low fuel pressure

[netman555]

hi hope some one can help,afriend has a merc 454 magnum 7.4ltr bigblock,year 98 or99,fuel injected motor, fitted fuel pressure gauge to fuel rail ,fitted a new pressure regulater to rail,at idle reads 20psi,bring the rpm to 2000 and it sits at 15psi,remove the vac hose from regulater at idle and pressure goes to around 30psi,if he blocks the return line it reads full pump pressure 80psi,any help would be great,thanks john.<br /> john_ellis@clear.net.nz

 

[gss036]

Re: low fuel pressure

WRONG string, belongs on inboard string. JB please move.

 

[Yepblaze]

Re: low fuel pressure

So what is your concern? <br /><br />Those numbers and results might sound about right.<br /><br />Does your manual call for higher running pressures? If so, it sounds like a new pressure regulator might help. But again, what is the spec calling for at idle and no load 2000 RPM.<br /><br />You see if you go wide open throttle the vacuum drops (like pulling the hose) and increases the pressure.<br /><br />And it sounds like your fuel pump is capable of 80 psi.<br /><br />I'm not seeing the issue.