I have a 1995 with a 5.8. I just put a new fuel pump in it and now I'm getting almost half the mpg's I was getting before. Why would this happen?

 

Wow half? What exactly? Could be fuel pressure regulator . It may not be used to the added pressure.

 

I wonder if the computer could have been compensating for low pressure and is still doing it. I don't even know if that's possible, but maybe unhooking the battery for 1/2 hr will let it reset ?

 

I was questioning the fuel pressure regulator before. I don't have exact numbers but I used to fuel up once every 3-4 weeks (I live just a few blocks from work) and now it only lasts about 2 weeks. I'll try unhooking the battery and see what happens.

 

Dual tanks? One doesn't work? I'll bet it's crossfilling.