I posted this a month ago...

I have run about 2500 miles and still have the problem. I ran the vacuum gauge for 1000miles and it looks fine. I pulled the tank again and made sure everything in the pickup was working. I replaced the lift pump again. I totally bypassed everything before the lift pump with a single piece of 3/8" fuel hose and a weighted end thru the filler port. It seems like the easier I made it for the pump to suck fuel and the more I babied it while under load the better it did.

I am thinking it might be sucking air and cavitating the pump? The gauge gets bouncy as the fuel pressure goes down, it has a 3 psi pressure surge when you turn it off when low on pressure, and after letting it sit for a bit the gauge has a second or so of no pressure before it comes up after you start the truck. But I have replaced everything on the suction side and no one seems to think it can suck air while running on the pressure side. I do have some very small fuel leaks on the pressure side but I have no power issues and no starting issues.

I did pinch off the return hose while the fuel pressure was about .5 psi and it went right up to 4psi. Now on a second gen this would tell me the fuel restrictor valve on the fuel return port of the injection pump is bad. Is there something like that on the first gen trucks? I can find any info on it

Thanks for the help guys
ROB

 

That does not make any sense, the VE has a fixed orifice that serves to maintain case pressure in the pump but it should not affect fuel pressure. I think the lift pump is weak.

 

Wannadiesel, what about the cam? but wouldn,t that be consistant?

 

Rob - I'm having the SAME issues with a piston LP, but it never goes to zero pressure, it just bounces really bad, and that bounce is indicative of less power. I replaced the entire pick up assembly, new supply line, on my 3rd piston LP, the fuel heater seal, all banjo seals and it still does it.

The fixed orifice Wannadiesel talks about is the return line banjo with the screen. That's really the only thing I have not replaced.

 

I here you Jeff! Whatever is going wrong with the rig it's not obvious and that really sucks. I would love to just be able to replace something and have it fixed. I had the bad bounce before I put in a needle valve; but now it goes from rock steady to somewhere less than a 1psi bounce. I don't feel much of a lack of power but I also baby it when I am low on fuel pressure. I don't want to burn up an injection pump!

So you say fixed orifice with a screen. Could it be possible that the screen is gone and that as the fuel warms up (the tank fluid would warm as you drive because of the warm return fuel) it's easier for the fuel to flow and causes a pressure drop because of the lack of restriction? I know it's a stretch but I'm on my 4th fuel pump now.

I have had the problem when letting the truck basically sit and idle for 1/2 hour while unloading things at night. I do think it's getting worse and to the point that I can't just live with it anymore. Last weekend it ran 1psi or less for half of a 90 mile trip with only 700lbs in the bed (it had no problem the day before going the other direction). I really had to baby (down to 50mph on a 75mph road) it to keep it above zero on any kind of hill.

Yep Bencie the cam would be consistent and if it went down the pressure should never come back.

I have been thinking about just getting a piston pump but if it did work I think it would be just masking the problem.

 

I'm like Wanna I'm not sure how it could affect it - I was thinking all along the problem was my VE dying and it somehow pushing fuel back the other way, which I know sounds crazy, but I had replaced EVERYTHING, and had the VE rebuilt two weeks ago, and its doing the same thing. The shop told me that return banjo keeps the pressure in the VE regulated, and that regulated pressure also affects the timing advance as well as more things I'm too ingorant to know. Either way, mine was a little dirty - I had eat a shutdown solenoid so there was some of that particulate in the screen, but the orifice was not stopped up.

Another odd thing that I noticed over the weekend, is I plumbed in a clear inline fuel filter and placed it on the suction side of the LP, just to catch any big particulate from the tank, and it won't even fill it up, plus if I run it very long it'll drain it completely and only leave just a wee little bit of fuel in it.

I can unhook any line and allow air into the system, like pull the supply line from the LP - let it sit for a while, crank the truck and it pegs my gauge at 15 PSI, only pulls the truck down smoothly to around 14 PSI and pulls HARD, but a few miles down the road, sometimes 2, others 20, it starts erratically bouncing any time I get into the pedal, and if I drive it 30 miles to work, by the time I set my cruise for 10 minutes or so you can hear the engine starving for fuel.

 

im having the same problem with my 4bt.My pressure gets better as the fuel level in the tank goes down.Under an 1/8 tank i have full pressure.