About 3 months ago, I started having very poor gas mileage. Was getting 360 or so per tank, now only getting 240 per tank. The only thing I changed was a new set of rear tires which I've confirmed are properly inflated, balanced and aligned.

I did get the recommended fuel system cleaning, have had the oil changed recently and replaced the plugs (though it didn't look necessary). Do I go for replacing the O2 sensor(s)? Kind of expensive for just a shot in the dark. Please help, can't afford to drive it!!

 

You should diagnose before throwing expensive parts to fix the problem.

The ECU reads several different sensors to adjust the amount of fuel injected. I would suggest either having a shop use a scantool to read the various sensors or get your own to do the job.

 

I doubt you need o2 Sensers. Weather could play a role in bad fuel economy, bad gas, driving habits, fuel filter, winter grade gas and so on. Clean out your throttle body that should help a little also.

 

also check your intake (air filter) and make sure your oil change is recent.

 

Check brakes are not dragging by lifting and rotating wheels by hand. Front wheels should turn w/modest effort from one hand. Rear wheels should be easier (no axle/differential to turn).

Is this a 4-cyl or 6-cyl. engine? Add to your signature line.

good luck

 

The car is a 2005 Accord EX V6. Am on the way to pick it up from the shop. They ran diagnostics (for $100....) and found absolutely nothing wrong. The mechanic suggested it's the ethanol in the fuel today but 100miles per tankful sounds like a huge decrease for that. It does get a bit better with fuel additives but not a bunch. Will check tire rotation, brakes, etc. and get back to ya.

Thanks to all for your help.

Slow Eddy

 

Do you have an auto-starter? Do you warm it up? All city driving? Lead foot?

 

** Very good point here, warm weather..cool down re-mo starts waste your gas...poor miles per gallon...**

WheelBrokerAng

 

My 2000 V6 got about 18 MPG. I only drive 10 miles a day during the week. The car had an auto-start and although I intended to give it 5 minutes, it wound up getting more like 15. I hit 7000 rpms almost every time I drove it, it was dyno tuned and had bolt-ons.

Now, I have a MT Scion. It gets 25 mpg. I can't hit 7000 rpms because my redline is at 6200. I don't have to rev it out all of the time because it has more low-end torque than the open diff and FWD can put on the ground. No auto-start and hardly any mods ..... for now.

 

Lots of good questions/advice here.

I am a bit of a leadfoot but that has calmed down due to the mileage decrease. With regard to weather/temp, this started in June here in Florida and has persisted so it has been quite warm the whole time. It's just starting to cool down now so will look for a change in mileage.

I did take the car to a shop where they checked codes and found absolutely nothing. Their belief is it's the ethanol we add to everything down here. Guess that's possible. Still haven't checked to see if all tires spinning freely and haven't cleaned throttle body but those will get done this weekend. These guys agreedit would be unlikely that the O2sensors are bad and probably not worth the money to change them. They suggest I start adding an octane booster (their's of course).

Last oil/filter change was exaclty 3000 mile ago so I don't think that's the cause since the decrease started right after the last change.

Thanks everybody.

FE