: 99 deville with a missfire



scrap
01-24-07, 08:14 PM
I have a missfire that I cant seem to find the problem with.
This is what I have done so far. Changed plugs, wires, coils, ignition module, injectors. Checked compression was good. smoked the motor for any intake leaks without finding anything, pulled the vavle cover and checked the cam lobes and also checked to make sure the valves were opening and closing, checked vavle springs and looked good. After that I pulled the intake off just incase we missed something. Didnt find any problems and reinstalled that with new gaskets. The problem is still there and is only on cylinder 6. I notice it more just at idle seems to go away with more fuel. I've searched on the forum here for a bit and the only thing I found that I havnt tried was a ground cable going to the coil pack. Also metion there are no codes.

Ranger
01-24-07, 09:01 PM
Are you sure #6 injector is pulsing?

scrap
01-24-07, 09:21 PM
Are you sure #6 injector is pulsing?

Yes I've checked that with a noid light. also have done a injector balance test.

eldorado1
01-24-07, 09:25 PM
Check spark plug hole for water or oil accumulation and clean if necessary

Also try a leak down test. Could be an early head gasket, especially if that cylinder's plug was cleaner than the others.

Ranger
01-24-07, 10:12 PM
I didn't want to be the first to say the "H" word, but seems like you have checked everything else. Might as well rule that out.

scrap
01-24-07, 10:39 PM
I didn't want to be the first to say the "H" word, but seems like you have checked everything else. Might as well rule that out.

I have been thinking that but I have good compression. I guess I'll do some more tests for that tomorrow.. just thought I might be missing something stupid/simple.

eldorado1
01-24-07, 10:47 PM
good compression does not rule out a head gasket leak

Ranger
01-25-07, 05:23 PM
Right, head gaskets can be shot and leaking like a sieve and you'll still have good compression. Do a cylinder pressure test to verify it.