Hi all,

Usually I just lurk, but my F-150 has had a serious drop in milage recently, and I wanted to check and see if anyone might have any tech advice on this.

Current config:
97 F150 XLT
5.4 L
K&N Filter
Gibson Super Truck Exhuast

Drop from 15-16 mpg down to 11-12 mpg. Have tried reset system computer, and varied gasoline to insure it wasnt just the gas at the place I regularly fill.

Anyway any tips or tech advice would be greatly appreciated.

My thanks

Rik
Denver

 

how many miles on the truck? you cold start with the obvious and do a tune up. change all the fluids (oil, tranny...), install new spark plugs, wires, etc... hope this helps, good luck!

 

I should have a major tune up done, all fluids are recently replaced, engine has 64K on it, will probably replace plugs wires etc.

Thanks!

 

I seriously doubt that a tune up will add 4-5 mpg back to your truck. I would look for something else which must be wrong.

 

OK any ideas?

 

Call the oil company and ask if they recently switched to "winter" fuel and see if that didn't correspond to your drop in mpg.

 

I'll assume you've cleaned and re-oiled your air filter.

Did you take a q-tip and carefully clean the two little wires in the MAF? Sometimes oil from the K&N can coat those and indicate false readings to the computer.

Has a baffle broke loose in your muffler blocking exhaust gases?

Yes, as posted above, plugs, wires, etc... tune up.

 

Have you changed tires? If so the odometer could be giving you a false reading, which would throw your calucations off.

 

* Filter cleaned and oiled.

* Muffler seems OK doesn't appear to be a blockage as exhuast gasses are passing from the outlet at what I would assume to be normal amounts.

* Tires the same.

MAS Airflow sensor! there's one I didn't think of will inspect it imeediately and post findings.

Thanks very much gang!

 

Oh yeah it was winter gas before too, so its still winter gas with the 10% ethanal and additives to prevent ice...etc.

R

 

I forgot to mention that you need to dip the q-tip in windex or similar type cleaner to clean the sensor wires in the MAF. Be careful those wires are delicate.

 

It could also be a bad O2 sensor. I had a bad O2 sensor that was not coding the computer and never turned on the "CHECK ENGINE" light. After I took it to the dealership they said they didn't understand why it didn't code the computer. Mine also had a rotten egg smell from the exhaust.

 

Increase your tire psi to compensate for the colder air--reduced air psi if you haven't already done it.

No one has mentioned your fuel filter--supposed to be changed every 15,000 (I think) miles. If it's clogged, that usually results in reduced high rpm power but it might affect your mpg too? Worn plugs will usually show up with hard staring but could be the problem too--not going to be fun changin' them rascals .

Dan