I have a big problem with this cars Fuel economy.I drive mostly Highway driving with cruise control with as little acceleration as possible and after changing the O2 senso I did not notice any drastic increases. The air filter is clean,tire pressure good. What is wrong? Can Some body please tell me what is wrong here.

Ensure the O2 wire is not touching any of the plug wires. This is sometimes an issue.

Please share other things with us about your car, maintenance records for instance. When was the last tune up of plugs, wires, maf and TB cleaning etc?

Those are great questions. MAF was done a few months ago.I actually don;t know when a real tune up was done last I'll have to ask my father. If I had to guess though longest it could've been was 2 years at absolute longest.

Ok So far I have learned that in September 07 the ignition coil was replaced along with the plugs so that was a while ago. In 2006 the throttle position sensor, throttle plate gasket and idle arm control motor was replaced.Alternator was replaced that year as well. SO apart from the many oil changes and brakes done and keys getting replaced that is everything of value to this investigation. Also My records say that the supercharger has had synthetic oil and that has been done a few times. If someone has any ideas that would be great.

Wait according to the records the last time the supercharger had new oil was sept 06. Would that kill my the mph. I guess I have to get on that.

Check your fuel pressure regulator, fuel pressure, injectors, fuel filter.

check/replace spark plugs, test/replace plug wires, test coils.

Check coolant level and thermostat.

Check/replace PCV valve.

One or more of these should be the problem.

Edit, supercharger oil should be fine. But if you want to change it, you can. Most of these tests can be found in the tech info area.

I have had similar problems over the years with my Bonne. The first time this happened (many years ago), it was an almost completely clogged fuel filter, literally gunked up to almost being closed shut. I was down to about 16 mpg highway when that had happened, so I changed the fuel filter and away went the problems.

The second time it happened, about 6 months ago with the car at 145k miles, I thought AHA another fuel filter. Swapped out the filter, but the problem did not go away. Took the car to the dealer and evidently I had rusted, leaking fuel lines. My car spent the vast majority of its life in the Northeastern part of the country, subject to road salt and all that (plus it is my primary winter vehicle) so I saw the lines after they were yanked off the car. YIKES! They looked like brittle twigs. After the fuel lines were completely replaced, everything has been great since.

Maybe look around under the car for any little "puddles" and sniff them for fuel? I had noticed that with my car, but assumed it had been with the connections to the fuel filter as opposed to the fuel lines themselves. Evidently, it was dripping straight from the leaking fuel line. Soooooooo.... fuel filter, fuel line??? What part of the country do you live in? I am far from a master mechanic, but have lived through a very skewed MPG situation twice, and both times was fuel delivery system related.

Good Luck

I live on Long Island. If it were the fuel filter though wouldn't I notice a drop in power?

I did have a slight hesitation when it happened to me, and a slight power loss. How many miles are on the car? Did you ever have the fuel filter changed?

Your post just struck me because I was getting terrible gas mileage and the new fuel filter took care of it. The other part I wonder about is a fuel leak. I am guessing that since we used salt on our roads (in PA), that in NY I would wager you use salt as well.

My Bonne is a '96 SE and it spent the first 10 years of its life in PA winters. 2 years ago I have to replace all the brake lines that had rotted out, from weather and salt. Last year I had to replace all the fuel lines that had rotted out, from weather and salt. I am sure there are tons of people on here who can offer better advice than I can, but I would still suggest sniffing around under your car.

Given the age of the car, and given where you live, I do not think a bad fuel line is out of the question. Of course, I spent $400 in having all the fuel lines replaced, so I would suggest the $20 to change the fuel filter yourself. Assuming of course it had not been done in recent memory. I think a $20 risk is well worth the reward, assuming you have eliminated other options first. Do you know when and if it was changed, and how many miles you have on your car?

The Car has about 160,000 and as far as I know from my fathers records of the car it hasn't been changed.He'* only had the car since 06 I believe. So it probably does need it.