3400 bad miss

[bremen242]

well, my buddy with the 1999 grand am got his heads and head gaskets changed, and now the car warms up.

however, one problem.

the last time we took his car for a drive (when it overheated for the last time), the SES light came on, and it started running REALLY bad.

fast forward-

heads & new head gaskets on, car throws a P300 code -> random/multiple cylinders missing.

put a timing light on each wire, and sure enough, the 4 cylinders on the left & middle were randomly not sparking. however, the front and back cylinders on the far right coil pack where firing fine.

my '94 has a seperate controller for each coil pack, the 99s have one controller for each.

so, did the controller die when the car overheated or did the 2 coil packs overheat?

[imported_germ]

make sure the connection is clean first and if need be, sand down the post on the coil pack with some fine grit sandpaper. rust likes to collect there.

and if you do determine that its the coil packs, i have an extra set i will sell for 30 shipped to the US. they worked fine when removed and have about 65k on them

[bremen242]

so you think the problem is probably somewhere within the coil controller or coils?

[imported_germ]

well, from the way you describe the issue, the only thing it could be is the coil packs, wires, or plugs.

do this to verify....

take that one coil pack that you know is good and swap it over to a known bad sparking coil pack. use your light and check to see if the misfires moved or if they stayed the same.

if they moved, well you have bad coil packs. if it did not move, check your wires and swap them around. if the misfires dont move when the wires are moved around, then check plugs. if it doesnt move then, well, your wiring is messed up somewhere.

[bremen242]

we swapped the coil packs and ICM with one from the junkyard- got the same thing.

it happened with the old and new wires too.

what controls the spark / timing aside from the ICM?

[DEI37]

Crank sensor and ECM. I'd start looking at an ECM, most likely. If you swapped in a different coil and ICM assembly, I would think you've ruled that out as a problem. Time to start digging deeper.

Also, in the overheat, the block COULD have cracked...unsure as to whether or not you'd see coolant in the cylinders from that, but, anything is possible.

[bremen242]

any good way to check the crank sensor?

[imported_germ]

i was having a bad misfire recently as well (last night actually).

it ended up being the injector driver from inside of the computer (PCM) or ECM for you OBD1 guys?

i replaced the PCM and had 0 misfires.

you may want to look at that as well.

[bremen242]

Hmm. I'll have to tell him about that- he has the OBD2. he has a couple cylinder misfiring though.