2005 supercharged 3.8 grand Prix issues


Asked by Jan 28, 2016 at 12:05 AM about the 2005 Pontiac Grand Prix GTP

Question type: Maintenance & Repair

I have 2005 grand Prix gtp with the SUPERCHARGED 3.8. With 88k miles I replace the
lower intake gasket & scharger gasket cuz of lack of power an codep0300 mult random
missfire . didn't help changer coils even swapped off a buddy's car still nothing. Changed
the cat for bout 2 weeks car ran quite nice went back to doing the same thing. Tue cat
was the mid grade version that Napa offered ran like 375$ I believe part only. What's
going on? Also now cuz of money issues had to continue driving the car I've got lifter
noise. How much difference will I see if I hollow the cat out or put straight pipe in? All
suggestions welcomed

6 Answers


Well did you try the direct fit cat cause Napa has a mid grade like yu said ?


There is a vacuum line in back of the supercharger look at the vacuum line and see if it is collapsed if so the is you problem


I had a reduced power code and it turned out to be the vacuum lines that run from the super charger. Only 20 CAD from gm


The vacuum line is fine. That was the first thing I changed


Yes the cat was a direct fit.I have read on some gp forums that the last ten GPS have issues with aftermarket cats. That the supercharger versions clog up everything except for oem. There's gotta be a cheaper option than the 1000$ gm cat though.


If you want to try a high flow cat I would suggest zzp. http://zzperformance.com/3800/exhaust.html I've been using there's for 50000 kms and no codes yet. It's $130 USD plus shipping.

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