fass fuel pump went down to 5 psi now works fine

[VHolloway]

when you bump the starter it's 20psi.
at idle 17-15 psi but the longer you drive the more it creeps down
then the next day it's ok
and it starts all over
we have changed the prefilter the filter this is the pump only fass
we have two fuel pressure gauges

[VHolloway]

It seems when it's real hot out it drops pressure the more you drive the more
it drops
not good

[Jefff929]

How much fuel do you have in your tank?

Is the reduction in pressure affected by ambient temperature?

[VHolloway]

we never let it go under half a tank
thanks

[Diesel-Dan]

Originally Posted by VHolloway

when you bump the starter it's 20psi.
at idle 17-15 psi but the longer you drive the more it creeps down
then the next day it's ok
and it starts all over
we have changed the prefilter the filter this is the pump only fass
we have two fuel pressure gauges

Well ambiant temp will have some to do with fuel pressure. Mine moves around about 2 PSI depending on how hot and cold it is.

As for the dropping and such, Gauges. What are they? Mechanical? Electric? Isolators?

When you changed the Pre-strainer on the HPFP, what number did you use? If you used a filter (like 10um), this could cause issue as well. Make sure its a NAPA 3270 strainer.

20 PSI seems a big high really....we usally see them at 16-18 on the bench here.

Might try pulling fuel out of a bucket as well. See if the pressure comes up any.

Whats the lowest it gets?

[VHolloway]

one gauge is a dakota digital the other is a test gauge from genos
but it went down to 5 psi
man my hart skipped a beat
we parked it the next day it was up to 15 psi
but the longer you drive the lower it goes

[MountainMan1]

How old is the pump...perhaps the bearings are going out. I had that happen to my FASS after about 6 months.

[VHolloway]

do all the lift pumps out there have this problem
may just give up and get a 12 valve truck

[VHolloway]

I have two or three 3270 pre filter from napa i keep in my truck
some times napa runs out so i keep extras on hand
yes I just put one in
changed the big fuel filter as well

[VHolloway]

we went to the gun store and it went down to 8 psi and we where not even
on it hard I just don't get it!

[Jefff929]

Originally Posted by VHolloway

do all the lift pumps out there have this problem
may just give up and get a 12 valve truck

I have had my full-meal-deal FASS for about 3-4 years. It is the old style, supposed to be noisy but I can't hear it, and have never had a glitch yet. I know of a couple of guys who put a cam in with an extra lobe and use a 12v pump, that is another option. Most who run FASS, AirDog, Racor, Walbro or mitsuwhatever pumps are happy with whatever choice they make.

Personally, I'd look for restrictions or air getting in your lines. You may have a collapsed or collapsing line. I have seen lines telescope inside of themselves creating a restriction. Your situation is unacceptable and there has to be an answer. Do like Dan said and see what happens.

[Diesel-Dan]

Come monday, call your dealer with your HPFP SN and we will see what we can do.......the only thing in the pump that could be causing this is debris in the check ball seat.

[VHolloway]

can junk get in even if we have the prefilter
it was working so good to
would it have happend if I would have got the high output pump

[BMote]

I have had similar issues on more than one occasion. Always turns out to be an isolator problem. Now, I just recharge isolator with antifreeze mix about every 4 months and have had no problems for a year or more. Just my 25 cents worth.

[VHolloway]

I have just the pump
I"M LOST isolator
help me out here i don't get it

we had the truck out to the store at first 18 psi idle
by the time we got home we had 8 at idle it slowly went down hill
I just don"t get