Sudden drop in MPG
Thread Starter
Racer
Joined: Jun 2007
Posts: 459
Likes: 2
From: Hawaii
Sudden drop in MPG
My 96 LT1 used to get around 19-21 MPG according to the digital display. But now it has dropped to 16.5 and stays there even after i reset it. I use the same fuel and drive the same distance daily. Any ideals on what would cause such a sudden drop in MPG? 
Race Director
Joined: Jan 2005
Posts: 10,641
Likes: 13
From: Slidell Louisiana
Often the digital fuel usage is not accurate however, something changed.
Since you said 96 and LT1 I assume A4 and you said same fuel
that is a significant drop and it could be many things even stupid like dragging brake pad, low tire pressure etc but I believe you'd notice things like that.
So torque converter not locking, howis it running? Is it running rich black exhaust?---- bad O2 sensors, exhaust leaks, ignition problems etc
Did your state shift to a different seasonal fuel blend. I used to get crappy mileage when I was in Kali due to oxygenated fuels.
Basically its a shot in the dark until you add some other details, like road speeds, since TC lock won't give you that big of a mileage hit in low speed city traffic, and how the engine is running, shakes sputtering etc.
Mike
Since you said 96 and LT1 I assume A4 and you said same fuel
that is a significant drop and it could be many things even stupid like dragging brake pad, low tire pressure etc but I believe you'd notice things like that.
So torque converter not locking, howis it running? Is it running rich black exhaust?---- bad O2 sensors, exhaust leaks, ignition problems etc
Did your state shift to a different seasonal fuel blend. I used to get crappy mileage when I was in Kali due to oxygenated fuels.
Basically its a shot in the dark until you add some other details, like road speeds, since TC lock won't give you that big of a mileage hit in low speed city traffic, and how the engine is running, shakes sputtering etc.
Mike
Last edited by aboatguy; Nov 5, 2008 at 09:14 PM.
Racer
Joined: Oct 2008
Posts: 299
Likes: 1
From: Ottawa Ontario
When I bought my 95 the previous owner said that he had to replace an O2 sensor every few years. He said he'd not notice any other issues like performance or anything but his fuel mileage would drop. Replacing the sensor fixed it every time he said.
Last edited by -=Tom=-; Nov 7, 2008 at 12:07 AM.
Le Mans Master
Joined: Sep 2003
Posts: 5,874
Likes: 0
From: Littleton CO
Does your locality have seasonal fuel blends? We do, and it's not (clearly, anyway) indicated on the pumps. The change from summer to winter gasoline here causes my daily driver to go down by 3-4 MPG, both on the dash and actual.
Happened within the last few weeks here, and it will be that way until late spring when it gets changed back.
Happened within the last few weeks here, and it will be that way until late spring when it gets changed back.
Race Director
Joined: Nov 2003
Posts: 12,221
Likes: 446
From: Overland Park Kansas
2020 Corvette of the Year Finalist (appearance mods)
C4 of Year Winner (appearance mods) 2019
O2 sensor, thermostat, and/or temp sensor are possibilities. In all 3 cases richer burn could be present.
Clogged cat, but you'd probably feel the difference.
Bad gas is another possibility.
Clogged cat, but you'd probably feel the difference.
Bad gas is another possibility.
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Cruising
Joined: Jun 2008
Posts: 10
Likes: 0
From: Penfield NY
one other thought might be whether you have recently "flashed" your ecm. some gm vehicles have experienced an "incorrect" gas mileage calculation that was fixed after the ecm was flashed with updated software to calculate mileage using a different algorithm.
