Fuel pressure drops after a while

[djsteffen86]

Hi all,

I don't know if i'm posting in the right forum, but i'll give it a try

My problem is, that my fuel pressure drops, after the car have been idling or driving..

My fuel system setup is a 044 fuel pump and a adjustable fuel pressure regulator with a pressure gauge.
I start the car, and I can see the pressure is about 3 bar (~43psi), but after a little time, the pressure starts to decrease and ends with the pressure is showing 0.
My wideband also shows the effect of this, because the car is idling/reving very lean...

I'm in doubt what cause this problem. The fuel pump is only 14 days old, where the fuel pressure regulator is some years old. The fuel pressure regulator is not leaking at all, not from the seal or the vacuum port...
Earlier today I cleaned the fuel pressure regulator and this was helping a little in the beginning, but the problem went back..

Could it be that the fuel pressure regulator is gone bad, after installing the new 044 pump which are a flowing much more than the stock fuel pump? I'm thinking about the diaphragm is not looking in so good condition, could this cause the pressure to drop, or would i rise with a bad diaphragm?
Or could it be, that the fuel pump doesn't get fuel enough from the tank, because of a problem with the feeding line?

[kjones6039]

If you are confident in the pump, I would certainly be looking carefully at the regulator. Particularly in light of the fact that you seem to be skeptical of it's condition.

Not much help of course, but just a thought.

Ken

[duxthe1]

Any possibility you are pulling a vacuum in the fuel tank?

[djsteffen86]

Yes I also suspect the regulator, i'm just in doubt if a bad diaphragm would cause the fuel pressure to rise or fall ?

According to vacuum in the fuel tank, I don't think this is the issue, since I have tried to remove the fuel cap with no effect.. The fuel pressure stills drop.

[LAV1000]

You did replace the fuel pump, but how about (all) the filters ?
If you have a separated FPR set up you could try to block the hose to the FPR and see if pump stil works.

[jsmcortina]

Unhook the return line.

If there's no fuel flowing to the tank and the pressure is zero, then the pump isn't supplying anything for some reason.

If there's plenty of fuel flowing, block it off (briefly) and see if the pressure rises. That would indicate a regulator that's just allowing everything to bypass.

James