Poor gas mileage - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 08-02-2003, 03:21 AM   #1
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Default Poor gas mileage

I am Filling my tank up from E about once a week after ive drove 300 town kilometers or in miles about 180. What could be causing this poor mileage....ps its a SSEi as well but still thats not good at all....i replaced the O2 sensor and the mileage got a bit better...
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Old 08-02-2003, 03:24 AM   #2
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Are you using any octane less than 93?
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Old 08-02-2003, 03:36 AM   #3
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Lay off the SC... just kidding

Is it idling and or running rough if so you might have a bad spark plug.
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Old 08-03-2003, 02:19 AM   #4
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The best i can do here for octane is 91 and im using it. The spark plugs and wires are new, and yes it seems to run a bit rough at idel, and when its in park if i rev it up to about 2800 rpm or more it starts missing and backfiring.
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Old 08-03-2003, 02:23 AM   #5
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I don't know much...tryin' to think..but maybe injectors?

Ignore me if I'm out in left field.
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Old 08-03-2003, 02:34 AM   #6
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Yeah injectors might be dirty or bad might try some of that injector cleaning additive. But I noticed that right after I got a new battery for my car that I got a lot of misfires at about 3000rpm then the next day the misfires were gone, I still replaced my plugs.
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Old 08-03-2003, 02:51 AM   #7
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Could be something as simple as dirty air filter. If the car still eats gas after a tune up, then something bigger is obviously being a PITA.
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Old 08-03-2003, 02:54 AM   #8
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Oh yeah....guess I wasn't out in left field. Could actually be the injectors. I forgot....a long time ago when I was only getting like 220 miles a tank at most...I bought some STP Complete Fuel System Cleaner (gray bottle) and poured that stuff in the gas tank.

WOW!!!! I got >40 more miles to the tank! From 220/tank max to about 270/tank. You use it every 4,000 miles. That may work for you, especially since your wires/plugs aren't bad.

The second time I used it though I noticed a big drop in mileage for some reason, and it was over 4,000 miles later. I was worried, but changed my O2 sensor, PCV, and fuel filter and it was MUCH better.

I now get about 310/tank with a lot of city miles...and 390 highway (with some hard bursts to 105mph though).
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Old 08-03-2003, 03:00 AM   #9
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I tend to use STP cleaners as well. No complaints.
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Old 08-03-2003, 03:20 AM   #10
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Quote:
Originally Posted by bonnie94sse
WOW!!!! I got >40 more miles to the tank! From 220/tank max to about 270/tank.~~~
I now get about 310/tank with a lot of city miles...and 390 highway (with some hard bursts to 105mph though).
Wow I was getting between 320mi and 350mi/tank before I started any replacing/cleaning/modding and thats on an even mix of city and highway driving.

Quote:
Originally Posted by Allmachtige
Could be something as simple as dirty air filter.
Yeah I opened my air box up even after a mechanic said my filter was ok and there was all kinds of crap in there sand, bugs, and leafs. That stuff plugs filters quick.
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