Fuel pressure questions

[BillRod]

Hi All

95 F150, Big six, 5spd, extended cab, dual gas tanks.

Few weeks ago I noticed an intermittent hesitation when driving using the rear tank.
Switched to the front tank all seemed ok so I figured it was the pump.
This week I noticed a similar hesitation using the front tank too.
I put my pressure gauge on the fuel rail and ran it out the back of the hood to watch it while driving.

Idle is 50psi, pressure raises to 60 psi under full throttle.
psi seems to be in relation to the amount of pedal I use, no pedal 50, 1/2 pedal ~54, full pedal ~58.
I guess that is how it should be?

Issue/Question: The needle jitters, it is never calm as one would think.
At idle it jitters maybe a pound or so. Half or full throttle the jitters varies a lot, either a little or as much as 8-10 psi. The only time the needle does not jitter is when I pull my foot of the gas and compression braking slows the truck.
Also I did feel the intermittent hesitations that started all this and that seemed to be when the need jitter was 8-10psi.

Should I pull the bed and replace the pumps? Is the extreme psi jittering enough to cause not enough fuel to let the engine run right?

History of the pumps: Bought the truck in 07 with original OEM pumps. Rear tank went out shortly after buying the truck, ignored it and used the front tank until that pump went out in December of 09. Replaced both original OEM pumps with AutoZone pumps in Dec 09. When I had the pressure gauge on the original OEM front pump it never jittered, it was nice and calm.

Any thoughts on any of this?

Thanks
Bill

 

[shane96ranger]

Are those numbers with the vacuum line removed from the regulator (and vac plugged off)?

 

[BillRod]

That is simply with the fuel pressure gauge on the fuel rail.
Same way I did it back in December '09 when I hooked it up to diagnose the OEM pump. Back then the needle was smooth. it did not jitter as it is now.
Sometimes the needle is bouncing back and forth so fast it's almost hard to see.

One thing that I do not notice now is the pressure dipping low during the hesitation as it did in 09. Back then it was very easy to see that the pumps were not pushing enough pressure during the hesitations.

Since it is both pumps I was wondering if it was either the Autozone imported pumps or something that controls them?

 

[shane96ranger]

Without being 100% familiar with the F-150's system, it would be my guess that it is something both pumps share in common. Do they share a common filter? I would start here if so.

 

[shane96ranger]

I was recently experiencing a similar issue with goofy readings. I started at the filter and found the filter media had broken off inside. Here's a poor quality video to show what I mean:



After this, I got really weak readings still, but not as erratic. I wound up replacing the pump with a US made Carter pump which cleared up the weak reading.

EDIT: The Fram filter I took out said Made in China. I can only find a US made filter for mine at the dealer.