Hey I'm new to posting to the forums but here goes nothing. I recently changed the fuel pump on my 02 F-150 (4.6 V8) with much guidance from these forums. The truck was getting to where it would not start right away. It would crank and crank but wouldn't fire. I replaced the pump and it fixed that issue. Now the fuel mileage has decreased significantly (4-5 mpg). Do I need to have the computer reset or any other ideas on what could cause this?

Thanks in advance

 

It should not effect the computer. Are you absolutely sure it is not leaking someplace? Perhaps the sending unit on the new pump is not accurate?

 

When I changed mine I was warned that the sending unit was redesigned so it was more accurate in mid and low range. I used to be able to top off the tank and drive 50 miles before gage moved now it starts moving after 20. Might this be what you are seeing? My actual checked mileage has not changed.

 

I am pretty certain there are no leaks. I cannot smell gas when driving and I felt around the lines with the truck running and I do not feel anything. I only removed 2 lines in the whole process. One line was a return line and one was a pressure line.

 

I thought about the sending unit being calibrated differently. I saw the exact same difference with the gauge moving faster after a fill up. However when the fuel light kicks on the tank is pretty much empty (based off fill up capacity). I used to get 360-370 miles to a tank in the city and that fell off to right at 300.

 

What are you fuel pressures?
Did you check for pending codes?

 

I do not have a way of testing the pressures, unfortunately. The check engine light has never come on. I took the truck to a mechanic prior to changing the pump and his code reader did not come up with anything. Could I pull one of the spark plugs and made a judgement there?

 

Hard to tell looking at plugs if there is no black exhaust smoke.
High fuel pressure can cause a rich condition.

Since the fuel mileage dropped right after installing a new fuel pump,high
pressure could be suspect.

It only takes a shop a few minutes to check it to confirm
the pressures are within spec.

While I was there, I would get it scanned for pending codes as well that
are stored but not yet lighting the CEL.

Good luck
keep us posted

 

Thanks for the advice. I might try that. If there was fuel leaking at the return line on the pump would I be able to feel/smell it with the truck at idle (ie sitting in the driveway)? When I changed the pump the plastic securing mechanism on one of the lines was partially broke. I think it will hold but that's the only source for a leak I can find.

 

kevin, if it was leaking a gallon external you would see that.. I think what vapor is saying is if the truck was suppose to have 30 psi pushing thru an injector and you put a pump that has 50 psi, it might push more fuel thru that injector with each pulse.

 

you should have a pressure regulator on the firewall that dumps back to the tank when the pressure is too high. It does not seem like a new pump would cause the excess usage.

 

I was thinking maybe the old pump was weak with a poor regulator,
install a new pump with the same regulator maybe =high pressure?
I think the regulator should be by #7 cylinder on this generation Steve?

 

That needs to be repaired
Gasoline is extremely flammable

 

I think your right vapor....... seems like the regulator is on the drivers side, maybe in front of the brake booster... should set on the fuel line and have a vacuum hose to it ?

 

yep....I know it's always in the way when changing #7plug/coil