Renix Fuel Pressure Letdown Checkvalve

[knever3]

My renix stroker is not keeping fuel pressure to the rail.  It's a '87 Renix system with a '95 fuel rail with return and a Hesco adjustable FPR.  When I shut the engine off the fuel pressure drops to Zero. 

 

I have these questions:

 

Do I need to buy a new fuel pump? 

Is the check valve in the pump?

How does the new Hesco adjustable FPR allow more fuel to the engine without the pressure increasing like the old vacuum one did?

 

The last one really has me stumped.

 

 

 

[HOrnbrod]

My renix stroker is not keeping fuel pressure to the rail.  It's a '87 Renix system with a '95 fuel rail with return and a Hesco adjustable FPR.  When I shut the engine off the fuel pressure drops to Zero. 

 

I have these questions:

 

Do I need to buy a new fuel pump? 

Is the check valve in the pump?

How does the new Hesco adjustable FPR allow more fuel to the engine without the pressure increasing like the old vacuum one did?

 

The last one really has me stumped.

 

Don't understand what you are asking. For the HOs, hook up a pressure gauge on the rail, pull the vacuum hose off the regulator, screw the adjuster screw in, and the fuel pressure increases exponentially w. vac / wo. vac to the regulator. The increased pressure forces more fuel through the injectors as indicated on the A/F gauge. ASSume the Renix version works the same way if that's the one you are using.

 

As far as the check valve, you can install an external in-line fuel check valve if the one in the pump is shot. I haven't done it, but others have.   http://www.cherokeeforum.com/f2/fuel-pump-check-valve-21921/

[knever3]

I have the Renix system, so the Hesco adjustable fuel pressure regulator doesn't use vacuum anymore so you just set the fuel pressure and leave it.  That doesn't really make sense to me since the engine would need more fuel when revs/load increases.  It just can't seem to be adjusted purely by injector pulse width.  I hope I don't have the lines on backwards, supply to return or I'm missing something?

 

As for the check valve that's a great idea, I'll check out that link thanks.

[Keyav8r]

You're confusing flow with pressure. The fuel flow from the pump is fairly constant at any engine speed as it is driven by a fixed speed electric motor. Pressure is created when the flow is blocked or partially blocked. That is the purpose of the fuel pressure regulator. It maintains a fairly constant pressure on the fuel rail by controlling how much fuel goes back to the tank through the return line.

 

 

At idle the regulator is more open and there is a higher fuel flow back to the tank, lower fuel flow to the injectors.

 

As RPM increases and more fuel is demanded by the injectors, the valve closes and allows less fuel flow back to the tank.

 

The regulator balances the fuel flow between the injectors and the return line to maintain fuel rail pressure.