[Mk2] [Turbo] Big uprated fuel system setup, have a question.

[RyanRs]

I have just finished my fueling upgrade, consisting of :

ATS TFFR
1200's
AN-08 supply
AN-06 return
Aeromotive 13101 FPR
Bosch 044 fitted in the boot,
and a custom tank pickup that i made.

What i need to know is, when i power up the pump (direct to the battery), the Fuel pressure shoots up as it should, set it to 42psi. But as soon as you turn off the pump, the pressure drops back down to zero within about 10 seconds. Is this normal? or should the pressure remain at 42 psi?
I am running a Dead headed rail setup and therefore i should not need to use a Check valve. So therefore i dont know where the pressure could be lost? i have checked for leaks,i turned the pressure up to 60psi momentarily to check for seepage, but there's none.

The other question i have is... should the bosch pump make a continuous constant note while its running at idle? Mine sometimes makes a sort of 'non metallic' grinding noise -it sounds like its air in the pipe.. is this a problem?

thanks

[greeny]

Mine does the same ryan, although im not deadheaded.

Even though you've set your base pressure the pump is still returning fuel to the tank so im assuming the fuel thats pressurised in the rail is allowed to come back through the regulator and draining back down the return.

When mine primes before startup, it drops down to nearly zero before ive started the engine. Never had any problems though.

[RyanRs]

Ok cheers bud. Are you using a check valve on yours? How about the grinding noises it makes? sounds just like when your bleeding the brakes and you get a load of bubbles splurt out of the nipple... if it is air, it wont cause problems will it? im thinking along the lines of the injectors blowing air on occasion?

[greeny]

Ok cheers bud. Are you using a check valve on yours? How about the grinding noises it makes? sounds just like when your bleeding the brakes and you get a load of bubbles splurt out of the nipple... if it is air, it wont cause problems will it? im thinking along the lines of the injectors blowing air on occasion?

Im not running a check valve.

When my pumps first kick in you can hear the fuel rush through the bay/lines rail etc. Never had any problems with it starting this way.

As soon as the engine fires there'l be no air to worry about, i wouldnt worry about air

As for a grinding noise, seeing as your pumps boot mounted i guess its got to suck through the airfrom the pickup if its draining back to the tank, which wont do the pump any good overtime, maybe a good idea to get a check valve just after the pump? As mine are both intank, they are pumping on fuel straight away.

Im a plumber and the circulators/pumps i use can run dry/on air for only a matter of a couple of mins and it can take them out.

I'd get a check valve in there seeing as your pump has a long head before it gets fuel to it.

[larry93]

Sorry to jump in but how do you's manage to keep the fuel cool with running more pumps ?.

Larry

[jimGTS]

Take this info as you wish

when I gave 12v to my pump I also got 42psi of fuel pressure.
Soon as I switched it off it held a good 25psi of fuel pressure for like 10-20mins.
The bgb states fuel pressure does remain in the lines for quite some time, and should be holding 22psi ish for 20mins after switch off.
I've experienced this, tho I basically have an oem setup unlike yourself.

My busted fuel pump only gave 10psi at 12v and the very second I turned it off it went to 0psi.

Not sure how useful that is, but that's what I get some stock setup, with walbro and 850s.

[RyanRs]

Larry, im only using 1 pump. this should remain quite cool as i have positioned it over my BMIC which has 2 x 10" SPALS under it!! Also i am running a Dead headed rail, Basically the fuel circulates from the pump to the reg and back to the tank constantly without going through the rail. this stops the fuel from being heated up in the rail each time it passes through it.

You can also purchase fuel coolers.

Jim. cheers bud, i know the pump is good as its only 2 days old, im just not sure how the pressure can drop tho ???

my rail is dead headded so fuel cannot drain out of it as it would create a vacuum at the blocked end. I would also imagine that once the pump has stopped the FPR would close off the 'Return', locking fuel in the supply line / pump as the pressure will be lower than the 42psi that its set at.

[greeny]

Sorry to jump in but how do you's manage to keep the fuel cool with running more pumps ?.

