whenever i prime my fuel pump (running haltech, so the walbro kicks on when the key is at ON for a couple seconds) the pressure shoots up to 50 or so, then as soon as the pump shuts off, the pressure instantly drops down to 5psi or so then slowly down to zero...

does this mean i have a bad check valve or is the pressure supposed to release when the pump shuts off? this also leads to another question..
if this check valve is bad, would that not let my FPR raise the pressure under boost? maybe the extra pressure is just going back into the tank... any input on this would be appreciated.

my fuel setup is as follows: walbro 255 (341 brand new), aeromotive FPR on the return side running ~45psi base pressure, -6 lines, 1600 secondaries, 550 primaries, k2rd secondary rail, stock primary rail.

 

having nearly the EXACT SAME issue. im getting a reading of 65 psi when i check fuel pressure of the pump directly but as soon as i de-energize the pump my pressure will slam down to 5 psi within a minute. also curious if this would be a bad check valve. also jacob are you reading 50 psi when hooking the gauge up directly to the pump or is it teed in the system?>

 

OK you two monkeys.....

FIRST... 45 PSI base is a little retarded... BDC reccomends 38, which is what I run... give an idle pressure of about 28 PSI @ 16 inches of vac with an Aeromotive FPR...

I also have begun to wonder why i use a rising rate fuel pressure regulator.... no need when i have a haltech..... what happened if the vac line comes off and i hit boost.... i'm gonna lean out cause the fuel pressure gonna be too low as the FPR goes back to 38 PSI...

Better just to set it to 40 PSI all the time and adjust the fuel maps accordingley.... know what i mean.... but... i have yet to do this.... so.... i should probably shut up about it...

BUT.......... I have a walbro 255 and the fuel pressure doesn't drop after i cycle the key on.......

If you have something mismatched in the fuel system, the pressure will bleed off as well

Your fuel system..... lets refresh.... OUT from the tank..... IN to the primary rail... THEN to the secondary... THEN to one side of the FPR and the return is out the BOTTOM of the FPR.. right?????? and you have the other side port on the FPR plugged off... right???

I switched to -6an lines... my fuel syste is as such... -6an to Y block.. Y block to primary to right side of FPR.. Y block to secondary to left side of FPR Bottom of FPR to return.

Also.. if you are REAL low on fuel... this can happen, Zkeller found this out... forget exactly WHY but, when we hooked up his areomotive 1000 external pump, it would hold pressure after the motor was shut of untill we put more than a gallon of gas in the tank

Re-check all your fuel lines and make sure that its all kosher.. and then, yes, may be time for a new pump.

 

On a normal RX if you have the pressure gauge TEE'D into the fuel line and turn the key to ON, engine off, with the Fuel Pump Check Connector jumpered, the pressure will go to approx 37-39psi. When you turn the key to off, the pressure should remain in the rail for over ten minutes but will slowly decay over time.

If you put the gauge in the end of the fuel line coming out of the filter (deadending it) and turn the key to ON with the fuel pump check connector jumpered, the pressue should be over 70psi. When you turn the key to off, it should not decay below something like 54pis (see the series five fsm) in five minutes. Personally mine remained at 75 for over five minutes.

I know nothing about waldo pumps.

The series five gives you hints of what to do it the pressue decays too fast (factory pump).

If your tee'd into the rail and the engine is running the pressure should be approx 28-31psi at idle and 37-39 while driving (factory pump). If you turn the engine off, the pressue will rise from 28psi to the 37-39psi figure and then very slowly decay. Slowly to me is over thirty minutes.

 

The leak down happens during running shut down or just key on key off?

I'm running the stock fuel design but with 6an return line from the secondary rail to a Aero FPR with a Walbro as well.

My pressure guage is probably 8 inches after the fuel filter. My pressure will jump instantly to spec and maybe leak down over a half hour.
If from a running state it may show a bit less gas in the lines but it's still high.

I would guess the fuel pump has a back check valve.
My Aeromotive works like a champ and woudl suspect it last compared to my Ebay bought walbro.

 

my pressure will drop immediatly when i turn the key off. this with the car not running obviously because when you are checking the pump pressure output you have the gauge hooked directly to the outlet line from the pump or "deadening" as hailers puts it.

 

Mine shoots to about 35 ish PSI then holds.

Rat

 

There's nothing at all retarded about 45psi. There's no reason why you can't or shouldn't run higher-than-stock fuel pressure as long as the pump can handle it right though the load range and you have the means to fully adjust your fuel map to suit. Raising fuel pressure from 38psi to 45psi will increase injector capacity by ~9% and improve atomisation. Lots of EFI cars run that much pressure stock.

It's funny that you say 45psi is retarded when your RRFPR gives much higher pressures than that under boost.

RRFPR's are really just a band-aid for under-sized injectors. You actually need a fuel controller or standalone to get the best out of them because of the wild changes in fuel pressure. With that you usually end up with overly rich mixtures that are safe but far from ideal.

That same thing would happen with a normal FPR. Your static fuel pressure will still be far too low for safe boosting and a dangerously lean mixture is pretty much guaranteed.

Yep.

 

Bad idea. The higher you boost, the less pressure differential exists with this type of set-up.
If you ran 40 psi of boost with 40 psi of fuel pressure, you would get no fuel into your engine, no matter what injectors. If you ran any higher than 40 psi of boost, you would push air into your fuel system everytime the injector opened instead of injecting fuel.
You have to remember that boost attempts to push the fuel back into the fuel rail. EFI systems tend to have the best atomization around 40-45 psi of referenced boost pressure. Any lower, and atomization suffers, and any higher, and the injected fuel just sprays onto the opposing runner wall.
So... let's say you're running 18 psi of boost on 40 psi abse rail pressure. This is the equivalent of running 22 psi of fuel pressure at WOT on an N/A. Throw in some bigger fuel injectors and a standalone, and see how well it runs like this... with the suffering atomization, the car will make much less power.


The referenced FPR maintains a constant and optimum pressure differential between the fuel rail and the intake system.

 

I think he just meant ditch his rising-rate FPR and go back to a linear-rate one. Bad choice of words perhaps.

 

The series five fsm has you put a gauge on the outlet of the fuel filter and turn on the pump for 10 seconds with the jumper in the fuel pump check connector and pump running. Then remove the jumper and turn the key off.

The pressure after five minutes with the pump off, the pressure should be better than 57psi. If not replace the pump (their words). Stock pump.

That's just looking at the pump pressue with nothing else in system connected to the gauge.

 

it will drop back down as it stills but over at least an hours time. There is a leak somewheres allowing the fuel to escape.

 

wow. great post man...

 

jacobcartmill, man everytime I see your TII I just sit and drool.
I like those rims and that exhaust. One day my TII will have that look.

Chad

 

i sold the wheels and the ballin (and heavy) RB catback made a custom stainless N1 catback and got some FD wheels and painted them bronze.