fuel economy issue - 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 03-09-2005, 03:51 PM   #1
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Default fuel economy issue

1993 Bonneville SE (NA):

Within the last 4-5 months my fuel economy has gone to hell (12-18 mpg). The only change that was made was two oil changes and a radiator swap from a 96 SE. The radiator is smaller, but cools differently. I don't think that has much to do with it.

There are no signs that the fuel filter has been changed anytime recently. The serpetine belt is showing signs of wear and needs replacement. The air filter is almost 1 year old (or 50,000 miles). Engine was replaced at 127,000 miles with a Jasper and odometer is now at 165,000. Plugs were changed with the engine, but wires are original.

Anything else I should take into consideration?
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Old 03-09-2005, 03:55 PM   #2
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What is your year and trim level?

How old is your oxygen sensor? An old oxygen sensor can cause gas mileage to tank.
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Old 03-09-2005, 04:08 PM   #3
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Sorry, my sig didn't work for some reason. I edited with the info.
O2 sensor may be original, and I have been told that before. I will take a look at it and see what I can make of the dating.
If an O2 sensor were bad though, wouldn't there be other issues? Or does the computer just adjust to compensate for incorrect input?
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Old 03-09-2005, 04:21 PM   #4
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Fuel filter won't cause poor mileage.

If your O2 is over 50k miles old or unknown, change it. AC Delco ONLY. Particularly NO BOSCH. They don't last in our engines, and can make your problem worse.

Your O2 may not have other symptoms other than mileage. They get tired, and need to be replaced.
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Old 03-09-2005, 04:55 PM   #5
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The O2'* on these cars can become almost dead without tripping the SES light... When I had a second one tank on my 95 I scanned it and noticed that it was not comming up to temp quick so that it would start giving the cars computer an accurated reading of the oxyogen content of the exahust... On a scantool you can see the O2 in voltage ot watch it swing back and forth between lean and rich... It should change fairly rapidly, lean rich lean rich lean rich... If it stays lean lean lean rich lean lean lean lean, rich rich, lean lean lean... Then its getting very very slow... This can kill you fuel effiency...

I will reccomend that you replace the plugs and wires, get some NGK TR55 spark plugs, a new air filter, and replace the O2 if it has not be done... And as Will stated, stay away from the Bosch, get the AC Delco Unit... Also is your O2 sensor a 2 wire or 3 wire unit? 3 wire would be the heated O2 sensor...

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Old 03-09-2005, 04:57 PM   #6
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He may also have a 1-wire. Mine is.
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Old 03-09-2005, 05:05 PM   #7
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Quote:
Originally Posted by willwren
He may also have a 1-wire. Mine is.
Yeah 93 was an odd year... so far it seems as is all of the NA applications used the 3 wire heated( most of them anyhow ) and all of the SC'd applications used the 1 wire.. That might have to be tacked on the the research list

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Old 03-09-2005, 06:03 PM   #8
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I will let you know how many wires this weekend. It will take some time to check all of this stuff out, but I think I can get either the 1 or 3 wire variety for AC Delco even if I have to special order it. Is there something I should know about one or the other?
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Old 03-09-2005, 06:24 PM   #9
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I just talked to the guy who usually gets my parts and he tells me the O2 sensor that was originally installed is a Delphi. Should I believe this?
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Old 03-09-2005, 06:35 PM   #10
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I just got off the phone with an official AC Delco retailer. We will see what they say about the O2 sensor when they call back.
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