• The site migration is complete! Hopefully everything transferred properly from the multiple decades old software we were using before. If you notice any issues please let me know, thanks! Also, I'm still working on things like chatbox, etc so hopefully those will be working in the next week or two.

GTP stutters.. struggling to accelerate

97AutoXVette

97AutoXVette

New member
Good afternoon. my 2002 GTP sedan started struggling to accelerate last week. doesn't have to be in boost. The engine stutters and shakes a bit when I try to accelerate anything over I'd say 15% throttle or so. Idles fine. No CELs, no other issues. What I have done to try and diagnose:

Brand new this week:
AL606 iridium plugs
ZZP 10.5mm wires
ignition coils
ICM

Catless downpipe installed recently as well as PLOG. stock supercharger pulley. EGR delete. Stock injectors/fuel system.

I was almost sure this was going to be an ignition problem, as it has the classic plug-wire/coil stuttering issue, but it's not the case. The only other thing I can think of is a clogged injector or something fuel related??

Open to recommendations on next steps to trouble shoot. I have searched through everything I can find on this forum and others related to this issue and most of them pointed to ICM/coil issues or clogged CATs which fixed their problems. Unfortunately I am still on the search for root cause. Thx
 


I'd try some stock wires and maybe watch misfire by cylinder with a scanner.

It may not be tossing a check engine light but it can still be misfiring.
 
the old wires did work fine, but when I went to do the tune-up on it, one of the wires pulled right out of the boot, so I bought new ones. What is the likely-hood that these new 10.5mm ZZP wires are causing it? any recommendations other than the AL606s?

Thx for the quick replies gents

edit: I do have HP-Tuners Pro as well so I can try and so some scans later today to watch for misfires
 


iirc they used to, but i think they fixed that issue. im not a fan of zzp stuff in general. i got nothing they sell on my car. lol
 
Ha.. yeah, I really like how they're downpipes and PLOGs fit up, but this would not be the first time I have had an ignition-related issue AFTER I have installed one of their ignition components.

Probably going to pick up some stock replacement plug wires at Autozone later today.
 
Have you done a compression check yet? I had a similar condition that ran great when cold but miss fired when warmed up under a load and it ended up being cracked heads.

Sent from my SM-G900R4 using Tapatalk
 
I have not done a compression check. But I would assume if I have a cracked head I would see the oil and coolant mixing? Fluids are currently spotless
 


Just replaced the new ZZP 10.5mm wires with some new AC-Delco 7mm wires from Autozone. still having the exact same issue. Any chance the Autolight XP606 iridium plugs could be an issue? I have not changed the gap. They are gapped as they came right from the package.
 
Well..... found the issue.. After scanning with HP-Tuners and not seeing anything, I decided it was time to pull the plugs to see how they looked, and try to find evidence of any potentially not firing. When I got to cylinder 6 and removed the plug, here is what I found:



I specifically remember when I bought the set of 6 last week, the gentlemen at autozone dropped one of the individual plug boxes on his way to the counter. I almost guarantee it was the same plug from cyl. #6, and he prob put a hairline crack in it.

Good news: replaced the plug, problem fixed, car runs great.

Lesson learned (and I should already know this...): do not throw parts at it (new ICM, coils, and 2nd set of plug wires) until you've investigated all most likely root causes first. Cost me an extra $248 which could have been avoided had I have just pulled the plugs the first day I noticed the misfire.
 
You must log in or register to reply here.
Back
Top