Gas Mileage Suddenly Dropped! HELP! - 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 03-01-2003, 02:38 PM   #1
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Default Gas Mileage Suddenly Dropped! HELP!

I used to get around 22 around city now I get FIFTEEN! That'* worse than my dad'* V8 1500 chevy truck! grr! Help!
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Old 03-01-2003, 02:39 PM   #2
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Any codes? CES lite on? If not, your O2 sensor may be starting to go!
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Old 03-01-2003, 02:45 PM   #3
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No codes or lights so far. I think it'* the O2 sensor as well. I don't believe it'* the MAF screen removal, since it ran fine for two tanks afterwards.
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Old 03-01-2003, 03:10 PM   #4
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maybe it'* that 180 degree thermostat
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Old 03-01-2003, 04:18 PM   #5
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The 180 won't affect your mileage at all. The MAF screen can, however. A higher volume of air can require more fuel to keep the ratio correct. It can take some time for the PCM to re-learn, so those two tanks that it was fine might have been while the PCM was slowly adjusting the AF ratio to compensate for the higher flow of air.

That should be minor, however, compared to what an O2 can do. If you're at around 50k on your old O2, that should be your starting point. This is assuming the other 'basic tuneup' items are confirmed. Plugs, wires, etc.
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Old 03-17-2003, 10:22 PM   #6
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Any chance you have a neighbor with a syphon hose and a sense of humor?
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Old 03-18-2003, 12:03 AM   #7
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Ok son! I'll ask you what my dad use to ask me...what is the last thing you did to the engine before the trouble started. Think hard about this.
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Old 03-18-2003, 12:18 AM   #8
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Is $62 too much to pay for an O2 sensor. It was at NAPA, or should I go to the GM dealer I got in town?
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Old 03-18-2003, 01:50 AM   #9
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Are you positive, cause I put it in and it came out as an O2 sensor, but how come it doesn't say for what type of vech., it'* not like I don't belive you I just want to make sure. Ya I know I'm picky!
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Old 03-18-2003, 04:07 AM   #10
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Jr has been researching this ever since my book was proven wrong. He also has the same one as you. (actually, he'* been putting this list of applications together for a couple weeks now)......trust the numbers. I've been dishing out part numbers here for quite awhile, and I've only been wrong once so far!
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