Hey all, new 2002 GTP owner here (sedan). Picked it up for a song at a local dealership. 150,000 miles so it's certainly no spring chicken, but I am also well aware that the 3800's are built like tanks and if taken care of (clean carfax and numerous service records) that this car should continue to last a long time. I'm not really serious about modding the car at this point, but it's something I'm keeping my eye on for the future. There definitely seem to be some very knowledgable people here and was hoping I could get help with a few questions.
The car is showing a service engine soon light. It was on when I purchased the car, and the mechanic I took it to at the time told me it was setting a catalytic converter code, but that often the rear O2 sensor was the culprit in this case and would set a false code. I replaced the O2 sensor, and the light went off for a day or so but then came back on. He told me it might do that. Is this normal, could the other O2 sensor also be bad, and is it possible the cat itself is bad? Any way to check?
Second question is probably stupid, but the boost gauge (stock) never seems to show activity unless I really get on the gas. If I go WOT I'm pretty sure it hits full boost, but under normal driving conditions and even moderate to heavy throttle it doesn't seem to show any activity at all, or one bar at most. Is this normal, or is the gauge being strange? I don't see how it's possible for the Supercharger to not be properly boosting except under WOT, so any input would be great.
Final question is gas mileage. I understand this car's no civic, but I seem to be operating in the 15 mpg range which is pretty awful. I expect 20 or so in the city and 25 on the highway at least, and I don't think I'm sniffing that. I know O2 sensors can cause mileage problems, and new plugs/wires are next on my list of things to do for the car along with an oil change, but is there anything I could be missing? I don't drive with my foot on the floor constantly so I've ruled out driving habit as the problem here.
Any help would be appreciated. I'm not a wrench turner but I'm willing to start taking baby steps in that direction with this car. My fiance and I love it!
BTW Mechanic told me that the Cat stayed warm on the car for a long time after he started working on it, and that it sounded pretty solid, both warning signs that the cat could in fact be bad. I'll probably just put a new cat on it and the upstream O2 sensor for peace of mind as O2 sensors are notoriously fickle and he said he'd cut me a deal on the labor to do both.
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