My wife's 2000 GP SE (86500 miles/3.1 L V6/no mods) is sucking gas like crazy all of a sudden. It's getting maybe 14 or 15 mpg's. It ususally gets around 22 mpg's. There is also an odd, almost, humming sound coming from the rear of the car by the gas tank.

I had the oil changed Saturday and ran Gumout Fuel System Treatment also. It also had a slight knock before the oil change and the SES light was on. I washed the car and was on my way to AZ to have the code read and I noticed that the light was out. The knock also went away.

Any ideas?

Thanks,
Brick

See if they will scan it anyway. Let them know that the CEL was on and turned off on the way there. It sounds like an injector was hanging and causing a mis-fire code that tripped the light. Keep an eye on mileage and see if maybe the Gumout freed up some varnish/deposits that was hogging up an injector. IF AZ can pull any codes, post them here.

AZ didn't pull any codes. They said that since I had turned off the car after the light went out that it would not hold any codes. Sounded fishy to me, but oh well.

That still doesn't explain why it's getting that bad of gas mileage though, does it? 14 or 15 mpg's are on the highway and city driving is even worse.
Could the Gumout cause problems with the fuel pump? I'm at a loss here, because it has never had gas mileage problems before.

Thanks for the help,
Brick

:banghead: