Hey guys.
my fuel pressure disapears after priming. it goes upto 40psi then drop within 5-10sec back to zero. Im running a walbro intank 1680x720cc inj and a malpassi reg. Ive got a gauge hooked up inline after the Haltech E6X primes the system it drops off again.
I pulled my reg apart to inspect for dust/grit and it was clean. I have no leaks coming from hoses. The 1680 sec inj are brand new and un-used and the primarys were cleaned and tested no more than 1200kms ago ( abeit 3 years as ive been travelling overseas )
I would take the primarys into get checked now but the closest place around here that can check is an hour away.
I might rig up some fuel hose directly from the pump to a injector and see what happens??
I swaped out my walbro back to the stock pump for a test after doing some research to see if the saftey valve was malfunctioning and the stock TII pump is holding pressure for a little longer but it drops to 15 instantly then bleeds to 5 over 20 secs and then to zero.
Whats up with this? anyone got any clues??

 

Leaky injectors?

 

sometimes the one way valve in the fuel pump has died.

 

Simple as this. Put the fuel gauge in the end of the line that comes out of the fuel filter. Turn your series five car switch to ON, then OFF. Observe the pressure. If it still decays at the same rate, then it's the pumps checkvalve.

But really, who cares if the pressure drops?????? Anytime you HOLD the key to START the pump is running and anytime the engine actually starts, the pump is running. So what's the big deal??? No big deal at all. As long as the fuel pressure in the rail is right for a given condition other than what you describe.

Series four have no PRIME bull built into them. You turn the key to ON and the pump does not run at all. Turn the key to Start and the rail is pressurized in less than two seconds easily even if it was bone dry prior to Start.

As for leaking injectors........that's why you have a fuel pump check connector and have the ability to zip tie fuel injectors to fuel rails that are unbolted (so you can see the bottom of the injectors for fuel leakage when the rail is pressurized.

 

Good Idea Hailers!! I like your style. Back to the garage

 

There is probably nothing wrong, unless you are losing fuel pressure under boost. This is common with aftermarket fuel pressure regulators. My Aeromotive has been doing this for years.

 

yea the pump was fine, i checked both. then i plumbed the fuel line so it bypassed the fuel rails and went directly to the reg with the gauge inline and it dropped off almost as quick. after putting it back together, noticed a o ring was leaking, so replaced that on a primary inj and it held a bit more pressure.

 

On my stock cars the fuel pressure will stay in a high reading for over thirty minutes or more. The pressure will decay but on the whole stay high for quite a period of time.

LIke they say above, you should be a bit concerned if the pressure won't stay where it should be when boosting etc. I shoulda said something about that earlier.

 

The one way valve in my fuel pump is shot. Hasn't really caused me any issue though except during hot start. I have to bump the ignition to get the pump running, and once it fills the lines, it starts right up.

 

yea i sometimes rig up a oil pressure sensor into my regulator and have it coming thru to the cabin on my gauge and have never had any probs, its a rising rate reg as well, just to make sure theres always enough gas! one motor blowing up due to lean conditions was enough for me.
thanks guys

 

so did the o-ring fix it, because another way to test the regulator is to pinch off the return line and see if it holds pressure then. If it does, than the FPR is leaking if it doesn't than it is the injectors or the fuel pump.