1st Apr 2009, 15:06
I have a 1995 Grand Prix SE with the 3.1L V6 in good shape that I bought used with 120,000 miles on it.
When I first got the car, it was terrible on gas, driving it easy and really trying to get good mileage still gave me just under 17MPG on average. My previous car had been a 1990 Grand Prix SE also with a 3.1L that I also bought used, and I had had a similar problem with that. Diagnostic codes revealed nothing helpful.
After numerous times in the shop and repeatedly getting it back and being told "it's fixed" and having no change, I finally decided to take a pot-shot-in-the-dark and do it myself. I bought a good used coil pack from the junk yard for $20 and put it in, much to my relief, it fixed it. When I realized the same thing seemed to be going on with the '95 GP I decided to gamble on that one too. My $20 gamble paid off again, the mileage immediately jumped from under 17MPG to over 22MPG when driving normally around town, and not flat and level, this town has lots of hills. On the highway I now get 28+MPG if I'm driving it easy.
What I learned from my experiences is that diagnostic codes apparently DO NOT tell it all. Between wasted gas and too many times in several different repair shops and hearing "it's fixed" and paying the bill only to find that nothing was different, I REALLY wish that I had taken the $20 and the time to do it myself and gambled a lot sooner... TWICE!!! I could have saved myself a lot of money... Oh well, live and learn.
BTW, if you've got a heavy foot on the gas pedal, these cars will suck down the gas pretty fast no matter how good it's running.