Vortec 5.7 Fuel Pressure Normal?

[shovenose]

I've read all over the place it should be 60+ psi all the time and it shouldn't bleed off when you turn off the engine or after you prime it by putting key in on position. Well, I do not have 60 psi and it does bleed off...

Vehicle runs and drives but it doesn't run quite like it should and I'm stuck at 20-25+ long term fuel trims even after a new MAF sensor which several people told me was the problem.

 

[Sparky]

MAF sensor won't fix the fuel pressure. Probably just need a new FPR. They are a vacuum-driven regulator with a diaphragm and that can sometimes wear and/or split, which results in bleed-off, poor pressure, and sometimes even increased fuel usage as it literally sucks extra fuel into the vacuum lines and burns it off.

Easy way to tell if the regulator is bad is to pull the vacuum line from it (engine off), if it smells like fuel (or has any fuel in it at all) then the regulator needs replaced. AC Delco 2172251 or or Delphi FP10075 I think are what you want for the 5.7L vortec.

Oh yeah, and inspect the vacuum line connected to it. Sometimes they split and crack due in part to fuel getting in them possibly, but also just age. and if they are leaking vacuum it can negatively impact fuel pressure even if the regulator itself is ok.

 

[Mooseman]

I find it strange that when you rev it, the pressure goes up slightly. It should go slightly the other way. And it should not bleed off. My vote is also for the FPR and/or the vacuum line to it.

 

[shovenose]

isn't that fuel pressure regulator under the upper intake and part of the fuel injection spider that i replaced? pretty sure it doesn't have a vacuum line on it, as it's exposed to manifold vacuum... old one didn't, unless i'm thinking of something else. if that thing is defective i'm going to get really, really angry.

what i didn't really show well in the video is if you hold it revved up yes the pressure goes up a little at first but then it goes back down even as rpms stay the same

 

[Mooseman]

I did see that and still find that abnormal.

I know what you're talking about. Had the same spider system in my old 93 Blazer 4.2 that I also replaced. It was so common that the dealer had it in stock. I can't remember if it had an external FPR or not. You have a manual that explains the system?

 

[littleblazer]

The FPR on the 5.7 vortec is on the spider in the upper intake. Vacuum is driven from manifold vacuum inside. It is biased by it iirc.

 

[shovenose]

The FPR on the 5.7 vortec is on the spider in the upper intake. Vacuum is driven from manifold vacuum inside. It is biased by it iirc.

Thing is it's new :'( I think I'll pop off the intake tube and see if I smell raw gas through the throttle body to tell if fuel is leaking in there.

 

[mrrsm]

IIRC... When you R&Rd it... That Spider EFI was New from your business... but not an OEM version... Yes? Has the Fuel Filter also been replaced?

 

[shovenose]

IIRC... When you R&Rd it... That Spider EFI was New from your business... but not an OEM version... Yes? Has the Fuel Filter also been replaced?

BWD from O'Somewhere on that fuel spider. And today yes I did replace the fuel filter. No change in fuel pressure.

 

[eightshot627]

On my 96s normal fuel pressure was 57-58psi. At 55psi it was hard to start. If it does make 57psi replace the pump.

Good Luck,
Walt

 

[mrrsm]

Only because we seldom run into issues relating to the "Spider" Style Fuel Injection System for NA 5.7L Engines... THIS Video from James Danner is Chock Full of more Diagnostic Stuff AND focuses on GM's Upgraded EFI "Spider"...Loaded with Diagnostic Goodies and some Close-Ups & Stuff for our Early Model Work Truck Owner-Members.

James took the time at the end of this Video to "Autopsy" the Original "Spider" EFI Device and provide an uncommonly detailed view of this Mysterious EFI System in a Bench Test Demo. Note that the Upgrade moved the otherwise side-by-side arrangement of the OEM "Spider" EFIs in its delivery manifold out and to the extreme ends of the Fuel Feed Tubes . This was probably done to allow the Fuel Injection Force to propel Atomized Fuel more readily into the Opened Intake Valve Ports of the Dual Engine Heads:

And... You can get a Bird's Eye View of the what Nominal Fuel Pressure looks like during the Fuel Injector Balance Test! :>)

Dr. Shock shows us How to Rebuild The GM OEM "Spider" CSFI EFIs: