I have a 2001 Silverado with a 5.3 that is currently N/A but soon to be turbo'd and I'm trying to figure out my fuel pressure problems before I go into the world of boost. So first, some info:

Set up is a single Walbro 400lph in an NBS fuel bucket that goes through a new stock fuel filter, stock lines, stock rails, Aeromotive 13129 FPR in line of return using "-6 to quick disconnect" fittings and then using the stock return line to go back to the pump. I also installed a racetronix hotwire kit so the pump has plenty of power for its amp draw and stock regulator block off plate.

The issue at hand is that with the truck running and vacuum reference port unplugged, I have the base pressure set to 58psi. When I reconnect the vacuum line to the regulator, I drop to 55psi. Truck is cammed and typically runs about 8-9psi (58-60kpa) of vacuum at idle (228/232 Sloppy Cam). I know the regulator rises with boost at a 1:1 ratio but not sure if I should be seeing the same reduction rate with vacuum which would put me at 53-52 psi at idle which seems more correct. I have a fuel pressure gauge in the fuel rail schrader valve that works and is accurate inside the truck so I can easily monitor changes while I drive. What I'm seeing is that fuel pressure does not rise to the base pressure when at WOT and will actually drop to about 49psi. Also when driving around, the pressure doesn't seem to fluctuate with changes in load as it's supposed to.

So I had some time tonight to do a few tests using hptuners to run the pump continuously and my fuel gauge to view pressure:
-First was the entire system hooked up as listed above with the regulator adjustment screw all the way out (lowest pressure possible) equaling a pressure of 42psi
-Second test was with all the lines hooked up like normal with no regulator (stock one blocked off and aeromotive bypassed) and equaled a pressure of 41psi (very minimal)
-Last test was the same as the second but I removed the tank pressure sensor and return line connection at the fuel hat and directed it into the tank via the pressure sensors hole, thereby eliminating the stock fuel return route through the fuel hat and "leg" of the pump bucket. This equaled 31psi.

I'm personally under the impression that I'm dealing with a "False High Pressure" situation as described on Aeromotive's website but there's so many folks running this set up that don't seem to have these issues. Especially with having an AFPR. So does anything jump out to anyone as a red flag on my set up or have any insights on trouble areas with these trucks and setting this system up? Thanks and I welcome any comments or questions.

 

Did you use submersible rubber fuel hose in the tank? It is notorious for being a pile of poop and splitting or developing other leaks. OEM corrugated nylon tube seems to be the most reliable.

It's unlikely that your regulator is bad, you would see gasoline in the vacuum hose if the diaphragm was bad. Just to check your set up, what is your vacuum source?

If you could restrict the return from the regulator to the tank somehow, you should easily be able to get 100 psi. This would test my theory of a leak in the tank.

 

I used the Gates Submersible fuel line p#27097 ($18 for about 12 inches) and stainless fuel injection hose clamps for the intank connection. I wish we could reuse that stock stuff with out tearing it up to get it off.

And no fuel in vacuum port so the diaphragm is good. Vacuum source is coming off of the original port that was used for the stock regulator. I’m using a pretty stiff hose for that line to eliminate any chance of vacuum collapsing it.

When I return home from work today, I’ll try blocking off the fuel pump to check for in tank leaks as you said. Shouldn’t be hard to do. When the truck primes it holds about 20 pounds in the rails and very slowly falls off

 

Okay Mike. I clamped the fuel return line just after the pressure regulator and pressure maxed out my gauge at 100. I let it sit for about 30 seconds and pressure did not come down so the feed seems to be holding up well. Unless it was above the 100 mark and it didn't come down fast enough for me to see it.

 

Try retesting with the shrader valve core removed.

 

The tests I ran were with the core removed. I have an adapter that uses the port for the pressure sending unit and it requires removing the the valve core.

 

After testing pressure using a Mityvac for vacuum and verifying the regulator's operation, maybe even test with a few psi pressure to the vacuum line to see fuel pressure rise.If the regulator regulates, try a different vacuum source.
After that, I will step aside and let someone else make suggestions.

 

I have a MityVac so I’ll try that this evening and see what happens. Although I never suspected the regulator to be an issue, they do go through a lot between the assembly line and your doorstep.

I’m running a factory intake. Where else would a person hook up the vac source? Or would drilling and installing a barb be more ideal?

I’ll report back the results tonight. Thank you for the troubleshooting Mike. It’s much appreciated.

 

It's been so long since I've had my original truck manifold, where is the vacuum port for the stock regulator?

 

Stock location is on the drivers side right in the middle and above where the stock regulator resides.
The port is fairly large (Maybe 3/8ths) and I’m using the stock rubber elbow that also reduces the size to about 1/4 inch and I run that to the regulator which is a snug fit over the barb fitting.