even with no codes, tune-up from stem to stern. i ahve always only got 11mpg with my 1992 4.9l f-150. all sensors new in last several years. any clues???????????????

 

exhaust header leak, vacuum leak? im in the process of finding the same thing i get 11mpg MAX with my 95 my uncle got 17ish with his BEFORE he cut the cat out...if you figer it out before i do please let me know...i bout this truck cause all the 4.9s i know (theres a lot of em in my fam) all get fairly good mileage stock so it would be a bonus to grab some mps somehow

 

I get about the same milage.

My plugs burn white to grayish, but the exhaust smells rich.

I suspect it's in the computer.

 

mine smells a bit too sweet for my liking

 

ign. wires may be old, what brand?

plugs should be copper motorcrafts.

really not enough info from you.

 

plugs are copper motorcraft, wires are msd 8mm(have tried varies types over the years), plugs when i change them seem great, i am meticulous and timely with maintenance. she has always been this way. two years ago i thought of exhuast and intake leaks, so i replaced the intake./exhuast gaskets, all new vacuum lines and still 11mpg?

 

Makes my 10mpg F250 SC 4X4 w/460, C6 not seem so bad after all. How is your 02 sensor?

 

I was just about to ask the same thing, hows the O2 sensor.

How is the EGR system, is it intact and fully functioning? Granted only works at highway speeds but....

Fuel pressure to high? leaky injectors?

Does this truck have a auto or manual transmission? That mileage is low even with a auto, but if it has a manual its really bad.

Oh and hows the spark at the plugs look, strong bright white flash/snap or just a blue spark, or worse then blue a lazy weak yellowish blue looking spark?

 

auto or stick?

mileage?

o2 sensor may be a good thing to look at like has been said already.

 

ya i tried that on mine no diff but the old one wasnt too bad...hows your head gasket? it might be leaking a bit and the exhaust from that wil throw off the O2 sensor

 

do u have big tires? also what are ur gears at? sounds like ur truck is mechanically strong.. so if u have oversized tires it will throw ur speedo off and taht would put ur milage off with an auto trans and high gear ratios.. it could be reading that low for mpgs.. idk may be way off.. jsut an idea

 

oh also.. man lock outs? that will drop u about 1-2 mpg with auto lockouts and an auto tranny will drop about 2-3

 

o2 sensor is new as is the egr valve. it is an e4od 4x4 flareside. even when it had stock 235/75r15 it got this, believe it or not it has 33's on it and the mpg have never changed

 

It sounds like the truck is in great shape. I don't think you have a problem except fords initial tune. Add some timining to the stock setting, ford was way to conservative in there factory settings. You should be able to safely add 4-6 degrees buy just turning the distributer without causing any problems (just listen for a knock) while gaining power and milage. Even more so if you live at a high altitude.

 

Carbon & residue buildup from incomplete fuel ignitions build up on the piston heads, valve and combustion chamber surfaces and artificially reduces your engines available amount cylinder displacement for compression & at the same time increases compression rate. So it has to work harder to develop less than optimum output. This condition exists at some level in all I.C. engines and the rate it develops varies per vehicle. Causes can be poor function of individual components, short distance city driving or one than insures fast & heavy deposit production is substitution of fuel other than designed for use by that engine. As a rule low compression engines require maximum combustibility properties for fuel used(87 oct.) For complete burn. the more controlled the ignition properties a fuel has the more deposits result from incomplete ignitions. The moral of the story is, unless your truck engine has mods that increases its rate of compression, using higher octane fuels will contribute to a reduction of MPG. A product that helps correct this condition is "SeaFoam",1/3 can into gas tank, 2/3 can poured into brake power booster vac line while engine is idling at norm. oper. temp., and immediately shut off. restart after 15 mins. and continue revving at least until the smoke clears enough to see past the front bumper (If you haven't done this before, you probably think I'm kidding). Also, a performance balanced thermostat like the ones made by Mr. Gasket will reduce the time spent in the over rich warm up cycle before the ECC can enter closed loop function in half & reduces temp. fluctuation during operation. I'll be kicking myself for mentioning this but here goes: Aprox. 2 -3 ozs of Acetone mixed per tank full of gas enhances ability for obtaining more complete ignition of fuel, gradually reduce deposits, reduce emissions and oh yea,increase MPG. Can't be hareware store grade as it has additives to retard evaporation. Gotta go to a beauty supply or commercial chemical distributor. And for something completely different, Tire valve stems rated at specific PSI's. The tips change color when tire pressure falls below optimum pressure so the effort required in monitoring to insure proper tire press. is maintained for max. MPG's, is reduced to an occasional glance at the tires. Pep Boy's carries them.