Hi, I'm new to this forum. Looks pretty tight and lots of good answers to peoples questions.
I bought a 1991 f150 extended cab with 6 cylinder inline 4.9 motorwith 140 K miles . The fellow i bought it from swears he was getting around 14 in town and 19 on the highway. I'm getting a good soild 9 per gallon around town. I've done the following:
>replaced battery wires.
>changed air and crankcase filter.
>installed new muffler(old one was mostly not there. The whole back of it was missing"
>replaced fuel pump in mid tank

Aside from the above i tightened 5 out of 6 of the sparkplugs. Some where really loose.
I notice it idles high.
Also it seems to run way cool.
My next step is going to be to replace the thermostat and the sending unit.
I havn't run any codes on it yet.
Thanks for any help
Rich

 

Replace them and do a tune up. Replace the cap, rotor and wires as well.
Pull codes.
Don't rely on the stock gauge for correct measurements of temp, oil pressure and voltage.
Thermostat probably needs it anyway. And sending unit is easy enough to do. However, I would also add a real temp gauge.
See above.

 

as it has high idle do you hear any hissing or notice a vac leak, this could make the high idle wich result in low mileage

 

what trans do u have? and how do u drive i get 16 city in mine without over drive but if i beat it i only get 12 or so

 

Hopefully he got his issue resolved...it has only been two and a half years.

 

my mistake, was looking for info about my thermostat an since my mileage is getting worse i took a look at this thread and forgot the date

 

It has been a while ......Part of my bad gas mileage is because i have dual tanks . The front tank recirculates into the rear. In calculating the mpg i didn't know gas was being sent to the rear......Duh.... I still sense it's a gas hog.

why would the front tank dump into the rear....anyway!

 

Its a common problem and there was a recall to fix it.
Easy solution:
Fill both tanks
Run on the rear till near empty
Switch to the front
Run on the front till near empty
Switch to the rear
Re-fill and repeat

 

These captions explain how the '90-96 fuel pump works, and why it can transfer fuel between tanks. There's also a link to the recall.