Ok so I have a 93 with the 3.9 I've got a lift on it with 31s (yes I realize going back to stock would help but I refuse) 3in Flo master super 40 series exhaust with magna flow hi flow cat. I have a v8 tb on it (that helped) new plenum gasket I'm about to do the e fan swap. New o2 sensor and iac valve sensor relatively new egr gasket.. Yet I'm olny getting 9.5 mpg yea that's with compensation for the tires. Oh and I have a tight budget and this is my only vehicle so it can't be out of commission for more than a day and I have emissions.

 

my 2001 dak V6 3.9 auto trans was getting 8-9 MPG. course i drive hard. i had a 4.1 gear put in. made my trany go into O.D. at 35 MPH with no other changes. my MPG went to 11-12. BUT i drive ONLY in town, no 50 MPH. an other wild idea try Marvel mystery oil in the gas, 4 oz in 10 gal. some people get better MPG, not a lot but some, but NOT all the time.

 

I have a manual transmission and idk about the oil in gas

 

well you got something seriously wrong somewere.. unfortunately cant help were...

You might cry here.. but I have very little mods to engine on my 92 extended cab.. 318 but highway with 33's and a home built winch bumper(250lbs~) I get roughly 25~ highway and 18~ town driving like a old man... easy on throttle.. but when in mud I watch the gas gauge move..LOL

now tho I change air filter every oil change cause its only 5 bucks..
I use mobile one synthetic
modified airfilter with dual intakes(just takes air from under hood)
all difff's and trannny were changed out this summer for synthetic ..
if antifreeze was made synthetic it would be too but I got Ford Gold Antifreeze in er.
has 3:55 gearing ... no bottom end unless in 4low ..LOL reving highway speeds 1800~ rpms

 

I wish.. Maybe once its warming out i can do bigger things cuz I have a motorcycle that I can ride but its too cold and rainy in Washington to ride throughout the winter.

 

The usual things I do to improve any vehicle, change plugs, wires, cap, rotor, clean, replace or rebuild the injectors. Check for vacuum leaks. Make sure all moving parts are greased and in good working order. It can add 20-30 miles to a tank full.

 

I just did a new tune up

 

Everything you've done has contributed to you crappy mileage. Lifting the the suspension gets it right up there in the air to increase air resistance. The big tires have more air and rolling resistance and require more hp to get going. Your Flowmaster exhaust, hi-flo cat, and V8 throttle body flow more air/exhaust, but that requires more fuel (the pcm compensates the keep the air/fuel mix correct.)

You can tune it up to your hearts content, and run the tires with 90 psi, and you probably won't see any improvement. Your manly, manly truck is just gonna be a gas hog.

I don't mean to be grumpy, but there really is no free lunch.

 

Actually there is a synthetic coolant. I'm going to change over to this stuff in November. Benefits--never needs changing again, doesn't permit corrosion, much larger range of protection, non toxic, and not bad for the environment. Negatives-price (really spendy!) and totally not compatible with water or antifreeze.