I just bought into the gp world and now i'm stuck. Don't get me wrong i've always loved this car, but I bought the worst one out there. Heres the story I bought it knowing it needed a fuel pump and transmission for 500. I ended up buying a factory fuel pump because a used one was very little savings, then I pulled the trans... I don't even want to tell you about that, so trans back started runs like crap. Cracked front exhaust manifold and It struggles to rev up. Is it a common problem to crack the manifold? I'm leaning towards a plugged cat, but I want to know if the cracked manifold is a common result of a plugged cat, or if I should just junk the car and stop putting money into it.

cracked manifold? where?

a plugged cat would make the manifolds glow red hot. that might make a potential situation for one cracking with the heating and cooling, but thats pretty bad. start your car up, let it run and open the hood. if those mani's are glowing then you know whats wrong.

if not, maybe you've just got a screwed up manifold. they are pretty cheap. hell, ill sell you mine that isnt on my car anymore if you really need one. either that or its a great time to upgrade.

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98 XGT - 3.2/3.4, s&s, ported m90/TB/LIM, 1.9s, jp dbl; tinted, blacked out, lowered
soon -> e85, meth, and a lot smaller pulley

I can barely get the car to run. Right now it's almost impossible to get it moving and that's with the car on a rack with the wheels off the ground. with no load on the car it can barely get to 60 (by no load i'm talking about wheels in the air off the ground) I'm basically just trying to put a story together to find out why the car runs so horribly since i have no history on it. I'm getting map sensor codes too, is there a map sensor on this vehicle, or is it the mass air flow sensor?

you should find a weekend warrior to rebuild the entire engine for a good price. the car was only 500$.

if your manifold is really cracked, thats probably why it doesnt run. thats like straight off the heads, dont work that way.

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98 XGT - 3.2/3.4, s&s, ported m90/TB/LIM, 1.9s, jp dbl; tinted, blacked out, lowered
soon -> e85, meth, and a lot smaller pulley

I really don't want to go jumping into a engine rebuild till I find out why it's not running correctly. The manifold crack is a hair line crack it's not an actual break the only reason we found it is cuz you could hear the exhaust leak from the front of the engine. I actually removed the engine oil pan cuz it was leaking and it was really clean in there, and visually everything looked good at least from the bottom, if anything I would just pull the heads, but the car isn't showing signs of overheating to be concearned with a blown head gasket at this point.

has the cat been checked? A bad cat will keep the engine from running

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Steve
'97 GTP VS cam, ZZP PCM, and not much else yet

The cat hasn't been checked yet, but when I started it up all kinds of rusted metal shards shot out of the tail pipe, but the car has been sitting for over a year without running so that could just be corrosion. If I floor it in park it won't rev past 2000 rpms

I don't know if a cracked manifold is common or not, but the one on my 97 was cracked. It didn't cause the problems that you explain, but it also wasn't cracked as bad as your in that I couldn't hear any exhaust leak at all. But it did run better when I replaced it. Your best bet is to start with replacing the things that you know are wrong. Start with replacing the front manifold and go from there.

It is very hard to diagnose a car when there is something that is bad. The cracked manifold can cause all kinds of problem if bad enough. And it is pretty bad if you can hear the leak. And if you can hear air coming out, then outside air is going into the exhaust, and messing up the reading of the O2 sensor. So change what you know is bad, the manifold and see what happens.

As for the MAP sensor. Yes, these cars have a MAP sensor. One thing though is that you never said what model of grand prix it is. Is it a SE, GT or GTP?

As for the cat, I wouldn't trust a cat that is over 130k miles or so. Sure some people run them for longer. But they get hot and wear out. If it is possible, I would just remove the entire cat (check local regulations first). If not, get a good high flow cat and a larger downpipe, and get rid of the very restrictive u-bend. All of that can be done considerably cheap.

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1997 GTP - 200k+ miles, PEMs, 3" SS Exhaust w/ Borla Mufflers, 3.4", 180* stat(summer), FWI, 1.84 RR, PT, SLP hood, KYB GR2s, GMPP Handling Kit, etc...

ok, I know this sounds like a no brainer..but have you rechecked the spark plug wire routing?

I wouldnt trust the coil pack numbers...as they are easily switched around.....

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2001 GTP street car- GT45 turbo,Stage 4 Intense turbo cam,FMIC,150 wet, double roller timing chain, Diamond forged coated pistons 8:0:1, Diamond piston rings, cryoed L32 connecting rods, Cryoed crank, Clevite77 main bearings, Clevite77 cam bearings, Clevite77 L32 rod bearings, ARP Everything, Intense/meizere true billet Flexplate, Custom UIM, Intense oil pressure kit, Cometic 4 layer head gaskets, OE-R lifters, Cryoed L67 block, ATI turbo dampner, MUCH MORE, 6 more to choose from ASE Certified