Truck has some type of performance muffler that I am going to change out for a stock unit, I know it needs an alignment, it has 120,000 miles on it, so it could probably use a stronger ignition system. It needs a valve cover gasket but I don't think it will effect mileage. I replaced the K&N filter with a stock unit because I have never had a performance filter that gave better mileage than stock. I run 40PSI front and 38PSI rear on 31" BFG Long Trail T/As. My driving is mostly city with a little highway. I know 300s should get better mileage. I'd like to know which of the factors above is the most likely culprit

 

Check fuel presure and pull the codes, that's the best way to start to diagnose your problem.

 

I just got back from a 400 mile trip in my 95 F150 4.9 E4OD w/ 3.31 gears and got 17.75 mpg running 75-80 w/ the A/C on. You should be getting better mileage than that.

 

What size tires were stock for that truck? When I corrected the speedo my mileage jumped 3-4 mph

 

hell my diesel gets better than that

 

Original tire size is 235/75/15, there are 31/10.5/15s on it now. I know I should be getting better mileage than that. Even without driving on the highway at all, I should be getting better mileage than that.

 

my 300 gets around 11-12...with 210000 miles and a leaky head gasket among other things...ill let you know when i rebuild it haha

 

Between the tire size and whatever gearing you are running may be a big part of it.
The gearing may be loading the motor up too much and not letting it stay in the power range it was intended. Like someone else said early, if you are not correcting for the difference in actual mileage from the speedo, then that will definitely change things.

A good old tune up will usually help any engine, unless you have recently done this to it. Just some ideas. Good luck.


P.S. My truck gets between 17.5 and 19 MPG depending on how big of a hurry I am in. It has 275-60-15 tires on it. So when I am just cruising along, it gets pretty decent for a truck, BUT when I get in a hurry, it likes to drink the gas.

 

Those are the same tire sizes I had, when you update the speedo constant in the speedometer that will change the mileage by 3-4 at least.

Look here: https://www.ford-trucks.com/article/...ND_BRONCO.html

That is what I did. Do that it's easy.

 

I think the first thing I'm going to do is a Tune Up and Alignment, next will be the exhaust followed by going back to the original tire size. If that still doesn't fix it... Well, I'll see to that if it happens.

 

WHY not do the easy things first.. like pull the codes... BEFORE you spend any money. If you find a problem then you can address it directly instead of just shooting randomly in the dark.

 

i will add:

 

That'l be included in the tune up.

 

And just so you know it's not hard and requires no special tools. Find the EEC test harness on the drivers side inner fender and jumper the STI and Sig-Rtn lines with a piece of wire or paperclip. Turn the key to run and count the flashes on the check engine light. You can cycle the key and count them as many times as needed to get it all right. Post up the results you get here and we'll help sort it out. Your truck should have 3 digit codes with each digit seperated by a short pause and individual codes seperated by longer pauses.

 

Damn that sucks. My 95 F150 4.9 mt 2wd dances around 20mpg. I'll hit 21 21.5 every now and then but that's about it. Truck has 166k bone stock. Did a tune up a cple months ago but it didn't really change anything. Don't know what your driving style is like but I drive like an old man, it helps.