92 LeSabre Horrible Gas Mileage
 

Can bad exhaust O2 sensor cause 15mpg?? Any thoughts?

Yes, If it causes the computer to make the injectors compensate for a vacuum leak thereby causing a richer mixture.

Thanks Hanky. I fixed the O2 sensor on the exhaust manifold and now i will check my mileage and see if it gets any better... ill post later.

There are many things that can cause your mileage to go south. One of them believe it or not is a battery that is also going south, (getting tired).

My voltmeter is reading close to 16V (just on the edge of red) I didnt think much of it because the car is older and thought it was a little off....

FYI, i hadnt driven this car since last summer and was consistently getting 28mpg with it.
I might swap batteries and see what happens..... thanks for the help.

Doesn't it make you wonder?
You buy a new car today and the mileage isn't much better than some of the older ones, but now you just spent a lot of money for a new car with supposed better mileage.

Yah "supposed" better mileage... I know i wont spend the money.... not to mention i would rather tinker with my car anyway.....

Any other things i could check out while im at it? Think a new fuel filter would help/necessary? just trying to find other things to look for when the 02 sensor and battery dont fix my issue :)

There are many tinkerable things for you to tinker with. Like here we go;
1. Air in the tires
2. Air filter
3. need new spark plugs/wires
4. Usually the oxygen sensor doesn't go bad if the car isn't used
5. We do manage to get better mileage in the summer compared to winter.
6 Are you driving with heavier shoes/boots? (heavy foot)
7 Is the engine getting up to correct operating temp?
8 It never hurts to have a clean fuel filter
9. Sometimes the mileage will improve through use.
I don't know what part of the country you're in so I cant blame the cold.
If you plan on keeping the car , I would invest in a scan tool that gives you "data read out" that way you can see things like injector pulse width, short and long term fuel trim.
They can tell you much more than me babbling on and you would be surprised how much you can learn about how the engine is performing. If you like tinkering you will love to see the different read outs you can get and diagnosing things like poor mileage are so much easier to diagnose. One of the most important things to have is a factory manual. Always worth the investment. Check out "Helm Inc".com
Now that I have spent some of your money, don't you feel better?

Pull the codes...still probably OBD1...
 

Have you pulled the OBD1 codes yet....that's the 1st plan of action...:)

I have a 1989 Buick LeSabre 3.8 L...I'm just getting to know where the ALDL is located...starting to track down my low end power & acceleration...:o

It's generally being a trouper (229,500 miles) but I had to give attention to another vehicle for a while...it's the wife's daily driver...get about 23 in the city...31 on the hways...
until just recently....higher gasoline prices has my wife mentioning to improve her ride....:rolleyes:

I did work on a replacement EGR valve as suggested by my mechanic (consulting) from the 'bone-yard'...;)

Prior to that...it was whizzing when the accelerator was mashed...creating low power & speed...increasing heat...my vacuum hard plastic tube even melted....:eek:...causing the HVAC to stop working...etc.
https://lh6.googleusercontent.com/_N...8/DSC02207.JPG


Yesterday, while looking for the ALDL...(I think I saw it under the ash tray area after dropping the lower dust cover...I just couldn't believe it was so cheap plastic looking...)....I decided to replace the pintle (IAC) valve...again one from the bone-yard...
https://lh3.googleusercontent.com/_N...0/DSC00111.JPG

Notice: I did not double check the donor vehicle 'year'...so even w/the same 3.8 L engine...these pintles are not inter-changeable....:rolleyes:

https://lh4.googleusercontent.com/_N...0/DSC00123.JPG

I had to clean the original pintle w/brass brush...& use it until I can again source a compatible unit....The cleaning to remove the carbon build-up did infact help greatly w/the lack of low end power & acceleration...:)

I'll push for more when this wet spring sudden snow fall clears in a day or two....

More later

Good thing you noticed the difference in the pintle design thereby making them not interchangable. Did you get a chance to clean the throttle butterfly and the IAC passage?