i replaced my lim gaskets and the 2 coolant elbows about 2 days ago. everything went pretty smooth, got everything put back together. but now i have a problem. its not leaking antifreeze anymore, but there is a misfire condition. there is also a weird noise when you first start it up. i got the ses light scanned. came back with codes p0420, and p0300. this happened right after the gaskets were replaced.

we had the ignition control module checked along with all 3 coil packs, they all checked fine.

the reason i think its cylinder 2 and 4: with the car running we pulled each wire from the coil packs. there was a noticeable misfire on every coil except 2 and 4. were checking to see if the fuel injectors are firing today with a noid light. now that should tell us if they are firing, but that wouldnt necessarily tell us if they are bad. we haven't looked at the plugs yet either. any suggestions on what else we should check?

Any chance the spark plug wires for 2 & 4 got switched?
If not I'd change the plugs. If coolant was getting in the cylinders that'* very hard on the spark plugs.

we traced the wires down about 5 times, they are all connected to their respective pack/cylinder. i will have a look at the plugs sometime today. if they need to be replaced, would there be any drawback to using those bosch platinum plugs that dont have to be gapped?

We don't recommend using Bosch plugs. Could the fuel injector wires for 2 & 4 be mixed up?

well, the wire for injector 2 wont reach to injector 4, so i dont believe they are mixed up, but its worth checking out.

what plugs would you recommend?

I like the plain old copper NGK'* or AC Delco'*.

whats the possibility that after changing the LIM gasket, it'* now out of time? i have ordered the FSM but it has not arrived yet, would there be an easy way, or possibly an article to check it out?

suggestions??

i was just thinking of something. if it was out of time, would the motor even start? reason i ask is it used to start and misfire pretty bad, but now its not even starting.

Is the noise at start-up a shriek/squeal?
Also, I second the motion to get rid of the Bosch plugs. I have only heard of 2-3 good experiences pairing Bosch plugs with the GM 3800 engines out of probably close to 100 bad experiences. Find some standard copper Autolite 605'* or if you insist on premium go to Iridium. I have tried to maintain faith in Platinum'* in the supercharged 3800'*, but it'* always come back to bite me.

Two other possibilities are the #2 and #4 wires were damaged during the removal-reinstallation of them, or the coils are shot.
Another option would be to check to see that all points of plug wire connections are connected all the way -it'* been done before and I'm guilty myself, so it'* not just a rookie problem.