misfire at wot above 4k rpm... not always..

[Yaj Yak]

alright so i made some changes to my car bout a week ago... and now... sometimes... when my car gets warm... above 4k rpm- it misfires...

not violent enough to give a code- but enough to feel it, hear it, and notice it...

major changes that may possibly have caused something i made from before are as follows:

replaced m90 case with block off plate... with custom intake manifold

re ran vacuum lines because of this mod

tr6 spark plugs instead of al104s- spark plugs gapped at .04... could this be my problem????? too big or small of a gap?

what or where should i check?

it really seems to only happen once the car is significantly warmed up...

it didnt do it before i changed stuff... but now is.

Click to read more...

 

[Outlaw]

Spark is a good place to look. are you running the stock GM coils or have you upgraded to somthing more powerful? Your most recent mods may have been just enough to put you over the edge where the stockers cant handle it... also, just for shits, put your old plugs back in, that'll be the easiest way to rule out that. I never did plugs on my 3800 but, at least you'll rule it out. good luck nonetheless.

 

[Yaj Yak]

good idea. thanks for that...

i do still have my old plugs so yeah...

and i have seen guys have pretty good luck with stock gm coils on these cars... so i figured what was good for the gooose would be good for the gander...

 

[Outlaw]

no problem man. I'm going off experience with a DSM that I had a misfire problem with and it ended up being the coils could not keep up with the demand and ended up going with a MSD coil over plug setup. fixed that right up. hope your problems are as easilly solved.

 

[Yaj Yak]

its just goofy that it waits for it to be warm to do it

 

[Freebeer187]

Im saying its a spark issue. I had similar problems with my GP. One plug was cracked, but still firing. When the S/C was "activated" (or 50% throttle + to active some nice boost) the motor would stutter. Changed the plug and was back in business.

 

[OffshoreDrilling]

Check plugs and wires KJ. NGKs are notorious for cracking the ceramic insulators. Try tightening the gap down to .037-.035" if your wires are okay and the plugs all look fine as well. With a decent amount of boost it wouldnt surprise me if you are blowing out the spark. I run mine gapped at .037" on a naturally aspirated motor....