misfire help
misfire help The car is a 2005 GTO with a built 402 and it has developed a mis on cylinder number 4 only. Its worse from 1500 to 2200RPMS, and cannot be noticed after that. I pulled the plug on it the other day and it was black. After moving some things around, it still had the same problem. There does seem to be a bit of oil in that intake port as well as around the gasket on the manifold. I have not noticed any smoke either.
Heres what ive done so far...
changed the plug
swapped coil and wire
swapped coil brackets
put extra thread sealant on intake rocker bolt
checked the valve springs
did a compression test
Compression test was good, so that would suggest the piston and rings are good. I dont have an air compressor at home or i would have done a leakdown test too. lack of smoke suggests the head gasket is probably intact too.
Im kind of at a "where should I go now" moment. I was thinking to swap the injector, but to me the oil suggests that wont work. None of the other cylinders have as much oil in the runner as number 4 does (which is not a lot)
edit: A little more info...
Swapped the injectors a little while ago, same thing happening
tested the spark and it looked the same as a few other cylinders
I check the wiring to the injector and it was getting batter voltage and the other side was not a short to ground. I do no have any noid lights though.
I tried a running compression test, but my gauge did not like that (and i did not use the schraeder valve)
Heres what ive done so far...
changed the plug
swapped coil and wire
swapped coil brackets
put extra thread sealant on intake rocker bolt
checked the valve springs
did a compression test
Compression test was good, so that would suggest the piston and rings are good. I dont have an air compressor at home or i would have done a leakdown test too. lack of smoke suggests the head gasket is probably intact too.
Im kind of at a "where should I go now" moment. I was thinking to swap the injector, but to me the oil suggests that wont work. None of the other cylinders have as much oil in the runner as number 4 does (which is not a lot)
edit: A little more info...
Swapped the injectors a little while ago, same thing happening
tested the spark and it looked the same as a few other cylinders
I check the wiring to the injector and it was getting batter voltage and the other side was not a short to ground. I do no have any noid lights though.
I tried a running compression test, but my gauge did not like that (and i did not use the schraeder valve)
Last edited by 05gto60; Apr 25, 2011 at 10:19 AM.
actually, that happened to me last year too. lol. that was my first guess too. i do not see a broke spring, unless the inner spring is broke. I was thinking of removing the springs this week just to triple check.
hmm also did you check the plugs on the opposite side when you swapped coils?
Might just be your coil harness, Pace sells those at like 60 bux a piece.
sorry just brain storming. I had one go bad before, if you have had yours on and off lots of times like I had. LOL
Might just be your coil harness, Pace sells those at like 60 bux a piece.
sorry just brain storming. I had one go bad before, if you have had yours on and off lots of times like I had. LOL
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Verdad Gallardo Here is a question for someone, would a burnt exhaust valve show up on a compression test? my guess would be yes.
I need to borrow an air compressor from my friend and just leak test this thing.
I need to borrow an air compressor from my friend and just leak test this thing.
I pulled the valve springs off today and they look great still. I also checked the control wire for the coil on number 4 and it was fine.
Im trying to narrow down the list of posibilities though...
-Bad PCM (kinda hard to test for in Italy, even hard to replace with the need for a TECH2)
-worn cam: wouldnt show on compression test with a slow moving motor. id have to look at valve movement with a dial indicator.
-burnt valve: kinda doubt, but possible. this should have shown up on the compression test.
The wiring is good, so the only issue with spark and fuel would be in the PCM. it wouldnt suprise me if something in the computer was messed up though
Im trying to narrow down the list of posibilities though...
-Bad PCM (kinda hard to test for in Italy, even hard to replace with the need for a TECH2)
-worn cam: wouldnt show on compression test with a slow moving motor. id have to look at valve movement with a dial indicator.
-burnt valve: kinda doubt, but possible. this should have shown up on the compression test.
The wiring is good, so the only issue with spark and fuel would be in the PCM. it wouldnt suprise me if something in the computer was messed up though
