I purchased a 2004 F150 Supercrew XLT 5.4l, 3-valve in August 2012 to pull my small 3,000lb travel trailer. At that time I was getting 17-18mpg on the interstates with just the truck. Adding the trailer and mileage went down to 12-13mpg. A month ago gas mileage began to drop off so I had a Ford dealer do a tune-up. They changed plugs (broke 4 of them!) cleaned injectors, induction cleaned throttle body, plus changed fluid in the rear end. No improvement, mileage continued to get worse. I now get 12-13mpg truck alone and 8-9mpg towing the RV. Engine and tranny fluid levels are all normal. I am far from home, in Texas, travelling to California and gas is costing a fortune, not to mention that there may be something very wrong with the vehicle. I intend to get it to the Ford dealer near my current RV park but I wanted to get some ideas from the forum before I go. What could be causing such a drastic change? I not only lose mpg but power too - almost any hill will cause a downshift from OD and it just feels sluggish? I hope that I have given enough info to get some thoughts from the forum.

 

How many miles? Changed fuel filter? Does it shudder if you roll into the throttle around 45mph in overdrive?

 

Also any after market intakes or anything?

 

I am having the fuel filter replaced tomorrow, Jan 2. No shudder at all.

 

no after market anything

 

What gears and tire size?


Pulling in headwinds?

 

Gas mileage keeps dropping. Picked up a new 12' F-150 Ecoboost. Mileage climbed to 18.6 after a month, then keeps dropping, 3 months later, now at 17.3....that sucks.

 

Have them check the injectors for leaks and check the cats.

 

Sounds sort of typical to me. you always get worse mpgs with the cold winter air/winter gas blend/longer warm ups. and if you are over here in the west, you are probably going up into higher elevations which reduces o2 and power.

 

Excessive loss of fuel mileage (4mpg). Thread Summary:

11 fill-ups prior to November 1 average HIGHWAY miles = 17.3mpg
6 fill-ups in November and December average HIGHWAY miles = 13.5mpg

December 11: Tune-up at Ford dealer in Daphne, AL (induction cleaning, injector cleaning, replace spark plugs. No improvement)

January 2: Fuel filter replacement, Ford dealer Conroe, TX (No improvement)

January 3: Systems diagnostics, Ford dealer Livingston, TX (Computer upgrade downloaded from Ford. Subsequent diagnosis showed no faults found in engine or tranny)

How many miles? (91,000)

Also any after market intakes or anything? (No after-market anything)

Changed fuel filter? (Yes)

Does it shudder if you roll into the throttle around 45mph in overdrive? (No)

What gears (.373) and tire size (P265/70R17 - but these are not an issue because they have not changed)

Pulling in headwinds? (Only during one tankful of the 17 fill-ups since September)

Help!

 

A 4MPG loss with winter blend fuel isn't really 'that far out of the park'. I've seen worse and better depending on many things.

 

It turns out that the problem was a frozen hydraulic adjuster for the timing chain - the timing chain had become looser as the miles piled up. Computer could not compensate. New adjuster, new chain and new phasers got my mileage back up. Thanks to all who contributed comments.

 

Interesting. I don't recall hearing one evidencing itself in lost mpg like that. Thanks for posting back your results.

Sent from my iPhone using IB AutoGroup