authoritay

I've got a 2001 F150 4x4 4-door, 5.4L with 125k. Up until it hit 110k miles, I averaged about 14-16mpg. For some inexplicable reason, my MPG tanked and hasn't come back up. I replaced all the plugs and COP's, replaced the MAF sensor, and did a hard reset on the computer. The first time I did the computer reset, my MPG went back up ( I took it on a 300 mile trip last summer and it held steady at 16mpg.) I pulled my 25ft travel trailer and the MPG went back down (to around 8-10mpg.) And, now, towing or not, it stays at 8-10mpg. I took it to a local shop last month and the only issue they could find was the "lazy O2 sensor" which they replaced, and a heater core issue which they also replaced. But still, I'm getting only 8-10mpg.

Since the dang thing isn't throwing any codes, I can't figure out where to start looking. I thought maybe my brakes were dragging, so I'm doing a complete brake job next weekend (new rotors, calipers, pads, and lines.) But, if that doesn't do the trick, I'm at a loss. Any suggestions?

Fordfan2006

What brand of plugs and coils did you use?

the01kingranch

Well for one thing I can tell ya brakes are not the cause. Not sure how you were getting 16 mpg unless it was 60mph cruise on highway

w0lvez

READ THIS https://www3.epa.gov/otaq/models/mov.../420r14014.pdf

Jbrew

So your getting a brake job done regardless. Have you checked for drag ?

Are you using additives, - snake oil in the tank by chance ? Yea additives cans screw the plugs up, possibly bridge them. Are you using Motorcraft plugs, Motorcraft or Bosch O2 sensors ? You were getting good mileage, almost unbelievable, are you sure your figuring right ? Who's gas are you using ? Perhaps you got some bad gas, try another station.

white89gt

That's a little personal, isn't it?

Jbrew

Doesn't bother me, - my gas is GREAT!

Frank_Ford

If your engine is running cold (like with a low temp thermostat or the thermostat stuck open) you will get a cold reading off your temp sensor and more fuel will be pumped into the engine. Check for bad sensor, bad thermostat, since you said that you already had an issue with the heater core.

tcrote5516

That would have thrown a code and an idiot light for insufficient engine temp.

jprevat

iTrader: (1)

This is going to sound stupid but check your plugs. I had one back off and the small loss in compression was good for 2 mpg.