Any ideas on adjusting fuel pressure?

[bigfootchiro]

After weeks of chasing down the gremlins, they have mostly been destroyed and the truck runs great! Still have a cylinder 4 misfire at idle that runs up to a 30+ count once warm, but other cylinders do not misfire at all at any RPM. When this first happened, the guy that worked on my Hoe said he had a "makeshift way of increasing fuel pressure," and when he increased it to 60 PSI, the misfires would stop completely. I'm running at 51 with the MPFI and new AC Delco GFV pump. From what I've read, no one makes an AFPR for the Vortec. I'm going to keep digging deep this weekend and see what I find. Still have the old MPFI unit, so I'll take the regulator off and see what can be done.

In the mean time, does anyone have any experience or ideas as to increasing fuel pressure? Thank you in advance!

 

[bigfootchiro]

BUMP!

Any ideas? I've heard of people running a ported stock FPR and adding an adjustable fuel pressure regulator outside of the plenum, but not sure if that's just marine intakes. I pulled the FPR off the old MPFI, but there was no screw. Tried taking pliers to the tiny port and twisting it, but I don't think twisting it did anything internally, just spun.

 

[iCajun]

Is this one of the little round regulators, about the diameter of a quarter, an inch or so tall and held in with a snap ring? If so, I got one from the DIY junkyard a while back from a Cadillac Northstar engine for a couple of dollars. Remove the plastic cover on top of the engine and it is out in the open, no tools required to remove it. They have the pressure adjusting screw but I don't know the pressure limits, think I have run about 40-55psi with mine while chasing a mixture problem. Thanks, Alan

 

[swathdiver]

Before we had AFPRs some fellas would place them in a vise and put a socket over the top and gently tap it down, compressing the spring inside. Of course we had to use a fuel pressure gauge and put it back on the car to see how much we got with every whack of the hammer.

I just noticed what era your truck is, those old multiport motors should have had adjustable regulators available from the aftermarket. My LC9 runs at 43psi. My old Buick's ran at 32-36 psi but they did not have returnless systems.

 

[bigfootchiro]

Sorry for late reply. I upgraded to MPFI which does not have an adjustable regulator. Does that Cadillac North Star interchange? I've looked all over for an AFPR but no luck. How does that hammering work? I assume from inside toward outside, meaning side that goes inside injection unit toward outside

 

[iCajun]

Copied this photo from Napa 219843 but it looks like mine from the Northstar. I'm not sure about the interchange as I have it in a 502 Ramjet at 55 psi I'm converting to Megasquirt MS3X. Thanks, Alan