If you remove the gas cap the mileage goes back up. Checked all the usual suspects. Changed upstream O2 sensors. MAF tested fine.
Any Ideas.

 

what is the mileage on your truck? is the CEL on? how long have you owned the truck? has it always had 4mpg or has it just dropped recently? when was the last tiem you did a tune up? and what did you do for a tune up?

 

Are you getting a code? Where are you getting 4mpg from, a scangauge or from mileage/fill-up gallons? How did you figure out the gas cap off mileage? I don't think the engine could run that rich and not spit out a code or 3.

 

or like 10 codes... or a hole in the fuel tank

 

You need to change all 4 first...

 

I have never understood why it is always recommended to replace all four O2 sensors. The front sensors are what control fuel mixture, and the rear sensors are simply catalyst monitors. The rear just tell the ECU how well the converter is working.

 

I am with you on this as i will never understand all the bullsh$it i have to do on the POS... but seeing as you can get 02 sensors for $20.00 a piece, it make sense so you can rule out the obvious bullsh#it...

 

Where did you get 02 sensors for 20 bucks? are they the right ones?

 

I wasn't going to say anything about that, but... I paid $50 each for my front sensors (Bosch) and that was at wholesale cost plus a buddy discount!

 

I'm sure you could find sensors for $20 a piece, they are just happen to made from wood.