So I have a FRx sitting in my garage that I'm getting ready to install. It comes with 3 springs:


55-60 psi silver spring
61-65 psi gold spring
66-72 psi black spring


From what I've read about fuel pressure anything above 50psi is good. As long as it doesn't drop below 40psi at WOT there is enough fuel to feed the injectors. If that is the case why would I install anything besides the black spring and call it good knowing I'll never get anywhere near 50psi to have any issues? When would you use the silver or gold spring?

 

I plan to do the FRx mod this winter when the truck is in the garage getting a bunch of other efficiency based modifications. Based on my research I have read that the gold one is the preferred spring to use, but could not really tell you why.

I have subscribed in an effort to learn something soon from reading the responses.

 

Here's the rub with these fuel pressure regulator springs:

If you're hammering on the truck and your fuel pressure is dropping at all, the only time the fuel pressure regulator spring will make a difference is at idle and light load.

To put it another way:

If your fuel pressure drops to anything less than the regulated spring rate, you could install a ball valve in the return line and close it off completely during hard acceleration because your regulator is closed anyway.

Again, the only time you'll see increased fuel pressure is when you are at an idle or light load because once the pressure drops below the spring rate, it doesn't matter what spring you have as your pressure will STILL drop.

 

Understood. My question is if there's much of a difference between having that idle/low load fuel pressure set at 58psi (silver spring) or 68psi (black spring). If all I need to do is stay above 50psi does it hurt the system to just toss in the black spring and call it good?

 

You pose an excellent question.

For a stock unit (Stock Injectors), you want to be between 50 psig and 70 psig at idle. So long as the pressure does not fall below 42 psig WOT Loaded you're spot-on the spec. The maximum fuel used is at 35 psig at the testing port on the Head. Anything more does nothing but stress the system. There is no gain.

Why 50 - 70 psig at idle? This is where you want to be.

These are "Return Fuel Systems", with a positive displacement pump impeller (they move the same volume of fuel regardless @ 12 vdc).

The fuel returns to the tank once pressure is obtained via the fuel regulator valve. This is necessary primarily for the life of the Fuel Pump.

The fuel pump derives its cooling from the Fuel moving through it and the ambient temperature surrounding it.

Inadequate cooling greatly shortens the life of the pump. Which is why the PCM shuts off the pump 10-15 seconds if the engine is not started waiting for GP Cycles; continued running would just "burn out".

At idle, higher pressure means less flow and therefore a stressed pump.

The Stock system returns twice as much as it uses to fuel the engine at idle.

I hope this answers your question.

Tom

 

Thomas White....you a great addition here!

 

Tom, excellent description. Thank you.

Do you think it would be beneficial to use the higher psi springs in a colder climate? To send more warm fuel back to the tank......

 

Sure does. Thanks for the education. Reps sent!