Hey all,

This is going to be a big long-winded, but read it all if you want to fully understand my problem...

I have an aftermarket FPR, rails, 63# injectors, twin Walbros, -8AN stainless feed, and am using the stock feed as a return. Everything works, but not as you would expect. The issue is that the FPR doesn't bleed fuel pressure off as fast as it should.

When the fuel system described above was put on the car, it was to feed a Procharged LS1 running 14psi of boost. When the car was at the tuner, they were saying that it was running out of pump because the fuel pressure would quickly fall from the set 58psi to about 53psi at WOT... even at relatively low RPMs. Ultimately, we boost-referenced the regular and got the car tuned. With the regulator boost-referenced, it makes 61psi at 7k RPM. So, clearly, it was not running out of pump when it was falling from 58psi to 53psi originally.

I believe that the problem is the regulator literally doesn't bleed fuel pressure fast enough. I believe that it was actually set to give me 53psi, but it wasn't able to relieve pressure, so pressure built up beyond that to 58psi. Then, when the engine started consuming a significant amount of fuel, it was able to keep it down to 53psi. It was clear from watching the car that fuel pressure fell early in a pull and then stopped at some point and held that pressure for the rest of the pull.

It's all good now one would think. However, I'm beginning to learn how to tune, and I'd really like to be able to tune with a consistent fuel pressure at first and not boost reference it. (I know there's going to be a lot of nay-sayers suggesting to boost reference, but let's stay on topic here... the FPR problem). Even if I do keep it boost referenced, it's not giving me a consisent 1:1 ratio. I am making about 45psi of fuel pressure with 12psi of vacuum in the manifold and only 61psi at 14psi of boost. That means (based on my deductions) that the regulator should be giving me more like 35psi of fuel pressure at an idle (12psi of vacuum) instead of 45psi.

What do you guys suggest? Is there another regulator that someone would recommend that might not exhibit this issue? Perhaps the solution is a Hobbs switch on the second pump? Perhaps I should up the pressure to something over 60psi and hope that the regulator is able to relieve pressure fast enough to give me a consistent fuel pressure?

 

What's the make and model of FPR?

 

First, lets try to get all the details...

Vacuum is rated in inches, not PSI. 1in. vacuum is roughly .5psi...
With that said, if you idle at 12in vacuum, the reference should lower your fuel pressure about 6psi.

Remove vac line & set to 58 with car running. Connect the vac line & it should be at about 52 assuming you have 12in at idle.

Now get into boost.... 58psi fuel pressure +14#boost should be 72psi.

The key is to properly set your base pressure then post some numbers at various boost levels.

Assembled properly, the pumps will outflow your injectors.

Considering you were losing pressure with the regulator not boost referenced, dropping from 58 to 53, something is not right. It should have held 58 across the board. If you are running both pumps continuously, that could be messing up your idle fuel pressure, by overloading the regulator or return line.

 

I'm pretty sure the regulator is an Edelbrock PN 1728.


That's good info. I always wondered how I was getting more than 14psi of vacuum when decelerating... seemed impossible... obviously, it was.


I think this is the problem. Should I set up a new feed, new regulator, both, or just do the Hobbs switch on the second pump?

 

Turn off 1 pump & see what difference it makes.
Personally I never recommend to run 2 pumps continuously.

If you are interested in lines or upgrades, give me a call. I have everything you need to upgrade your system.