(Sorry so jumbled, trying to remember everything done so far)

At my work, we've had this 92 Lesaber, 3.8L n/a, that has been a real pain. Came in a few weeks ago for a no start, we replace the crank sensor (after testing of course), and all is good. Then it came back in last week because it was running terrible. It was only running on four cylinders and the middle coil wasn't firing. I swapped it with the one about it, and that one wouldn't fire,. The ICM was not giving a ground signal to that particular coil, so we replaced the ICM and test drove and all was good.

It comes back again the next day, same problem, but only when warm and drives fine when cold. Everything pointed to the icm bad in the same spot, so we assumed a defective ICM (we've had problems with napa ICM'*). The new one didn't fix it.

At this point we were confused, Coils seemed ok, but we thought maybe the middle coil was overheating the middle circuit on the icm when warm. So we swaped them when cold and after it warmed up the middle one still wouldn't fire.

Running outta options we took the icm and all 3 coils (known good parts) from my 94 sse, and it ran great untill it warmed up, then same thing, the middle coil wasn't firing.

Now were at a stand still, as of now we checked wiring diagrams and found no possible way that the pcm could shut down just one coil. We scoped 3x and 18x crank signals for the cranshaft sensor while it was missing and even chased all wires to see if they have rubbed through anywhere and everything seems to look good (were not a 100% sure on the 18x signal,)

The customer is being very patient, but we'd like to get this car moving soon, does anyone have any ideas and much thanks to any help

Moved to 1992 - 1999 section. Problems with a Buick Lesabre now belong in this section.

How sure are you the middle coil isn't getting the ground signal?? How are you testing for that?

If all you really saw was the coill NOT firing and being this is a spark waste system, have you replaced the wires and plugs for those 2 cylinders? The spark actually travels thru the first plug, into the block, across the opposite plug, and back to the coil thru the other plug wire. I could see heat causing problems in the complete path of the spark.

both a power probe and a test light

Any chance the rings on the harmonic balancer could be bent?
How did you center the crank sensor?

we tested it with a lab scope, we are leaning towards a problem with the balancer or the sensor because we are unsure of the 18x signal, it almost looks like something is missing, but it could just be the marking for number one cylinder, aldata doesn't give a clear picture of a crank singnal pattern so were gonna test it again tommorrow while its cold and compare it to when it is hot , and i just marked where the sensor was and put the new one back in the same place as the old one


If it is a problem with the crank sensor or tone ring, though, wouldn't it do it all the time and not just when its up to temp

I'm wondering if the sensor position could change by a few thousands due to thermal expansion. This little bit of movement may be enough if the sensor isn't centered properly. Just a theory, I don't believe we've seen this problem before.

were going to lab scope the sensor again today while the engine is cold and running good and see how it compares to the engine hot and running bad. I'll keep you updated at my luch break around noon if we've tested it by then

Do you have a dual trace scope where you can look at the 3x and 18x signal at the same time, and compare the pulses and timing of them?

Could it just be a dirty ICM harness?