A little history: A few years ago I put a vacuum guage on the fuel line before the fuel pump and found I had an obstruction on the fuel pick up. Hutch mod took care of that . I then put a pressure guage on the fuel filter bowl and found I had a pressure reading of only a little over 40 PSI. I tried cleaning the FPR and the screen on the side of the fuel bowl and changing the fuel filter, but long story short, the pressure never went much higher. I moved the guage to where I could see it while driving. The pressure fluctuates between 40-50 both at idle and while driving conservatively. If I really get on the throttle or when going up an incline, especially pulling a load, it's not uncommon to see the pressure guage drop to around 30 PSI and to feel the truck hesitate just ever so slightly.

I consulted two diesel mechanics who specialize in PSDs and they both felt the fuel pump may be going, but they both suggested I wait until a "real" problem surfaces. They said 50-55 PSI is spec, but once again, wait until there is a real drivability issue. Neither of them seemed to indicate that the low fuel pressure would cause any problem.

That leads me to a recent post I saw (I can't find it for the life of me now) where a member said the Ford dealer told him his injectors were shot due to low fuel pressure causing the injectors to burn themeselves up. Reading that got me motivated to try and remedy the fuel pressure issue, which led me to doing the FPR shim. I had plenty of BBs lying around, I didn't need to do any machining to them, so I used a BB to do the shim, but no change. The pressure stayed the same at 40-50, and dropping when I get on the throttle. Figuring it could be the fuel pump just dying a slow death, I replaced it with a new OEM pump. Still, no change! The pressure rose maybe 2 PSI, but not enough to call the problem "fixed."

What else would control the pressure reading I am seeing at the fuel filter bowl?

 

The FPR controls the fuel pressure. That's why it's called the Fuel Pressure Regulator.

Let's start by telling us where you have the fuel pressure gauge hooked up? A port in the fuel bowl? Have you tried any larger shims than a bb?

 

If you are pulling fuel pressure that low shimming will only mask the problem, if it even does more than just increases your psi at idle. Low fuel pressure can definatley hurt your injectors if allowed to continue. You need to take a look and make sure all your clamps are tight and that you aren't pinching the fuel line from the tank to the hard line. Have you tried using a line around your pre-pump filter? Have you checked to make sure your FPR o-ring isn't split or chewed up?

 

I know this maybe the wrong way to go fixing your problem.. but David at Diesel Innovations is having a turkeyday sale on RR systems for $349.

Mods feel free to change this if I can't post prices...

Thanks and I hope you figure out ur prob

 

Reading Clay's post, you might need to consider doing the in tank mods if you haven't done them already. Plugged screens in the mixing chamber could also account for this.

 

Don't forget about the possibility of debris coming from the tank also clogging the screen on the inlet of the pump itself.

 

Good replys. Thanks. Let me address them one by one.

F 350-6: Yes, the guage is hooked to a port on the back side of the fuel bowl. I haven't tried any shims larger than a BB as I have read that usually pushes pressure over 100 PSI, which more than I would want anyway. Regarding your second post, tank mods (Hutch & Harpoon) have been done with a larger fuel line run to the OEM fuel pump.

Clay: I realize shimming the FPR will mask a failing fuel pump. That's one reason why I have never bothered to shim the FPR. FPR O-ring looks fine and I don't see any leaks anywhere, so I don't believe I'm losing pressure due to a seal integrity failure in the system. I have a vacuum guage tee'd in just before the fuel pump. That vac guage tells me everything is good right up to the fuel pump; no restrictions as vacuum is low, which rules out the pre-pump filter causing a problem.

Guzzle: I put on a brand new OEM fuel pump without seeing a significant change. In trying to shake something out of the pump I removed, nothing came out. The Dahl 100 filter is just before the pump. I doubt debris would be making it by the Dahl.

 

What kit did you use for the Hutch? Something could've screwed up in the tank again. With a new pump and known good lines, there's nothing but a restriction could be causing that. Check that filter again like Clay said. If you left enough slack, maybe you can just get a double barb and bypass it that way...

 

Are you sure that the FPR plunger and seat are not leaking? If the seat is damaged and leaking back into the return, it won't matter how strong the spring pressure is - your max pressure will be determined by the metered leak past the seat.

 

x2, this is where I would start. Cheap and easy to do.

 

Great point! I guess I need to order a new plunger and seat? Once I get these will it be obvious to me how to install them?

 

Yep, just remove the FPR cap and replace the plunger.

 

here is the kit U need from ford.

FORD part # F81Z-9B249-BB.

it has new plunger, spring, sleeve, and housing oring 65-75 bucks depending on dealer

 

$51.86 at Partsguyed.com if you can wait till Friday or so to get it.

 

I think it's cheaper to try bypassing the filter, just to make sure. At least try it while you wait for the part to get there... LOL