Misfire

1ERALBRIGHT

MEMBER
2003 PONTIAC MONTANA
3.4L
6 CYL
2WD
AUTOMATIC
193,000 MILES

Amateur mechanic (myself) replaced head gaskets on this engine after coolant had leaked into cylinder and burned. Repair went by the book. However, cylinder now one misfires and spark plug looks wet (clear) and sooty. All cylinders all have good and equal compression (145 p.S.I), new spark plugs and wires were installed, coil packs register equal ohms, intake manifold was removed and installed three times carefully, cleaned and tightened to spec, new gaskets installed. Misfires still in cylinder one. I disassembled the fuel rail and injectors, cleaning each one forward and back with a twelve volt battery and brake cleaner. Reinstalled injectors on rail in a different order before replacing in van. No change. No visible exhaust burning. Vacuum leak? Next steps? Possible solution?

7 Replies

SATURNTECH9

MECHANIC
30,869 POSTS

Have you swapped the number one coil with a different cylinder to see if the miss fire moves?

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Monday, May 8th, 2017 AT 11:03 AM

STEVE W.

MECHANIC
13,473 POSTS

Check the wire as well, have seen ones that were bad out of the box more than once. Same with plugs.

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Tuesday, May 9th, 2017 AT 9:36 AM

SATURNTECH9

MECHANIC
30,869 POSTS

I see each coil has two cylinders make sure the one that misfired has spark on that coil post.I have seen coils ohm out good and be bad

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Tuesday, May 9th, 2017 AT 10:10 AM

1ERALBRIGHT

MEMBER
16 POSTS

Thanks a heap for the brilliant tips. I was beginning to think that the new parts may have been compromised, and should have gone back and tested the coil, wires and plugs after assuming they would function out of the box. Cylinder 1 was always the wet one, so that would seem to narrow the culprits down to the individual coil or wire which were not switched in the process (the plugs got moved around). My apprehension was that it would be a cracked piston or ring spitting fresh oil on the plug, but the exhaust was perfectly clear so that would indicate a lack of spark and combustion while running.

However, given my schedule and time constraints I had to throw in the towel on the family van and have the guys at the shop figure out what I missed. See what they find.

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Tuesday, May 9th, 2017 AT 11:29 AM

SATURNTECH9