I normally average 15 mpg. I have suddenly dropped to 13 mpg. Nothing has changed mechanically and no codes. I think the O2 sensor are going bad. My questions is which ones, do I need to change the front or rear sensors or both.

 

fuel filter changed lately?

 

winter fuel mix where you live? Oxygenated fuel? That would do it.

 

I lost 3 mpg just because of winter fuel mix

 

I wouldn't worry about 2mpg. It could be from just a different pump that clicked out later. Mine fluctuates 2 mpg every tank. If your outside has dropped in the past how ever many days and it is taking longer to warm p that will also cause it to burn more fuel as it is burning rich trying to warm up.

 

if i neglect to change my oil my fuel mileage takes a dump big time if i go too long.

 

Its either winter fuel, o2s, or clogged cats.

 

That's what I was going say

 

You put the Magnacharger on at 170k so did you put the Denso plugs in at the same time and how many miles do you have know? How did you get around a tuner with that Magnacharger? With all that said I would clean the MAF.

 

Yep, winter fuel is the answer I'd say-both of our's are down, too. F150 looks like it's down 2 mpg and I'd say that the Honda Pilot is down a couple of miles, too. Welcome to winter.

 

Mine just dropped by about 2mpg too. It does every year about this time.

 

Thanks for all the quick info. It has a fresh fuel filter, changed at last oil change. I have 272,000 miles so far (100k with the blower). Rebuilt the Magnacharger (it runs a FMU with stock injectors) and tranny each once but still original motor. I change the Denso's every 50k miles. I check fuel mileage just about every fill up. It has always been pretty consistent year round. It is actually a little better in the winter compared to summer with the blower on it. Don't know if we have winter fuels in Tennesse. I probably need to change out the O2's with this many miles anyway.

 

My mileage is dropping too - because Missouri is switching over to E10, mandatory by the first of the year. A lot of stations have already switched.

 

they just can't leave it be..

 

I am having the same problem with my 97 4.6. I pulled a code saying I was running lean on the left bank. I was told to replace spark plugs, and wires but I also need to check for a vacum leak and have my MAF sensor re-calibrated.