: Front Bank Misfire

10-12-08, 08:18 PM
Just rebuilt a customers 97 deville and front bank cylinders are misfiring (2,4,6,8). Have changed EVERYTHING. injectors,o2,ICM,intake,PCM,Plugs,Wires, etc. Thought maybe the timing was off when the timing chain was reinstalled however another caddy engineer had said that it would have to be off by two teeth and would run for crap. The car runs great under load and only misfires at idle. Looking at the TechII it shows pulse width on front bank to be shorter than the back bank. Ive seen this in only two other threads on here and both having swapped engines previous to the problem. Anyone have ideas on this problem?

10-12-08, 08:59 PM
Check the plug wiring against the diagrams.

10-12-08, 10:05 PM
and what controls the pulse width? shouldn't the pulse widths be all the same for all cylinders at idle? it is sequential firing but are the pulses for each cylinder different? there is an o2 sensor for the front bank and rear bank. does the computer try and lean/richen out banks individually?

11-03-08, 12:03 PM
Found the problem. Turns out the AC compressor was in such bad shape that it was causing the knock sensor to think the engine was knocking. This is why the whole front bank was missfiring.

11-03-08, 01:15 PM
WoooHooo !!! That's one for the archive. Who'd a thunk it ???

11-03-08, 04:09 PM
Holy misfire Batman! We'd have never figured that one out.

11-03-08, 04:32 PM
Suppose one were to remove the knock sensor from the head/block (wherever), make a ground pigtail, insulate the sensor tip in a ball of silicone, stick the whole thing, connector and all, in a piece of foam pipe insulation and just let it lie in the valley. It must be connected because it senses sound frequencies to verify a signal.....(pipe plug in the hole.....)

Run the octane fuel that does not cause audible ping. The PCM would never sense knock, therefore would not pull timing. :eek:

11-05-08, 03:13 PM
Yeah as it was, my buddy was complaining about the noise (the compressor) so I shut off HVAC system to prove to him that it was the compressor and not the engine. I did this while the tech II was hooked up and on the misfire graphics. By this time I noticed it wasnt missing anymore and waited......and waited for another misfire. About a half hr later i kicked the HVAC back on thinking it was the only thing ive touched in that time and the miss came back when the compressor kicked on.