the ECM.
Ideas?
I will bet either your signals(most likely crank) are getting lost either on their way to the ICM or in the ICM.
We have had plenty of ICM's cause drops outs in power as you are describing.