hi, this is my 1st post but ive been lurking for a while, thought you guys might be able to give me some tips... I have a 01 dodge 24v, edge tuner, intake, exhaust and fas 95gh lift pump. My fuel pressure reading on the edge moniter is jumping around, at idle it moves from 15-19, normal driving it will move from 12-18, if i really get on the throttle on a hill. on level 5, it drops to 9psi... I ran clear line between tank and pump and pump and filter and there were NO air bubbles. i hooked up a mechanical gauge and ran it at idle and it was still fluctuating. I plan on adding some 100hp injectors soon so i want to get this figured out first...

thanks in advance

 

Might want to change the overflow valve. It is the banjo bolt in the VP44 for your return line. They are set to open 18psi, but may be opening differently.

 

i have a fass 150 on our 01 truck and it does around the same thing but it dosnt drop less then 12psi with 150hp injectors, i'd say change the filters and you should be fine

 

forgot to say, brand new vp44 and overflow valve, replaced filter recently as well..

 

Hmm, that's a little different then. My FASS 150 will have 23-24 at idle, and 21-22 while driving, and 19-20 at WOT.

 

Any news?

 

So, ran it out of a bucket, no change, pulled fass pump apart to check for wear/debries... all good, i streached out the relive spring a bit before i put it together, got my fuel pressure up to 21psi but still fluctuating. then I ran an 18" hydraulic hose between the pump port and sensor... now pressure is steady 20-21 at idle, if i really crank on it i can get it down to 14... so im pretty happy with that, see what happens when i install 100hp injectors

im a hd mechanic so im used to the big cummins isx/ism etc. on those trucks the lift pump comes on with the key switch for 2 min then shuts off... my fass does not turn on with key on, just comes on when truck is running, doesent seem right to me? when i get in the truck in the morning my fuel press is at 4psi, as soon as i start cranking it builds up to spec...on my race car i have my fuel pump wired to a switch so its always on... anyone do that with a fass or is my issue normal? thanks again

 

How do you have you FASS wired up?

I have an aftermarket pump (AirDog) wired up to the stock fuel pump leads on the side of the engine block... When I turn my key on, it runs for maybe a sec or two. If I bump the starter it'll run for 25-30 sec.



As far as your pulsation issue goes, the VP44 produces spikes in the pressure. It's called the "water hammer" effect. You can kinda feel it if you have two sinks next to each other in the bathroom. Turn on the water on both... Now turn the water on and off on only one sink and watch what happens to the water in the other sink that's just constantly running.

The hose you added acts as a shock absorber. You can also get a Pressure snubber. It's just a fitting with a little grid in it that also breaks up the pulses.

After a while, those pulses might break an electronic sensor, so a snubber or a length of hose is a good idea to have.

 

Pump should come on (bump) with wait to start. You will hear it.

 

thanks for the help guys