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Misfire Cylinders 2 & 4

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03GTP

New member
Driving the Grand Prix and upon slowly pulling out of a parking stop I thought I heard some bad knock in the engine bay. Didn't think anything of it and after a hour drive hour via interstate I start noticing a slight misfire at idle. Scan and it turns out #2 & #4 are missing. Spray brake cleaner all around and can't find a leak (still pulling 21"mg at idle in park). Pull the plugs and both insulators are cracked and slipped over the electrodes. Replace the plugs and now I only see the misfire on #2. Had a bunch of parts left over from when I built the car and tried wires, coil, computer under coils, and injectors with no help. What are my next steps? Lifter? As I originally broke #2 & #4 simultaneously, could it be the head gasket between the two cylinders?

Thanks,

Matt
 


Did you loose anything off the plugs? If so might want to get a borescope in those plug holes and check out the piston/cyl walls.
 
The porcelain is still hanging on, thankfully is was not bouncing around in the cylinders. Last night I did a compression check and all 6 cylinders ranged from 177 to 192 psi. #1 was the lowest at 177 psi and the other 5 where between 188-192 psi Cylinders 2 & 4 were right up there with the highest at 190 psi each. My thought was I blew the head gasket between those two cylinders, however I am now not so sure with the good readings. Possible lower intake leak? I believe I am consuming coolant and cannot find an external leak. Possibly coolant is getting sucked into the head and spraying the spark plugs, breaking the insulators?
 
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