Running down a miss. - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 12-07-2007, 12:24 PM   #1
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Default Running down a miss.

Ok, I am a bit stumped. I have recently within the last 4 months replaced the plugs (TR55'*), Belden wires, Denso O2, upper and lower intake gaskets, pcv, BCS, swapped the BCA, replaced both belts, and added the Magnaflow cat. I have also swapped around coilpacks with three JY ones I have, cleaned the ICM, and checked a few times for vacume leaks. I still have a miss that is a bit of a rough idle and the bucking in 4th and lockup. It seems to be gradually getting just a little more bucking as time goes on. Any advice on what else to try? Maybe the ICM, or PCM?
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Old 12-07-2007, 12:31 PM   #2
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#1: Check your coil packs using the procedure in Techinfo.

#2 Pull all 6 plugs and keep them in order. Number them, take a pic, and post it here. This will help us find out if it'* random (air/fuel/low voltage) or cylinder specific (plug, wire, coil)

Things to look for:
Any plug wire touching metal. Shorts to dipstick tubes, alternator brace, manifold, etc can be VERY hard to see. Usually evident by a TINY little gray or black mark on the wire. Easier to find at night by misting some water (in the dark) over the wires/plugs/coils while the motor idles. Open wires as well, and they can be intermittent. Pull all 6 wires, and check their resistances. They should be evenly progressive based on length (lower resistance for #1, highest is #6, with a 'step' between front and rear). You check resistance while a frend bends and twists gently on the wire.
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Old 12-07-2007, 01:27 PM   #3
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Default miss

If all the electrical tests check out do a compression test on each cylinder. You may have a dirty valve hanging up.
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Old 12-07-2007, 03:24 PM   #4
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I had some of the same issues a while back. I ended up finding my #6 wire resting on my O2 sensor. I tie wrapped that up out of the way. There'* also a ground wire that has a ring crimped on it that is held on by the bolt and nut under the ICM. You might want to check that out as well.
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Old 12-07-2007, 10:32 PM   #5
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I had the same symptoms once when I had just replaced the plugs...the insulation was cracked on a plug so I must have overtightened it/got it at a weird angle. I had an audible misfire through the exhaust @ WOT and terrible bucking with light throttle in lockup.
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Old 12-08-2007, 02:20 AM   #6
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Guys, let'* not just throw out "it happened to me once, and I did this". Let'* actually go through the troubleshooting steps. Electrical misfires can be caused from 5 different things. 20% of us have experienced one of them. There'* no point in shotgunning coils, plugs, or wires. We can actually troubleshoot it, find the cause, and save some money for beer.
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Old 12-08-2007, 09:15 AM   #7
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Thanks for the replies and I will try all the things you mentioned Will as soon as it warms up a little and we get through the holidays. I still have to get a correct reading on the fuel pressure yet, but I am waiting for my almost 3 month belated B-day present from my sister-in-law who has a FP tester for me.
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