Thread: 99 Grand Prix endless problems

So as stated in the title I have a 99 grand prix gtp that seems to have endless problems. I recently invested quite a bit of money into a new cam and smaller pulley with supporting valve train mods. I took it to my local tuner who is reputable and got it tuned. It drove great for 200 miles then I started to get a random misfire in all cylinders. We have just replaced the fuel pump, spark plugs, wires. Since this is a random misfire the coil packs don't seem to be the reason. I was wondering if anyone on here had any ideas. I am leaning to injectors or pcm. If anyones had problems in this area I would greatly appreciate it!!! If I haven't searched hard enough I'm sorry but I just wanted to post what I've done.

Sorry I don't post often. I have had two motors fail due to spun bearings. I've had codes that never seem to go away, and problems that arise right after I fix another. The car is amazing and a complete turd all at once. I'm 19 turning 20 and this is the first car I've ever done performance mods to so yes I'm a noob and theres many things for me to learn. As for the modifications you requested. The ones off the top of my head are as follows. 4 inch intake, 3.4 inch pulley, vs cam, ls7 lifters, ls1 valve springs, the heads were taken to a local shop and the lifters were checked for clearance along with a valve job and new valves, bottom end is stock but ballanced thanks to a spun bearing, 3 inch down pipe, arp head studs, innovate wide band, and thats all I can remember as of now. The motor was rebuilt no more then 15,000 miles or less before the modifications were done which includes the pulley cam head mods and exhaust. So again I have newer injectors (granted I know these could be a problem but I'm looking for other possibilities like the possiblity that he didn't delete a code), brand new fuel pump with less than 600 miles on it, new plugs, wires, and we've swapped coils as I have ex

extras. I was planning on checking fuel pressure and I will call my tuner soon. Any other possibilities?

I had the same issue thought it was coil packs, then cps turned out to be ICM

Does your traction control and/or abs function? If not, that's your problem...

Everything is functioning perfectly other then the misfires, so yes traction and abs are functioning. It seems to only have a real miss under idle but run fine under throttle and there doesn't seem to be any lose of power. I will be checking the MAF as I cleaned my K&N intake during the rebuild, will be double checking the spark plugs to see what they look like, changing the ICM for a spare I have and checking the fuel pressure. I'll keep posting what I'm doing and am looking for any ideas.

Are you sure its missing and its not just the cam? if you havent deleted that code it will throw it with a cam..

See thats where I'm at a lose. I have never done anything like this and I'm not sure what happens when you upgrade things such as a cam. I did a lot of research but obviously theres much more to be learned. I have read that the code will appear when a cam is installed but I was just hoping that someone with the VS cam has had this issue. I truthfully can be 100% certain it's a miss because I'm new to performance mods and still learning on cars in general. It was just odd that it ran fine with no codes for 200 miles but then the codes appeared. I did a fuel pressure check and it was at 47 psi. I'm looking at cleaning the MAF next and checking spark plugs(possibly switching to a different brand), ICM, and possibly the fuel pressure regulator before I go to deleting the codes.

If its running fine then its probably just the code because of the cam if its running fine. Is it P0300? The VS cam is mild and wont throw the code straight away all the time. If you havent already deleted the P0300 code, youll want to. I had a VS on my old car and it would throw the code too but not straight away just like yours.

I felt like it was running great, but my dad feels like it has a miss at idle. It is the VS cam and it is only the P0300 code. It is nice to know that yours threw the code with the VS cam. I am still going to check all that is mentioned above because the car does have 240,000 on it so things do fail. If everything checks out I planned on having my tuner look at the spark and injectors and watch for misses and if there's none I will have him delete it. I just don't want to delete it and still have a problem and blow my motor. I've already done that once and spun a bearing once as well.

So far thats been the only code. Drove it again and was running great no codes and then it popped up. Haven't yet checked on it will soon though.