I bought a 94 f150 4x4 5.0L in decent shape (for Minnesota) for $700... It's been sitting for over a year... It's been running like crap, and stumbling, and been having to basically mash the throttle to do 50 up a small hill...
The fuel pressure at the rail is 30 PSI.. But it's the same on both tanks (dual tanks). It shouldn't be the fuel pumps in the tanks, why would it act identically on both pumps.. I know they share the same filter....

I know running injectors at a lower pressure is like leaning out an engine, and would cause me to push the throttle more to get moving.. But, why would that cause such bad fuel mileage? I'm talking like 6 MPG...

Any ideas would be awesome... I'm mechanically inclined and have access to a shop, so I don't mind doing the work. I just don't wanna spend lots of money on this truck...

Thanks

 

How did you come up with the 30psi pressure reading?
Was the engine running at idle or did you just turn the key on and off a few times?

What codes are you getting if any?

 

I used the Cornwell Fuel Injection test kit. I plugged it into the valve on the fuel rail, started the truck and read the pressure while at idle, when I rev'd the engine, it actually dropped to 28 psi, the up to 32 psi and settled at 30 psi again. Turned off the engine, swapped fuel tanks, started the truck again and the same situation...

The check engine light is on and I don't what all codes are on. The guy I just bought it from said the light was on because of the EGR valve. I haven't checked anything yet on the EGR...

 

Don't forget the pressure regulator. It should be at the back, on the drivers side (I think). Pull off the vacuum hose. If fuel comes out, you need a new one. There's a few other things to check with the regulator, I just can't remember them. And a new filter is cheap, and never did any harm. Replace it.
-Mike

 

You really need to pull the codes, you may be barking up the wrong tree thinking fuel.

 

Fuel filters go bad a lot less than people think. Not to mention, if it is clogging, you would start to notice it beginning at wide open throttle, gradually getting worse performance at lower and lower throttle positions.

But, today's gas is very clean, and gas tanks tend to stay pretty clean inside.

Jason

 

Already checked the regulator and no fuel smell or fuel in the vacuum line... I'm gonna pull the codes this weekend when I have time after work...

 

Redo the test. This time, remove the vacuum line from the FPR (plug the vacuum line) and see what the fuel pressure is with the engine running. With the vacuum line off the FPR, you should see ~40-42 psi at the rail. 30psi at idle with the FPR vacuum line in place is normal.

You also need to run the codes. That CEL is a huge clue as to what the actual source of the problem is.