Gradual loss of gas mileage over 8 mo - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 02-07-2006, 01:50 PM   #1
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Default Gradual loss of gas mileage over 8 mo

Eight months ago, I was getting around 22-24MPG city driving. Over the last 8 months it has gradually dropped to 13.5MPG. I replaced the front 02 sensor about 3 weeks ago when I got a code that it was bad. I have 117,000 miles on my 99 Bonny SLE with 3800 engine. Any suggestions. Maybe plugs and wires needed or new PCV?
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Old 02-07-2006, 01:59 PM   #2
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i would start with a tune up, that seems to be logical step if the car has not had one in a while
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Old 02-07-2006, 02:15 PM   #3
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A good tune up will include plugs and wires if they are old. You can check your PCV valve easily to see if it needs replacing. Take it out and see if there is a lot of carbon in it. If so, clean. Shake it. If it rattles easily, it is good. If not, buy a new one.

Also, after your tune up, it helps to clean your MAF sensor and throttle body, especially with the miles yours has on it.
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Old 02-07-2006, 02:36 PM   #4
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Quote:
Originally Posted by lash
A good tune up will include plugs and wires if they are old. You can check your PCV valve easily to see if it needs replacing. Take it out and see if there is a lot of carbon in it. If so, clean. Shake it. If it rattles easily, it is good. If not, buy a new one.

Also, after your tune up, it helps to clean your MAF sensor and throttle body, especially with the miles yours has on it.
I agree 100%. PCV valves are like 4 bucks though.

Cleaning the MAF does help if it is higher miliage though and it has never been done, just be careful with those little wires.

what brand of O2 sensor did you change with?
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Old 02-07-2006, 04:19 PM   #5
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Hans;
I used the Bosch Premium oxygen sensor. May have been a bad choice after reading other posts about it.
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Old 02-07-2006, 04:21 PM   #6
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I was just looking where the PCV is on the car and I am at a loss. Where did they hide it on the 99 Bonny.
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Old 02-07-2006, 04:34 PM   #7
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I could be wrong, but I think yours is still in the same place as mine is. In the pic below, it is just to the right of the alternator, at the end of the Upper Intake Manifold, where the yellow connector is. PCV valve is in there.
This pic is looking from the pass. side of engine bay
Name:  bonne010706006.jpg
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If you are looking at your engine from the front of the car it is on the left side, see?
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Old 02-07-2006, 05:08 PM   #8
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Yes, that'* the location.
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Old 02-07-2006, 05:50 PM   #9
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Could the CAT be the problem since o2 sensor was bad, wont that give bad mileage.Also wondering for myself.t
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Old 02-07-2006, 10:57 PM   #10
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lash;
I found it right where you said it was located. Opened it up but couldn't get the PCV out easily. Had to put back together since I had to leave. Will try again tomorrow.
Hans;
I cleaned the MAF earlier today, looked ok but cleaned it anyways.

jdq;
What is the CAT, not familiar with all the jargon here as of yet.
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