2004 Pontiac Grand Prix gas mileage problem..

[Sporkhead]

My brother owns an '04 Grand Prix GT (I think?)
it's a 4 door, and has duel exhaust,
either way, it usually gets fantastic mileage, but now it's gotten so bad it takes half a tank of gas to travel 37 miles to work...
anyone have any idea what it could be?

[Ralph]

I may be wrong but I can't see the engine running taking that much fuel. My guess is look at the fuel lines for a leak or a crack in the tank

[karnoff]

that, or possibly an o2 sensor?

[Sporkhead]

I was thinking a leak too, but we let it sit in the driveway for a day, and there was no sign of any leaking under the car, or anywhere..

I was thinking o2 sensor aswell, but I'm not totally sure..

[Brad97GS]

Have you smelled under the hood (or around the car at all) for gas? It could be leaking while running, such as at the quick connect points in the engine bay. That can be VERY dangerous!

Seems to me that if it were really going through that much gas, you'd be seeing black smoke or even raw gasoline coming out the tailpipe when running...