sixty7

ive read many threads, done some footwork, and im still baffled. just picked up a 92 f150, 180,000 mi, 2wd shortbed ex-cab, 4.9 5 spd. truck runs great, good power, no stumbles, no trouble codes, i checked egr and is functional, and replaced the o2 sensor because it was cheap insurance. truck has good 275/35 tires, 3.55 rear, and no matter how i drive, im consistantly getting 10-11 mpg. my commute is about 25 miles one way, 20 of which are highway, and i cruise at 60-65. I dont expect 20 mpg, but i at least would think it should pull an easy 15mpg. it fires right up, never stumbles, and never gives any signs of problems. Im going to test cyl pressure next, check timing, and check for bad stuck brakes and such, but does anybody have any other ideas as to why shes so thirsty?? any help is greatly appreciated

David Young

I get 17 mpg around town with my 91 4x4 4.9 5 speed but i have factory size tires and a 3.08 gear ratio. Maybe try cleaning your throttle body, it might be gummed up.

David Young

After thing about it, i don't think its a dirty throttle body. Do a full tune up with new wires, distributor cap and Motorcraft sparkplugs. Change the fuel filter too. Your on the right track checking your timing, I bet its off a little, that would cause bad gas mileage. It could be so many things

Christopher1990

I would pull codes. A lot of sensors can make you suck up gas for no reason. MAF, TPS, ect. Check and clean out your Idle Control Valve it's super easy and fast. Vacuum leaks is a big one. Do full tune up including air filter. I'd do Fuel filter it's cheap and easy.

24willyboy

David is right, it could be a million different things. My 4.9 was running smooth as could be and got about the same mileage, with mine it was because the PO had stripped out the threads in the engine block for a spark plug, and simply glued it in with loc-tite, and when the stuff burnt through, the spark plug came loose, and started shaking until it shattered the ceramic top of the plug and started having a misfire (which, in an inline 6, is harder to detect sometimes than you'd think, especially with how smooth they are and when the CEL bulb was burnt out without you realizing it lol). I only noticed it when I was detailing under the engine bay and when I started it up to dry the gunk off of the engine I noticed that plug ticking like crazy, and when I went to pull the plug wire off the whole plug came with it, and little pieces of ceramic went everywhere. I replaced all the plug wires and plugs, and it gets about 15 mpg now. A 4.9 doesn't get great gas mileage at all, and little small problems can bring them even further down a LONG way. A good tune up (plugs, plug wires, oil change, fuel treatment, check timing, etc...) should do it some good if anything. See if you can pull some codes too, sometimes that'll tell you the exact problem, sometimes it doesn't but it's always worth a shot! Hope I could help!

coachk64

I had a 91 F150 with the 4.9L and when I first got it it had 30" tires on it, and I was getting about 12-13 MPG. When I switched it back to OEM recommended tires (215-75 I think) my mileage immediately improved to about 16-17 MPG, with a very noticeable difference in highway power. With the oversized tires, pulling a trailer on a hilly highway, I was spending more time in third gear than in fifth.