Engine Performance problem
1999 Pontiac Grand Prix 6 cyl Front Wheel Drive Automatic 150000 miles
I have a 1999 grand prix 3.8 that is not supercharged. Im getting 13 mpg with it and I know it should be much higher than that. The car runs great, no missing no hesitation.I changed the O2 sensor before the converter also I changed the air filter and fuel filter. I did a fuel psi test nd with the key on not running I had 48 psi with the engine running it drops to 42 psi. It ahs no codes in the computer, I took to local shop and they said it was running lean then go rich and then lean but stayed to the lean side the most. I can not find any vacum leaks but when I put my ear close to the upper plastic intake manifold I can what sounds like air rushing in its quite loud but I have never listened to one that close before so im not sure if that is normal or not. The other thing I found odd is that if I unplug the MAF sensor I get no codes, so then I unplugged the MAF, TPS, IAT sensors all with the car running and still no codes. The only way I got a trouble code was to pull off a spark plug wire then I got a misfire code. What am I missing or not seeing with my problem?
have the same problem?
Monday, March 9th, 2009 AT 6:37 PM