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1987-1991 Parley with regards to your 1987 to 1991 Bonneville, Olds 88 or Buick Le Sabre Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 10-25-2004, 10:18 PM   #1
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Default MPG dropping

I used to be able to drive to school on a quarter of a tank, now its a half a tank, i changed the air filter, but nothing. I am also approaching 100,000 miles. Just wondering what should/needs to be done at the mark, and if that would help my MPG too.
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Old 10-25-2004, 10:22 PM   #2
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O2 sensor, PCV valve
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Old 10-25-2004, 10:26 PM   #3
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Tune up bud.. also check your vacuum lines. If your '90 is anything like my 89, they are all rotted, and are worthless. Fuel filter isn't a bad choice either, and grab some seafoam while you are doing that.. great stuff, I swear by it!


-justin
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Old 10-25-2004, 10:37 PM   #4
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Quote:
Originally Posted by opensourceguy
I swear by it!-justin
Now, now....no swearing on this forum But all seriousness aside. The *Oh-Two* sensor is a Must. Just make sure you stick with an AC-Delco O2 unit and you won't be coming back here a few months later saying that your gas milage sucks again. If you don't know when the other stuff(plugs,wires, gas filter, pcv valve) were ever changed, you should change those as well. Let us know if you see an improvement.
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Old 10-26-2004, 12:52 AM   #5
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after all that, u might want to look at your tires, and how big your collection of useless items is in the trunk. then look into suspension like how the struts are, and when the last time an alignment was done. check the cvboots too. if those things are drying, they will slow the car down. tranny flush? oil change <different type then than now>, tire pressures, stuff like that. have u noticed a change in travel rpms, or do u know.
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Old 10-26-2004, 02:25 AM   #6
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Tires are pretty much brand new, construction going on behind my house. The tranny was just flushed with new cv joints/boots, so theyre good. I have been using Valvoline Max Life and that seems to work well, anything better? When I am running 75-80 mph its about 2300-2500 rpms or so. It has seemed to always be there, seem right to anyone else? I dont know when anything else was changed so I was going to go through pretty much about everything that needs to be changed. Start off all brand new. Anything else???
Thanks for the input
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Old 10-26-2004, 03:22 AM   #7
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ever thought of going full synthetic w/ oil. that is some mean stuff. my gas mileage went up 2-3 and the car ran smoother and cooler. try it next time.
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Old 10-26-2004, 07:43 AM   #8
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Yeah.. no wonder your MPG is horrible. You are sitting at 2500rpm at 75. I can do 85-90 at 2000 ish.. if I put on the cruise. Sounds like you don't have TCC lockup.. or you aren't going into OD.. more probably TCC, because 3rd gear at 75mph.. wouldn't be 2500.. it'd be much higher IMO.


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Old 10-26-2004, 11:54 AM   #9
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It kicks into OD, I know that much. So what entails fixing the TCC? How would running 200 or so more RPM'* going to cost me an extra quarter of a tank? Seems like a combination of a lot of stuff, am I right?
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Old 10-26-2004, 02:42 PM   #10
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Are you keeping any sort of mpg records ? Could be something as simple as turning the a/c on. However if you have not changed your habits, something else has. Could be ignition, could be clogged injectors, could be O2 sensors, with fall coming on it could be a stuck thermostat.

Are there any trouble codes ? Is the block learn multiplier (BLM) reading high ? Is the system in closed loop ? All things needing to be checked to answer your question.
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