Larry

My fuel does get rather hot after a few runs you can feel how hot the fuel lines are.

Deadheading the rail does help, as ryan says its not getting the transfered heat from the head through the rail.

I keep meaning to change mine to a deadhead setup.

Fuel coolers work but im not a fan of having fuel in a radiator which is also in the line of fire from debris.

[greeny]

my rail is dead headded so fuel cannot drain out of it as it would create a vacuum at the blocked end. I would also imagine that once the pump has stopped the FPR would close off the 'Return', locking fuel in the supply line / pump as the pressure will be lower than the 42psi that its set at.

Not sure whether the return out the regulator shuts off, but if your return is in free air in the tank when you shut it off, air will be able to go up the return and drain the fuel into the tank. With you saying your pump runs dry for a couple of secs on priming then maybe it is gettin its air from the return letting it drop back to the tank?

Maybe fill the tank to the brim and see if the same happens?

[RyanRs]

i see what your saying, thing is tho i made the return tube only about 1/2 " shorter than the pickup. iirc the pickup was 11" -the same length as from the bottom of the stock pump to the top of the tank.

the other thing that could cause this is an air leak at the bulkhead hose fitting, but if theres one part that i know is sealed tight, its that!!

heres the pickup..



Now, heres a quick pbrush sketch i done of how i think a FPR works:-


Is this correct? if so then i can assume that any pressure thats bleeding off will be returning from the rail and backward through the fuel pump as the Return valve will be shut solid...?

[Jimbob]

Not sure the drawing is quite right TBH. Thats not how it looks internally anyway.

I think the normal convention is for manifold pressure to assist in closing the regulator (raising pressure), as well as how much tension you put on the spring by winding down the adjustment. Yoiu've drawn yours being pulled up into the seat.

As you have drawn it the rail is always pressurised and the return only opens when you overcome the regulator setting.

Where do you read fuel pressure? if its on the rail it will die away as you have yours set-up. With the conventional set-up (like i've got) the pressure remains trapped in the rail and very slowly leaks away through the clearance in the pump and probably the fpr.

I'm not quite sure what you mean about a check valve (I know what a check valve is). If you mean directly after and inline with the pump i dont see much benefit as the fuel pump is a PD pump so will by design keep fluid pretty well trapped.

[RyanRs]

Yep i see a few errors on that deisgn now i have thought about it a bit more. I was using the principle of a preloaded spring pulling the return valve 'Up, and say the pre-load is set to 45 psi, then the fuel passing into the rail would have to exceed 45psi to overcome the pressure of the spring and then open the return valve, kinda like an external wastegate.

But my idea suggests that the pre-load will be Increased when the screw is wound Out as opposed to In like they are. Also the diaphragm at the top of the drawing would not work.

But anyhow, the gauge is fitted to the port on the front of the FPR its self. I have been told by a few people now that the pressure will bleed off quite fast with big pumps. However, i think i may have a slight leak on the fitting at the pump end of the supply line, i had left some electrical tape around the end of the hose at the fitting and i have noticed its gone all soft/soggy and theres a sticky residue running down the bottom of the hose. i imagine that this could poss be the cause of my problem.

Jim, what pump / FPR and config are you running?

[Jimbob]

Walbro in tank, Sard FPR, Wolfkatz rail, Seimens 872cc top feed injectors. Got plenty of spare fuel.

I'm slightly struggling with the BIG fuel pump passing fuel back. I'm not overly familiar with them............but a normal PD pump (I think fuel pumps are sliding vane type) the fluid is forced out of a pumping chamber or cylinder by a moving pumping element. The efficieny of that pump relies upon the clearance being good. I would expect the pressure to die away quite quickly from full pressure but to hold a lower pressure for a good while.

From memory my pressure will drop into the 20's quickly then slowly decay to around 10psi but stay there for sometime. I wouldn't be overly worried if it dropped more quickly, I don't think. Instantly from full to zero suggests there may be a path for the pressure to escape? So long as your pump makes good pressure I would concentrate more on your plumbing

Why not just put your FPR on the rail then the return to the tank?