real poor gas millage. what could it be? anyone? - Page 2 - 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 08-01-2007, 08:32 PM   #11
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Its good enough to use for a bit but has been known to go bad fairly quick, they don't last the years & years that the Delco'* do.

We're all assuming your Service Engine light isn't on. If its on please go get it scanned, usually free at the parts stores if they can do your year (94 and 95 are oddball years btw).

On the subject of the gas leak; gas dries fast! My wifes car (the Olds in my sig) was leaking and left no drips in the driveway, You'll want tolook at your lines under the passenger side for any wetness (areas darker than the rest of the line) esp in the rear by the fuel filter. You have more than one line to check; theres a feed, a return, and possibly a vent (I'm not sure on your year)

If the O2 doesn't help, I would look at the Coolant Temp sensor(CTS), If that is out of whack or been replaced by a "performance chip" then your car will always be running in 'cold' mode with poor gas milage..

Lastly, many of the items you replaced can be tested to determine if they are bad. If you haven't, pick up a cheap Haynes/Chiltons manual. They have decent sensor testing procedures that usually only require a cheap multimeter to perform.
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Old 08-01-2007, 09:16 PM   #12
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Generally we find that the Tachs are off by 150-200... so the actually idle is closer to 750 Give or take a few.. It sounds like you are on the money for idle..

For the O2, for the 94,95,96 model years they all use the AFS 75 Sensor.. But they seem to drop off in performance after 60,000 miles.. I have seen cars go from 24-25 in mixed driving to as low as 18 in the same driving situation..

Example in the city would be like going from 20-21 to 15..

More than most if the car is fairly well tuned and the mileage is still stagnant then it may be due to the O2.. I have seen them just about 90% dead, and the PCM won't thow a code till its almost time to throw the paddles at the O2..

I do not like the Bosch at all... But if it was a free sensor to you than you may try it, as it may function ok for a while and improve your mileage.... But I do recommend that you get an AC Delco or Denso unit when the $$ allow...

The Factory rating for a 95 Bonneville SE with the 3.06 Ratio is 19 City and 29 Hwy... I do 17 to 21 and 28-32 depending on my driving habbits

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Old 08-05-2007, 01:40 PM   #13
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what about a clogged cat? Change the oil and trans fluid. does it have a code 41(missing the magnetic interupter in the cam sprocket)?
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