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1998 Pontiac Bonneville SSEi cylinder misfire
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Troxartes
New User
Aug 20, 2008, 6:46 PM
Post #1 of 4
(5018 views)
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1998 Pontiac Bonneville SSEi cylinder misfire
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Hello everyone, I'm hoping you can help me with a problem on my Bonneville.
The computer scanner showed the code for #6 cylinder misfire. The car sounds great up until 4000 RPM, at which time it starts to miss badly. It won't go past 4000 RPM and the boost gauge stops at 0. I changed all the spark plugs, and the problem persisted. I changed the 3-6 coil, problem still there. I changed out the ICM, the problem is still there. I've made sure the 6 wire is nowhere near the O2 wire. I've had a couple of guys tell me about coolant leaks from faulty LIM gaskets, but it's the opinion of myself and my father and brother, both mechanics, after observation, that the LIM gaskets are not the issue. My brother seems to think it has something to do with the fuel injection system. My father thinks it might be an issue involving the computer itself.
Also, we tested the 3 and 6 wire to see if that was the problem, but it proved not to be. Using a timing light, BOTH the 3 and the 6 cylinders showed misfiring, with the 6 barely firing on idle.
Any ideas? I'm desperate because I go back to school in a few days and need my car badly!
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Jeff Norfolk
Enthusiast
Aug 20, 2008, 8:00 PM
Post #2 of 4
(5014 views)
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Re: 1998 Pontiac Bonneville SSEi cylinder misfire
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The two guys that told you about the leaky intake problem were right. This car and other GM products around this year are very problematic in this area. Although it is odd that it only shows up at 4000 RPM. Run a cooling system pressure test Look for leaks. If none are found externally then look in the oil fill hole for oil/coolant mixing. It will show up here before the dipstick. If this is the problem it is a relatively easy repair for experienced techs. Good Luck.
Jeff
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Troxartes
New User
Aug 20, 2008, 8:11 PM
Post #3 of 4
(5013 views)
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Re: 1998 Pontiac Bonneville SSEi cylinder misfire
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Thanks for the reply! I guess I'm a little confused.....we've verified with the computer scanner and the timing light that cylinder six is misfiring. Exactly how does a coolant leak effect the cylinder misfire? The computer says clearly it is a "Cylinder six misfire". We're thinking it is the computer (ECM) because it controls the firing signals. Is there a code for a leaking manifold? It just seems to be more of an electrical problem than a simple leak.
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Jeff Norfolk
Enthusiast
Aug 20, 2008, 8:39 PM
Post #4 of 4
(5012 views)
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Re: 1998 Pontiac Bonneville SSEi cylinder misfire
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There is no code for coolant leak. If the coolant is leaking thought the intake manifold gasket at the #6 cylinder than it will be trying to burn coolant along with fuel causing misfire.
Jeff
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