very bad misfire under load (93 SE) (SHES ALIVE!) - 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 09-03-2007, 11:34 PM   #1
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Default very bad misfire under load (93 SE) (SHES ALIVE!)

My 93 SE is falling apart. 3 breakdowns in 2 weeks. Last night I cleaned the engine (alternator was removed, coils&icm covered, intake covered), swapped the trans mount again (replacement broke in a different spot), and changed the belt. When I put everything back together this afternoon, I had a horrible misfire under load. First I checked the coil resistance, and all 3 secondaries were good, but the primaries seemed a tad high with all of them at 1.1. It doesnt matter what your in (park or drive), it runs rough under any type of load. If you are cruising it runs fine, but under load it shakes and bucks bad. You can hear an audible miss out the exhuast and the smell of raw fuel is there. Scantool shows no codes, and the car is running very rich. It is also very slow. Could one of the coil packs be bad even though they read good? The car was running good till i sprayed it down. What should I do? I was thinking take the coils and icm to autozone and have them check it, along with checking the resistance of the wires myself. I might also pick up a coil from the junkyard to test it out. Any other ideas?

Thanks,
Andrew
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Old 09-04-2007, 10:22 AM   #2
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I would start with the simple (and free) stuff first. First question to ask is: What did I take apart, and did I put it back properly? All the wires to the alternator tight and right? Did you remove plug wires? Any other wiring? Is the firing order correct? Good ground on ICM?

If you removed either end of plug wires: Plug wires can break internally causing a miss when they are removed from the plugs or coils. If it has been a while since plugs and wires have been changed, I would replace those first.
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Old 09-04-2007, 10:25 AM   #3
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what type of plugs are they? TR-55'*?
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Old 09-04-2007, 11:26 AM   #4
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Don't waste your time taking the ICM or coils to be tested. Those testers are a joke. Good units test bad, and bad test good. It'* a coin-flip.

Check your coils with a different meter. Both hot and cold. (warm them up in the oven if you have to....150 degrees or so).

Check the ICM connector. Consider disconnecting it and spraying it out with WD-40 to displace any moisture that may be in there (WD stands for Water Displacing, which is what it actually is.....NOT a lubricant).

Start the car and let it idle at night. Spray it with a light mist of water in the dark and look for plug wire arcs.
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Old 09-04-2007, 11:55 AM   #5
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My opinion is that you may have crossed a couple wires. Sounds just like it. Although you don't mention removing the wires. Or you got water into something electrical and it'* sitting there.

Do you have an air compressor and blow gun? If so..blow off the coils..double check all your wiring connections.
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Old 09-04-2007, 11:50 PM   #6
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Today'* update....I'm ready to sell this car. Its been nothing but trouble for 3 weeks straight.

The real update is when the engine heats up under load, it starts misfiring. If I let the car set off for about 10 minutes, then crank it and drive it, I can WOT with no misfires. But, as soon as that run is over, the misfires are back. I'm thinking plugs/wires. I bought one new coil today, and swapped it in every spot just to check if 1 was bad, but no luck. Can anybody give me a proper wiring diagram. I found one from autozone'* website but I'm not sure its right. Any other ideas?
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Old 09-05-2007, 03:11 AM   #7
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................Firewall

-------2--------4--------6......Rear Bank


6... C
3... O
2.... I
5.... L
4.... *
1
-----1--------3--------5....Front Bank

....................Radiator
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Old 09-05-2007, 08:09 PM   #8
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Well i took the car to a mechcanic today. I replaced the plugs and wires, tested the coils, swapped a new coil trying to find a bad one, cleaned all the plugs, checked the ICM connector, scanned the car for codes, monitored the sensors, and more. Still no luck. I dont have anything to test the fuel system with, so I couldnt do that. Hopefully the shop will figure out what is wrong quickly. Its my daily driver, and my family doesnt have an extra vehicle. My car usually serves as there backup vehicle since I'm the youngest. Being carless sucks.
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Old 09-05-2007, 10:23 PM   #9
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Being car-less sux, but you still have a cool sig pic.

Keep us posted. Check with the shop daily and let us know.
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Old 09-05-2007, 11:15 PM   #10
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They said they should be able to let us know something by tomorrow. The same shop has worked on the car since we quit going to the stealership years ago. The odd thing is that the car only screws up when its in closed loop. I think its fuel related aka pump or regulator. The filter is pretty new.
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