Random misfire/Cylinder 5 misfire.. tried alot.. help [Archive] - GrandAmGT.com Forum


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06-07-2012, 05:31 PM
Okay, ive been reading alot about the common SES blinking and misfires and stuff. Ive seen a few threads but it seems most threads dont end with a conclusion or peoples solutions.

I have a 03 GT. One day out of no where my car started bogging and runnning like junk and misfiring. I had blinking SES at one point. I read the codes and got 2.

Random misfire
Cylinder 5 misfire

Changed all the plugs, Cylinder 5 plug was all black and dirty looking. Rest were nice. Changed wires, coils, coil housing (ignition module). Ran some seafoam in the gastank and a splash in the crank case.

The SES blinking has stopped and seems to idle not too bad a little rough sometimes. When i rev it up past 2000rpm and let off it almost stalls.

Also when it was running today it smelt BAD like rotten eggs and sounds like sputtering out of the exhaust. Plugged up CAT? Car has 200,000km on it.

Compression test in front was 150~ on cylinder 5, i got 0, 150, 130, 110, 40, 50

Any ideas? Valve? Cat?

06-07-2012, 06:49 PM

06-07-2012, 07:47 PM
A busted head gasket and cat probably.

06-07-2012, 08:58 PM
I forgot i also get Catalyst performing below efficiency.. been getting that for awhile now. I just do not want to start tearing the engine apart if the cat is causing issues. But the cat would not affect compression right just other random misfiring.

06-07-2012, 09:01 PM
I'm not sure the cat will cause misfires or not. Someone with more knowledge on that would have to chime in. I was basing my guess from the compression reading you were getting and misfire codes.

06-07-2012, 11:45 PM
Ya i guess misfiring would cause cat damage.. Ive read alot of posts with these problems but never read their end fix.. We are gonna start ripping it apart i guess.

06-08-2012, 11:33 AM
No one else has any ideas?

06-08-2012, 11:39 AM
A cat can cause misfiring yes... Some symptoms of a clogged cat are exhaust fumes smelling like rotten eggs and the cat getting red hot. A cat is easier to change than a head gasket. There are stock replacement magnaflows available.

06-11-2012, 08:41 PM
Okay agreed. But a cat problem would not cause all cylinders except cylinder 5 to have low compression.. and varrying compression at that. from 30-150 on all the tests. We figure valve problem.