Thread: Running Rich 04 GTP

My 04 GTP comp G has been running very rich recently to the point I stopped driving it so I wouldn't mess up the Cat. I don't know if they are related or if it is coincidence but the throttle position sensor went south at about the same time causing a lower power warning. I replaced the pedal assembly and the error codes are gone but ever since I've been extremely rich.

I needed to replace the lower intake due to a slow coolant leak so while I was doing that I replaced the upper O2, MAP, BAR, Injectors and MAF along with new spark plugs/wires since most of that needed to come out anyway and most of them were original. But none of those were the cause. The only mods are a CAI, front power log and a ZZP 3" downpipe that have been on the car for years.

STFT and LTFT are in the -20s most of the time. There doesn't seem to be an exhaust leak anywhere. I tried finding what the fuel pressure should be for the 04 with the return less system but I have found a lot of conflicting numbers during searches from 42-50psi? So if someone has a shop manual with those numbers I'd appreciate it. - Thanks

Thanks for the advise. It's all AC Delco sensors with NGK plugs on a stock tune. It was running rich before and after the sensors were replaced so I don't think it's related to one of the sensors. I didn't notice any exhaust leaks but I'm going to pull the front P log and inspect it for any cracks since those were a bit notorious for cracking at the welds.

Unplug each fuel injector and write down what the fuel trims are after idling for 5 min after unplugging each injector. Only thing that can cause our cars to run rich are bad maf or bad injector. Only other issue I can think of could be a bad 02 that isn't completely dead but it's reading improperly.. a simple check for the o2 would be to cause a rich or lean condition and see if the o2 responds to it . Pull the vac line off the brake booster and see if the trims drop. If they do then you can most likely trust the o2.. I can't hear the motor run so it's hard to diagnose but only other possiblity I can think of is a cyl not firing.. but that would most likely give a misfire code and you didn't mention one so if it's running rich without a misfire code then it would have to be a bad maf, bad injector, or bad o2.. and if your not using acdelco parts I wouldn't trust it... I would start with the maf and if it's not a acdelco maf then replace it just for that reason.. after market maf and o2 sensors do not work well on our cars.. stick with acdelco parts or you will end up wishing you did