Just for fun, I thought you guys might like to have a look at the car. All in all it'* not in bad shape for being 25+ years old. Everything works except the speedo and the front windows (needs new window motors, that'* the next thing.) It'd be a great second car if I could just solve this little intermittent problem!

Thanks, I found it!

http://padgett.performanceresearch.us/coils.htm



Yep, I'm gonna try to do this in the next few days.

Here'* some info on checking cps, etc.

Joel

http://easyautodiagnostics.com/gm/3....-sensor-test-1

Okay, today I swapped the ignition to the Delco type, and it still misses. But I think I'm on the right track. The missing seems to happen faster now and it stutters more violently sooner. The engine also seems to stall between misses now when at WOT. So, ICM or coils?

The swap should have involved the ICM and coils.

I would want to check to confirm the CPS is behaving as it should at this point.

I posted the last reply from my phone. I was in a hurry and didn't include all the information, so here goes. One upside with the Delco ignition is that the car (when running correctly) idles much smoother than it did with the old Magnavox ignition. The throttle seems to be moderately more responsive, and it seems to have more pickup. It definitely hesitates less when you floor it.

Let"* talk about the misfire problem. When the problem began to occur with the new ignition, it started to buck pretty bad right at the beginning when I gave it plenty of throttle. There may be an upside though, as this partial engine stall is totally new behavior. With the new ignition, it misses a few times plus it partially stalls in a somewhat rhythmic fashion. It will miss a few times, begin to stall, bounce back, miss a few more times, partially stall again, bounce back, and so on. So, it goes like this:


Interstate on-ramp > WOT > Engine RPMs begin to rise normally > miss > RPMs rise > miss > RPMs rise > partial stall for about a second > RPMs rise > miss > RPMs rise > miss > partial stall for about a second. It seems to repeat. All of this would be happening in maybe 5-10 seconds of WOT.

So, maybe this means I'm on the right track? Maybe it'* possible that the junkyard ICM or coils I got today have the same problem the old ignition was having?

To reiterate, with the old ignition at WOT it would just stutter and miss in a somewhat rhythmic fashion. The stuttering from the misfire would become more pronounced the longer the car is running, but the engine has never stalled when this problem was happening before.

And just like before, after sitting for an hour the car fired right up and ran perfectly on the return trip.

So, do you guys think it'*... bad Delco ICM? One or more bad coils? ICM connector plug, even? Or should I start looking at the fuel pump?

Yes, I swapped the mounting plate, ICM, and coils. Mounting plate came from a '95 LeSabre 3800, the ICM and coils came from a newer 3800 (it does seem like they changed the plate design after '95, it was different on the '96 I looked at.)

It'* worth mentioning that I had to try two ICMs. On the first ICM, the engine would start but it ran really bad and knocked when throttle was applied. It sounded like a couple of cylinders weren't firing. Second ICM, car cranked right up and it runs smooth.

But ... wouldn't the engine not be starting if that sensor was the problem?

At one point you said that upon starting the engine rpm would rush to 2000 rpm. If you have a multi-meter a quick check of the tps would rule out that sensor.

I do have one and I can, how do I check it exactly?

Just for reference, that high idle after start has only occurred four or five times out of maybe 75-100 times cranking up the car over the past couple of weeks. When it did happen, I turned the engine off and immediately started it again, then it would idle normally. I just assume it'* related, maybe not.

I was thinking perhaps that there is an intermittent failure of the sensor, or associated wiring, however, admittedly that would be a failure never seen before. I would think that if this was the case however, you would likely show engine rpms drop to zero when the issue is popping up (especially during the 'stall), at least you would, if you had one.

It would also be good to check fuel pressure at this point too. The 'stall' could also be an indication of a fuel delivery issue, which would be apparent when you throw a gauge on it.

I am not sure how else to proceed at this point, because everything I can think to do next involves plugging a scanner in to the car and reading live data.