Terrible mileage 01 gt [Archive] - GrandAmGT.com Forum


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01-31-2013, 03:28 PM
Anyone have ideas why my mileage is so terrible. This is all town driving and maybe 2 total hours of idle/warm up time. Yes I know all town driving in winter will be a little worse mileage, but I have an 8th tank left and am at 139 miles on the tank. Anyone have ideas. Nothing is plugged and everything is clean. New intake gaskets, plugs, wires, t stat etc when replaced.

01-31-2013, 05:55 PM
did it get good mileage since u changed intake gaskets?
i got the same problem been thru all kinds of possibilities changed a bunch of stuff
everyone as said check air pressure in tires, make sure air filter is clean, injectors working, what kind of gas u running, o2 sensors, fuel pressure, brakes hangin up, wheel bearings free
all things i was advised to check out on my gas hog, hope you find the problem

01-31-2013, 06:45 PM
how many miles on the car? original catalytic converter?

maybe you just got some bad gas

02-02-2013, 12:16 PM
I only get about 15 mpg city right now but that is because I need to replace my upstream O2 sensor. It is making my car run really rich. Bad for fuel economy, but great on power.... subjective opinion of course.

sugar ray
02-05-2013, 11:23 PM
My 02GA did this once. absolutely horrible mileage overnight. Turned out to be a plugged Cat for me. However, I could feel the problem because I had a serious lack of power. Your problem doesn't sound that obvious. I would lean towards a bad
02 sensor. Even a small chance of a small exhaust leak causing back pressure.

02-06-2013, 08:15 PM
Even a small chance of a small exhaust leak causing back pressure.

Ray is technically right that exhaust leaks can cause over rich conditions, but not as a result of backpressure (at least not directly); resonance in the exhaust system can pull fresh air back into the exhaust through a leak, causing false elevated O2 readings which in turn lead to enrichment in closed loop. However, if an exhaust leak is present and is related to a low MPG problem on a 3400, I would argue the more likely cause would still lie with the cat, as a *severely* restricted cat can overheat the exhaust parts enough to warp the manifolds (they'll typically try to 'curl up' at the ends) and pop the bolt heads off, leading to a leak. A P0420 is almost invariably set in this case.

I suspect, however, that OP has not checked enough of the more likely sources yet to be looking at exhaust leaks and cat problems.

03GT SilverGun
02-07-2013, 06:44 AM
Hey man I hope you find the problem! As of about a month ago I've been having the same problem!

Usually I get about 250 miles out of an entire tank and its been getting worse. Last time I filled up I think I only got about 200 miles out of the tank before I had to fill up. And now currently I'm at I think 150 miles and I'm already below 1/4 tank. I haven't noticed and loss of power or anything unusual.

02-09-2013, 01:09 PM
yeah deff no loss of power just terrible mileage, last tank i filled up at around 140 miles honestly.......

02-09-2013, 09:53 PM
I am experiencing the same problem the mileage... got 158 out of the last tank. Thought it was just from letting it warm up. Time to investigate the problem. The o2 sensor would throw a code right?

02-24-2013, 12:56 PM
anybody figure anything out on poor fuel mileage

03-03-2013, 08:58 PM
I am having the same problem. My fuel pump was just replaced and since then i have been getting terrible mileage.