Hello all,

Last month, I replaced both of my fuel tanks, as well as both fuel pumps in my 1991 F150 (6cyl). I also changed the fuel filter when I changed the front tank (about 2 weeks prior to changing the rear tank)

I have noticed that when I switch to the rear tank, the engine seems to hesitate and stumble on acceleration, and kind of acts "constipated" when at speed (55+mph). The feeling I have - is that it's probably low on fuel pressure and not getting enough gas to the engine. Possible? Probable?

I do not have a fuel pressure gauge, yet, to check the pressure at the engine - but may pick one up next week. Any other known issues for me to explore? With the pump being brand new - I am hoping that it IS providing adequate pressure. Is there a juncture somewhere prior to the fuel filter for me to check for debris in the line? (the old tanks were full of rust - and thus the reason for the change of tanks/pumps)

Thanks,
Rex S.

 

Buy the f/p gauge. My $60 one has saved me (and the family) many, many hundreds of dollars in unnecessary "try this" repairs.

 

Back a few years we changed both pumps on our 95 6cyl. Rear pump died after about 10 months, upon replacement realized we had kinked the fuel line. Not sure if a gauge would have picked it up, but the flow had to have been diminished. You're probably a better mechanic than I am but worth a look anyway.

 

I'll double check my electrical connections tomorrow evening, and follow the lines up to the filter to make sure they look okay.

I first experienced this when I ran the front tank almost completely empty in an attempt to see how far a 19 gallon tank would get me. Once I switched over to the rear tank - it ran okay for a bit - but then started the hesitation & stumbling on acceleration. Maybe I'll fill the front tank up and see if that helps. If so - I'll simply use the rear tank first after filling up both tanks.

If wiring harness check & double check of the lines does not fix it - then I'll spring for the fuel pressure gauge...

 

I finally made time to borrow a fuel pressure gauge from AutoZone.
Pressures were read with engine running, at idle, as well as gunning the throttle occasionally.

Front tank: A consistent 48 psi under all conditions listed above
Rear tank: Needle wobbles FAST between 28-36 psi.

I suppose it's time to contact the company I bought them from and let them know my readings... unless anyone has a suggestion to try first. (would a line with crud in it have a fluctuating pressure?)

When the rear tank is selected - if I'm at a consistent speed - it seems fine. but if I need to press the throttle (i.e. to accelerate from a stop or to speed up on the highway) - then that's when the stumble and hesitation/constipation kicks in.

Rex S.

 

I think your truck wants 45 to 60 psi, with 60 being preferred and under 45 not being enough to run the truck properly. So fuel pressure seems to be the problem.
And yes, a line with crud in it could do that. (might not be the pump's fault)