: Misfire Woes



cactuskid
06-16-04, 04:29 PM
95 Concours Deville 4.6l



This car had new plugs, wires, and the #3/8 coil replaced at 90,000 miles before I purchased it. Now at 125,000, the engine developed a slight misfire at idle and a more pronounced and consistent misfire under a load. I replaced the plugs, wires, and all for coil packs with new aftermarket products. In the process, I noticed that the #3/8 coil pack had severe carbon deposits on the contacts and inside the associated plug wires.



I started the engine and noticed no improvement. P085 was current. I checked the throttle body and plate and they are clean. The throttle position motor seems ok but although it makes some noise when doing a self check.



I removed the plugs and wires and reinstalled them with AC Delco parts. The engine still runs poorly. After a few hours, I noticed that the #3/8 coil was extremely hot. I removed it and found that the bottom of it had melted.



So, I the removed all of the coil packs and checked the primary voltage for each coil at the ignition control module. #3/8 shows battery voltage during key on, engine off and while cranking. All of the others show approximately .5 volts with key on, engine off, and about 3 volts while cranking.



Checking with an inductive timing light, I found that wires #7 and #8 fire occasionally. #2, #4, and #6 fire normally. #1, #3, and #5 fire intermittently. The wires are tight and definitely installed correctly. No loose wires or vacuum hoses. The exhaust smells rich (like raw gas) which makes sense with so many cylinders not firing correctly. No codes are current or in history. The car starts right up but lacks power when driving. I have ordered a new ignition control module from AC Delco with 4 new coils. What else am I missing? With no codes, all I can really do is change out parts. Maybe the PCM? Crank or cam sensors?



Thanks in advance!



Dave :hmm:

eldorado1
06-16-04, 05:34 PM
95 Concours Deville 4.6l
I removed the plugs and wires and reinstalled them with AC Delco parts. The engine still runs poorly. After a few hours, I noticed that the #3/8 coil was extremely hot. I removed it and found that the bottom of it had melted.
Good grief.. I think you found your problem right there. I would bet some of the output transistors in your ignition module shorted out... All 3 crank/cam sensors feed the ICM so it is very doubtful any of them are at fault. I think you're on the right track replacing the module and the coils. I'd bet that will solve your problem right there. Not sure why it didn't set any codes, isn't 95 OBDII????

Aurora By Olds
06-16-04, 08:49 PM
'95 is still OBD I, just with the II conector.

cadillacstars
06-16-04, 11:36 PM
'95 cadillacs are obd1, with an obd1 connector. '95 Auroras are obd1 with an obd2 connector. strange but true. obd1 systems like in your 95 do not have misfire counting capabilities, thus no codes to indicate misfire. Anyway, replace your module

cactuskid
06-25-04, 09:57 PM
:bouncy: Well, as it turns out it was the ignition control module. The module I bought came complete with all new coil packs. The interesting thing is that the new coil packs are numbered and arranged differently than the old coil packs and through trial and error I found out that you must connect the plug wires the way that they were orriginally wired and not according to the numbers on the new packs.