New 05' GTP some WOT problems

[J57ltr]

So I purchased an 05' GTP with 136K miles on it. I noticed someone had at least put Flomasters and a 3.4" pulley on it. The factory aribox was loose. When I went to test drive it it drove fine at normal speeds, but knowing it probably needed plugs and wires I got on it and it spit and sputtered and threw a code (multiple cyl misfire), I used this and some other items to pick it up cheap.

I got it home and replaced the plugs and wires and the car seemed to respond, I didn't really get on it hard. Today I added an intake and took it for a spin. The car ran hard and then a few times it seemed to fall on its face. I ran really hard down the feeder and let off and hit it again and it started to miss, like it was loading up with fuel and fouling the plugs. It took several seconds and a downshift to get it to run again. The car feels like my old Supercoupe would get running too cold a plug or a stuck regulator raising the fuel pressure real high.

I checked the fuel pressure and it was 65psi at idle. Couldn't really rev it since its DBW.. Shutting off the engine only dropped pressure to 60#. This system seems like a return less system so I imagine the fuel pump is controlled variable by PWM.

I should also note it acted the same when the factor od was installed.

Thanks,

Jeff

[Fivefingerdeathpunch]

Likely too much knock, computer retards tons of timing to try and not blow the motor up. Remove 3.4 pulley is one of the first steps.

And did you replace the plugs with Iridiums or coppers?

[Uno99]

Yikers!! Are you sure its a 3.4 if so its going to be knocking like hell. To run a 3.4 on a gen v car you need alot more than some mufflers. I would be surprised if you got yourself some chipped pistons from all the detonation. Dont go into boost anymore until you can either get the supporting mods for the 3.4 or get a stock pulley back on it.

[02NavyBlue]

Thought you said you were gonna take it easy until you get a safer supercharger pulley?? Lol

[J57ltr]

Lol, I was taking it easy. The exhaust is 2 1/2" from the rear manifold back to the stock Y. I hear no detonation, I understand that it could be happening, but it can't be pulling so much that it feels like the engine is running out of gas. The old plugs were Very rich.

[J57ltr]

Just to put it into perspective what should I get for the stock size?

[Fivefingerdeathpunch]

3.8, same size as the motor.

Those are the stock sizes for any supercharged grand prix.

[Uno99]

Do you have anything to scan it? Would like to see how much knock you may be getting. What temp/kind of plugs are you running?

[J57ltr]

Given my current setup what side pulley do you think I can safely run.

Here's pics of the exhaust

http://www.grandprixforums.net/threa...-New-GTP-owner

[Fivefingerdeathpunch]

3.8 is your only option. Not enough exhaust flow.

That Gen V supercharger is better than the previous gen 3 on 95-03 model 3800's, it makes more boost and is more efficient overall.

Figure if one was modding their car, a 3.4 on a Gen 3 is like a 3.6 on a Gen V, so with that 3.4 on yours thats like having a 3.2 on a Gen 3. I bet it's trying build like 10-12 psi currently compaired to the 8ish stock, and it have a hard enough time as it is to get all that air/exhaust out in stock form.

[J57ltr]

I'm running ACDelco 41-902's

I only have a standard scanner for codes and IM ready stuff and clearing codes.

Looking into one of them Bluetooth things LM-327 or something.

[Fivefingerdeathpunch]

Not to shame you more, but when I interneted those plugs they came up as platinums.

It's not a good idea to run platinums on a 3800. We have a waste spark ignition systems and they cannot handle it. WSI will fire the coil for 2 cylinders on every compression stroke, be it intake or exhaust for whatever cylinder and plats break down quickly and dont hold up.

Some may last a few thousand miles or they last 10 minutes before they die.

[J57ltr]

Thanks for the explanation on boost vs pulley vs ac gen.

It was very much the same on the supercoupes but 89-93 had a smaller pulley than 94-95 but they both ran 13psi stock. Granted we had aluminum heads and intercooler

Jeff

[chrsmi1]

Get an ELM-327 off of amazon or ebay or wherever and then download the torque app and scan for knock retard.
3.4 with no flow mods, I bet 10 degrees of knock.

And if you keep going WOT, a blown engine.

[J57ltr]

I'm having a real hard time believing that. We had waste spark systems in the supercoupe as well and you could run Double Platinums Iridiums were just coming out we easily got 40k of of them with hard use. Now Bosch single Platnums were luckly to last 5k.

There can't be that much difference between these engines can there?

[Fivefingerdeathpunch]

Ford and GM is the biggest difference.

It's a known thing around these cars, platinums are just not something you can run and have any trust in them.

[chrsmi1]

Ford and GM is the biggest difference.

It's a known thing around these cars, platinums are just not something you can run and have any trust in them.

This guy is a 1000% right. I've owned two GP's, both supercharged. Took my first to a shop about 10 years ago, they put platinums in it. Ran like crap.
Coppers are the best for our engines. Bite the bullet and change them twice a year. It's 20 bucks and if you're real slow, an hour.

[J57ltr]

Well my list was going to be a power log, I'll do my own exhaust from cat back. ZZP 3" downpipe and I'll get a 3.8 for now. And the LM-327.

[Fivefingerdeathpunch]

Copper is the best if you wish to mod.

Iridium is the best if you only want to replace them every 75-100k miles.

Even the brand new corvettes and caddy ctsv's all run Iridiums plugs from the factory, just a colder plug at that. Also an option for us, they are roughly 2-3 steps cooler but research is key there. They just cost more in the end.

[J57ltr]

Wow that's an eye opener. We only ran coppers at the track, because that's about as long as they would last. I'll pick up some coppers tomorrow, assuming I go back to the 3.8" what heat range is recomended.

Wow, it's like all the information i acquired tuning EECIV using EEC Tuner is null and void. Hell none of how to launch a IRS 4200# with a manual trans car at a track is worthless now.