Resolved Another fuel pressure drop thread

[DroopYeyeS]

I've been having an issue with the car, since I got it back on the road 2 weeks ago, with fuel pressure. I've read the other threads of this nature, but most seem to be about pressure bleeding off after shut down. My issue is while running.
I am suffering from a serious drop in fuel pressure any time I get near and/or above 30% throttle. I watched the gauge on my Areomotive AFPR last night while testing, and my pressure begins to build as I ease into the throttle. I can get up to about 50psi on the gauge, which is right at that 30% mark, then it plumets to 18psi in less than a second.
I thought perhaps I was suffering from the voltage drop on the fuel pump, so I did my rewire last night. This had no effect on the issue at hand. Also on the fuel pump side, I have replumbed the sender with my walbro 190 and -6AN fittings. I have a section of fuel line going straight from the output tube on the pump, to the fitting going out of the sender.
The AFPR & fuel filter are only about 6 months old, so I would assume they are still ok. I guess I could pull teh AFPR apart and check it out.
Any other ideas as to what could be causing this drop under load? Also I forgot to clarify that this happens with or without the vaccuum line hooked to the AFPR.

 

[Calan]

Is it rising 1-to-1 until it collapses?

It sounds like it holds pressure until it hits a crack point, and then bleeds off. That would point me towards the pump outlet (broken o-ring?), pump itself, or maybe something in the AFPR.... if the voltage is remaining stable and there is no sign of a leak.

Do you have the ability to turn on the pump with the car off, and inject a known amount of air pressure into the AFPR? If so, you can do some testing and get a better understanding of exactly when it happens.

 

[bryanwheat]

IT's got to be in the regulator, pump, or the hose from pump to bulkhead.

 

[DSM Jeff]

Do you have a rubber hose connected to the pump, then to a fitting on the sending unit?

 

[DroopYeyeS]

Calan: Yes it's rising 1:1 until it just drops. There is no O-ring, as I have a section of hose straight from the pump to the upper plate of the sender. Good idea on turning the pump on while the car is off. I can do this, and hadn't thought of that for testing. I will get on that this weekend. Thanks for that idea.

Jeff: Yes, it's hose straight off the pump to a -6AN fitting plumbed into the upper plate on the sender.

 

[Calan]

The more I think about this, the more it sounds like the high pressure relief valve in the pump has failed, allowing pressure to bleed off too soon. (Assuming it's the same design as the 255 pumps).

I've had it happen on both a Walbro 255hp and a brand new Deatschwerks pump, although it was higher than 50 psi.

 

[DroopYeyeS]

Ok, so I did some more tests this weekend on the fuel system. I had a friend turn the pump on while I inspected the system for leaks. Nothing visible showed it's self. I did try clamping the fuel return line shut. This raised FP at idle to around 60psi, but again at 30% throttle it dropped like a rock. I am now looking at either a clogged filter, or as Calan suggested.
On another note, I did notice that my intake is under vaccuum at 6psi of boost and up. This is causing my BOV to open fully right away. When I take the vacuum line off the BOV, it holds shut. Also when my thumb is plugging the vacuum line, I can feel it pulling vacuum opposed to building pressure.
Any ideas on this one?

Update:
I went out to start looking for possible vacuum leaks, and/or anything else that may cause this issue, last night. When I started the car, it idled rough for a moment, then smoothed out. I began to rev it manually at the TB to see where the drop was happening. Out of nowhere, the pressure is not dropping the way it was. I revved it up to red line at WOT, with no dip. Not sure if there was simply a clog or what the deal is, but this is where it now stands. Will update when/if it occurs again.

2nd update:
So I went out at lunch to try it again. Issue is back. Back to square 1.

 

[DroopYeyeS]

Issue solved. The strainer on the pump it's self managed to get clogged. New strainer, and she's back to normal. Thanks for the input everyone.