Thread: Surging/missing GTP

Ok, a little backstory.

1997 Grand Prix GTP 157,000 miles. Rebuilt the entire engine about 1000 miles ago.

Bottom end: Stock bore block honed/hottanked/linebored,ARP mainstuds, stock crank polished, stock L67 rods reconditioned w/arp wavelock bolts, stock pistons w/new rings, new cam/rod/main bearings, ZZ XP camshaft, double roller chain, stock lifters.

Heads, ported L67 heads w/oversized SSI valves and 130# springs. Blower rebuilt and ported, lower intake port matched to gasket/heads. Slight porting on TB. SSAC headers, no cat, egr delete, Autolight 104 copper plugs, ZZP's Taylor wires w/MSD ends.

Injectors were cleaned and flow balanced. Tuned by my friend Brian.

I think thats it. Alright, car runs great, starts every time, I drive it back and forth to work (104 mile round trip) for two weeks to break the motor in, driving like an ol' lady. Changed over to synthetic oil after the first week (about 500 miles).

One morning (4:30 am) I'm on my way to work, nice weather, not to hot, car is running fine, I decide to get on it in second gear. I run through second, shifts at 6000 rpm and..... it feels funny, like something just let go. Big decrease in power and missing badly. I barely make it the last 4 miles to work.

I'm thinking bad coil at first (felt like when my MSD coils went bad, I have GM coils now) so I order up a coil from a local auto parts store hoping I can just swap it at work and drive it home. Well, all the coils appear to be firing HOT so I leave it at work and return the next day with my truck and trailer and take it home.

Next I'm thinking ICM, but the one on the car checks good. I even have a spare and threw that on there no difference.

Next I pull the hose to the fuel pressure regulator and smell fuel. I replace that and there is a marginal improvement. The car will now idle but is still surging/missing.

All vacuum lines appear good, but when surging/idling i'm getting a reading of 0-10 lbs of vacuum. Motor sounds OK, no unusual mechanical noise. Plugs are black, but no smoke out of the exhaust. It does smell fat. No check engine light. Pulled the plug for the MAF and the car just dies so I'm assuming that is OK.

So I can't get a laptop hooked up to it just yet to help me trouble shoot this thing and I don't want to just throw parts at it so I'm wondering what to do next troubleshooting wise? Before I start taking it back apart anyhow. I have an intercooler to install but no sense doing that until I get it straigtened out.

This is'nt my DD, but I'd like it to be.

Thanks, John

Sounds like you have a really bad vacuum leak.

I know, I going to get some gumout and spray around the motor to see if I can pinpoint it. All the hoses and connections look good, pretty frustrating.

I put the aluminum LIM gaskets on when I rebuilt, are there any problems with those "blowing out" or leaking?

did you rtv the corners?

Yup.

Thats the worst, going over all the little things you did, and then wondering if it was enough. I've assembled a few motors in the past, this was probably the first in over ten years though. I tried to be very meticulous about everything, had it all laid out and organized and took my time. My buddy Brian has assembled a few of these 3800's and he and I took our time and did'nt drink any beer until we were done lol.

I'm off to O'rielly's to get some gumout lol. I'll be back to see if anyone has any ideas. Thanks!

Post pics of the engine...and all the vac line areas, maybe you're missing something obvious.

Also, missing could also be coming from those crappy Taylor/ZZP wires too.

Did it throw any codes?

Originally Posted by matt5112

Was every plug pulled?

Were they cleaned before being reinstalled?

Na, just pulled the "easy" ones. Did'nt clean em' either. I've got some Brakecleaner now and I'll pull em' all and douch em good. I'm also gonna check resistance on my "crappy" Taylor/MSD wires lol.

Probably gonna hit her hard tomarrow as I've got a lot going on today, installing hardwood floors in my house lol and need to get it done before I can "play" in the garage.

Just trying to get some ideas/suggestions together here so I don't just stand there looking at it scratching my head.

Spray carb cleaner, get a way to scan it.

Check the LTFT's and if they are pegged at +16.4, then you in fact have a vac leak.

I said crappy ZZP/Taylor wires because they are known for their issues...

Best wires for these cars are either lifetime warranty replacement stock ones, MSD's, or PRJ's.

Long Term Fuel Trims.

If they are fluxuating...then you're golden...at WOT you want them evened out as close to 0 as possible. But at a closed loop idle, after about 30 seconds...if pegged at +16.4...you have a vacuum leak.

Was it tuned for the ported TB?

If not, then it could be running lean enough to toss up a crazy vac leak...but when mine did that I also got a P0171 code, which is bank one lean...once I had it tuned for the ported TB, it went away.