Thread: HELP! Sputter Under Boost (feels like missfire)

Okay so my car did this at high rpm's rarely,
now it does this everytime I am in boost.
I've been trying to find the problem and this is all the info I can offer about the ignition/ fuel system


I have a 97 GTP. It starts up just fine
It has a new racetronix fuel pump and filter
New fuel rails
New 65# injectors,
New autolite 103 spark plugs gapped
Checked out the coil packs and they seem fine
New wires with no cracks
Checked for vac leaks and there seem to be none.
(-20 lbs of vac at idle)
I'm stomped
0.0 KR
No misfires show up on the aeroforce gage???

The car loses A LOT of power and sputters ( feels like misfires) when I accelerate hard or go into boost.

Anyone run into this problem or have any suggestions? Please help a brother out.

Pull the plugs boss...check em. Also any CEL's?

Start with the plugs...depending on age, you might be blowing the spark out since they could be worn. Recheck the gaps on them, and make sure they are wearing properly.

Originally Posted by OrangeL67

I have a 97 GTP.

Doh!!!


A sputtering / loss of power could feel like it is engine related when it is actually transmission related, any tranny problems lately???

I was going to bring up trany too. Maybe tcc related.

Maybe a clogged cat?

Thanks for all the suggestions.

The plugs are new (changed them yeaterday trying to hunt down the problem) They are autolite 103's gapped at 52

The trans is a TEP built less than a year ago

And no CEL light pops up!!

Car starts & rides perfect when I'm out of boost. The problem only occurs when I'm accelerating at about 50% throttle or more. (once I get into boost)

And also, I do not have a catalytic converter

& I'm running Mobil 1 with about 2k miles on the oil

Thanks for all the help guys, but I need more suggestions

Have you hooked a scan tool upto your car? Your dash bulb could be burnt out. I'd want to hook one up if you haven't just to make sure there isn't any CEL's.

it may be related to your tune.

Damn. Just cleaned the Maf. Still have the same problem. It looks like my bypass is doing some wierd stuff when I rev it. It likes to bounce open and closed? I can't figure this crap out

Video of the bypass? It should be open (up position) at idle and closed (down position) under boost or with the car off.

Is any black smoke coming out? I had the same problem but i had black smoke, i disconnected my MAF and punched it a few times and the problem was gone.

Originally Posted by DanGTP

Video of the bypass? It should be open (up position) at idle and closed (down position) under boost or with the car off.

The BBV bounces when the car coughs. However, it does not do this much in neutural or park, so it's hard to get a vid. Usually the car hesitates while I'm in drive and get on it down the road

Originally Posted by batman1988

Is any black smoke coming out? I had the same problem but i had black smoke, i disconnected my MAF and punched it a few times and the problem was gone.

No black smoke. The car literally drives perfect until I get it into boost. Thats when it studders like I'm revving out off the limiter, but the rpms will slowly bounce thier way up through the powerband.

Disconnect your MAF and go for a drive, build up boost a few times and see if it goes away. If that is not it, i would check for a vac leak. I could be wrong.

That sounds just like what happened with mine when a coil pack went bad...
It didnt blink and CELs like it should with a misfire...

Go out tonight when it's dark, pop the hood, and rev the engine, and see if there are any sparks...


its just a thought, and pretty easy to check too...Once i changed the coils out, the stuttering/misfire went away

Didn't think about the knock sensors. Is there a diagnostics test for them? Or, does one just change them and hope it solves the problem?

are the values static?

my car is doing the exact same thing but i think i know why on mine check all out connectors especially the one in the back mine is broken and not sitting in all the way and i keep coming up with p1361