33% improvement in 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 10-10-2005, 05:31 PM   #1
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Default 33% improvement in gas mileage

Changed the O2 sensor (AC Delco) in the '95 SLE. Mileage went from 18 to 24. (65 highway 35 city) While in the process of changing the sensor, I checked the back pressure on the exhaust for a plugged cat, but at 2500 rpm, I got less than 0.5 psi, so that was clearly not the problem.

I have been running for a while now on my disconnected knock sensors and 99c resistor fix, and have pretty much decided to make this engine a test case for what happens when you do this. If I come across a good deal on an L36 drive train, I may change it out and autopsy my ticking engine. Or, I may just wait to see what happens to this setup.

If you're getting lousy mileage, and your O2 sensor is old, you may want to consider a change.

[edit: that was 65% highway 35% city on the driving mix]
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Old 10-10-2005, 06:15 PM   #2
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65 highway? Ummmm.....you need to replace the batteries in your calculator.
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Old 10-10-2005, 06:26 PM   #3
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I think he meant he traveled 65% on the highway...
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Old 10-10-2005, 06:29 PM   #4
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Quote:
Originally Posted by jwikoff99
I think he meant he traveled 65% on the highway...
Or 65 linear miles.
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Old 10-10-2005, 09:21 PM   #5
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24 combined is about right.
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Old 10-10-2005, 10:56 PM   #6
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Default Re: 33% improvement in gas mileage

Quote:
Originally Posted by bill buttermore
If you're getting lousy mileage, and your O2 sensor is old, you may want to consider a change.
[edit: that was 65% highway 35% city on the driving mix]
How hard is it to get the old sensor broken loose? I have 128K on 98 3800 motor. How can I check the sensor before replacing it?
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Old 10-10-2005, 11:14 PM   #7
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how much for the o2?
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Old 10-11-2005, 12:07 AM   #8
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No very worst comes to worst use pb blast,but I would make sure the car is cool (not sure if the stuff is flamabe). I had 94 corica that is was so rusted it was hard tell weather 02 was suppose to come out. Got eventully
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Old 10-11-2005, 03:26 AM   #9
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It is supposed to be easier to remove when it is warm. Remove the strut brace first for really easy access. I bought a special split socket for the O2 sensor and I did not have too much trouble removing it with a 3/8" drive flex handle about 13" long. I paid $59 + tax for the AC Delco sensor at a local parts house. I think the torque spec for the new one was in the neighborhood of 13 ft-lb.

I read elsewhere on this site that if the O2 sensor is black or sooty, that it probably is letting the engine run rich and should be changed - normal color is gray. I think they are only good for about 60K.

BTW, I could not tell much difference in the scan tool data between the old and the new sensor, or in the performance of the car, but the mileage certainly improved.
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Old 10-11-2005, 09:53 AM   #10
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60K?

Ruh roh.

123K and I've never changed it. I guess I better take a look.
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