Ok, so I have a 2000 NBS and it is the return style system that I ran a new feed line from the tank to the OEM rails. I also pulled the stock return line off and put an aeromotive FPR in line. Lastly, I bypassed the OEM regulator with a custom piece with some diagrams on here from boostedsl2.

The weird part to this is that when I turn on ACC, the pressure will build to around 75-80psi and then just drop to below 20. If I start the truck, the pressure will stay constant. Is this normal for aftermarket FPRs?

Also, is it normal that I have to adjust the screw on the regulator and then re-prime the pump to see the difference, i.e. I can't just turn it while the ACC is on and see the difference.

Overall, the truck will idle, just have a concern as to why it won't prime without engine running...

 

Its not an FPR issue, its with the pump. Its normal to drop pressure quickly, however it should only go up to what the regulator is set. The difference in pressure between the engine on and off should be very small. You can get the pressure close with the engine off, but to really set it you need to have the engine ideling and the vacum line disconnected. Once its set, reconnect the vacum line. When you pull the line it will probably idle like crap, but the adjustment should only take a second.

 

Well, the thing is, the pressure was good with the engine off before I put the aftermarket FPR in. I am seeing VERY low pressures with the engine off, but with it on, I have good pressure. Is that part normal?

 

I have a MagnaFuel regulator, and they explained that what you are describing is normal. The regulator will allow pressure to bleed through because it has no check valve. Apparently the stock regulator does. MagnaFuel said that if I want to retain some pressure so that the truck starts like stock, to install check valves between the fuel rail and regulator. The check has to have a low cracking pressure, like 1/2 psi, so that it doesn't influence pressure.
When you turn the key on, the pump only primes, which is running for like three seconds. If you listen, you will hear the pump run for a few seconds. You can check the pressure if you keep turning the key off and back on again quickly. each time the pump cycles.

 

Yeah, that makes sense. I appreciate it Mike. The only way I have found to adjust the pressure was to actually start the truck. I finally got it pretty close to 58psi at idle just by starting it and checking the pressure, then adjusting without the vac line. The next thing is to get the vac line hooked up and then mount the regulator. I think I am going to have to make a custom bracket as just using the one that came with the regulator onto the firewall is not going to work like I wanted.

On another note, I think the aluminum elbows fixed my stalling issues!!