1992 SE bonnie getting horrible 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 10-16-2009, 03:14 AM   #1
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Default 1992 SE bonnie getting horrible gas mileage

I have 183k miles, I've had the car 6 years. My motor sounds like crap, my lifters tick and I think I have a misfire, the car runs a little sluggish, not very smooth and I used to get a combined 21mpg and now I get 12-14mpg regardless of whether I drive highway or city I still only get 14mpg tops. Well this is getting pretty expensive on gas. I have a/c delco platinum plugs in the car, I pulled one and it looks fine. I replaced the spark plug wires. Anyone have any ideas on why my motor would be running a little sluggish and be getting horrible gas mileage? My check engine light is not on, I've been considering doing a whole motor swap since I can't figure out the problem but I don't think my motor is completely shot, it still runs somewhat decent
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Old 10-16-2009, 08:34 AM   #2
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Pull all the plugs and check them. Clean your MAF and throttle body, how old is your O2 sensor? That may need to be replaced.
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Old 10-17-2009, 04:27 PM   #3
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I had to replace the TPS (throttle position sensor) twice on my 92 Bonne within three years. Failing or improperly adjusted TPS can hit your fuel economy pretty good. Its easy to check with a scan tool but a good multimeter can also be used.

Transaxle issues can also impact fuel economy, and the symptoms can deceptively point to the engine. I drove my Bonne for several hundred miles with an intermittent problem that I thought was the engine running roughly or misfiring at highway speeds. Turns out it was the transmission. The torque converter was intermittently slipping at highway speeds while in overdrive, making the engine seem to run very roughly and lose power. Rebuilding the trans and replacing the controller (I forget what its called) not only solved those issues, but hugely improved fuel economy. This can be confirmed with a scan tool that will show the torque converter RPM fluctuating when it should remain stable.

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Old 10-18-2009, 03:52 AM   #4
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thanks, I'm going to change the plugs and keep going from there
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Old 10-21-2009, 12:56 AM   #5
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I changed my spark plugs and it fixed my misfire and my car is now running really good again. I had 1 plug that was really bad but the rest looked fine. I'm super pumped, thanks bonneville brothers!!! haha
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Old 10-21-2009, 08:01 AM   #6
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Check that plug again in a week or so. If it'* going bad again you will need to look in to why.
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Old 10-21-2009, 09:11 PM   #7
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look at your tires; i was running into the same problem turns out my tires were low i pumped them up i got 2-3 mpg more
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