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Old 05-25-2010, 04:07 PM
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GM 3.4L hanging valve?

2003 grand am 3400 engine. confusing problem with it.

plp are from out of state stranded here because the car was going down the highway and all of a sudden it started missing on cylinder 5 and flashing CEL and all that stuff. only 100k miles on it.

tried new coil pack and module and wire and plug and injector on that cylinder and still dead missing on that cylinder, it is getting fuel and spark both.

on exhaust tailpipe it is sucking pretty good up the exhaust constant speed at idle. and kinda hear a pop suck kind of sound in the tail pipe

im afraid exhaust valve is hanging up at idle speed.

compression shows 120psi with module unplugged and just a quick crank.

what do you think?

we are lost.

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Old 05-25-2010, 05:40 PM's Avatar
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These engines don't have valvetrain problems in general. They do have head gasket and intake problems every day. Especially on the end cylinders.

A miss can be attributed to either.
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Old 05-25-2010, 05:57 PM
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true enough. youre right these engines dont have valvetrain problems in general usually.,
it can cause the miss, with a burnt HG, even though you wouldnt think it., im not really sure how it does it but it just does hmm.

and since it did mess up and need a gallon or more water the other day,, (apparently it was overheating)

and it is actually getting pretty overly warm today too... wont cool off and run normal temp.

must be head gasket yeah...

in which ive had to do alot of on these and the 3.1 recently again


although i did forget to check the coolant tank for any large bubbles coming up it while its running hmmm.... thats usually what you see on blown HG issues... but also usually antifreeze exhaust or white smoke too,,, in which this car has neither one of happening

the only other thing i can think of that i forgot to post is that one time i fired it up today it hammered knocked for a few seconds and then stopped doing it, but this was in the front most valve cover,
the 2,4, and 6 cylinder side.

and not the side with #5(the rear most head)

so hmmm..

this just happens to be the first gm FWD v6 that has had a cylinder miss that we couldnt solve by replacing either the injector or ignition parts.

so hmm,..

can a burnt HG cause the sucking up the tailpipe issue? if so how does it? and why is the compression reading perfect at 120 then?

intake lower manifolds gaskets done already.

this thread taught me alot of good new info. apparently 120 is not normal for these 3.4 engines??


checked compression on cylinder number 2 and got 85 lbs

something is wrong here with this engine yeah.......

pulling both heads tomorrow...

i feel sorry for this young couple stuck here from phoenix now in crappy *** central il here now until we get this resolved for them the next couple days hopefully.

i feel for them i been in this situation when i was stuck out of state with a toasted th200c trans in a 79 caprice i had in 2000 and had to have repaired there so i could get back to here,,,,

these damn 3.1 and 3.4 engines love to puke head gaskets and LIM gaskets too.. so common.,,, also timing cover gaskets..... been doing so many more of them recently than ever before wow..... but the symptoms arent quite the usual same this time,, for a bad gasket like this.... hmmm

got a 2003 impala ss with 3400 in it and super low miles its clean and purrs we robbed the module and coils from it to try out on this grand am, didnt change nothin though, of course. also swapped the MAF from it, also no change at all.


Last edited by fast68; 05-26-2010 at 01:14 AM.
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