96fd3s

Hey guys, not sure if its an issue or not, but I was trying to pressure test my new fuel system and noticed the fuel pressure drops pretty quickly after priming.

The car is not yet at a stage where I can try to start it, but my ECU primes the fuel pump for a couple of seconds when you turn the key to on. So iv been using that to pressure test it / check for leaks.

I didn't detect any leaks, but the pressure drops steadily after the fuel pump priming stops.

I have a couple of theories on this;

A. the fuelab mini FPR perhaps does not maintain pressure after shut off or after fuel pump stops?

B. my vent line is not currently hooked up to anything. Will this make it not hold pressure? I could cap it off to see if it holds pressure but thought id just ask because im sure someone already knows!

Maybe even both A and B?
cheers

EDIT: fuel pump is a walbro 400lph. included this as I read some fuel pumps have a check valve to keep pressure after key off.

96fd3s

found this on the fuelab website;

"Our regulators are a metal to metal seat, which will never be a 100% seal when the system is turned off. It is completely normal for the system to bleed down after it is shut off. If there’s no check valve in the system, the bleed down will happen even quicker. It’s also possible that there is debris stuck in the seat area, which is holding the diaphragm assembly open. Assuming there’s no debris or damage to the seat (easy to spot because the black anodizing would be worn away), what you are experiencing is considered normal operation for a system after it has been shut down."

Ok so its normal for it to bleed down. That's cool. It drops quite quickly though. Maybe 5 or 10 seconds for the pressure to bleed out.

Stupid question.. but, does anyone know if, in theory, I have a check valve in the system? Does the walbro 400 have one?
Fuel lines in the rear of the car are stock. Firewall forward i have replaced.

Im thinking its a combination of the FPR not holding pressure after shut down (which is normal), and the walbro 400 perhaps not having a built in check-valve, where the stock fuel pump perhaps did?

EDIT; i have messaged both "ti automotive" and "walbro" asking if the 400lph pump has a built on check valve or not. Hopefully they come back to me. Would still like to hear from anyone else though! cheers

IRPerformance

iTrader: (41)

The check valve is in most pumps to prevent reversion pulses and all of the fuel from draining from the lines after shut down so that you don't have to crank excessively the next time you start the car. Some pumps like the Bosch 044 come with an application-specific check valve that is difficult to adapt to the fd, so most people remove it causing the above problem. You can get small inline check valves to remedy the problem and there are even -an ones that will screw directly to the pump. Walbro and Denso pumps do have check valves. The bleed down you are experiencing is normal because the check valve is on the pump on the feed side, not on the return after the regulator.

96fd3s

awesome, thank you good sir!