Fuel Problem?

[Barny]

My truck has been dying every once in a while for the last few weeks.
Before I could open the bleeder on the fuel filter, some air would come out and the truck would start right up and be fine for a day or so.
Last week it stopped and I couldn't get it to start again. I got home and it started after a few tries.
Walt said to change the oil pressure switch and the lift pump.
I changed the switch and it would do the same thing but now there are slight power fluctuations especially right before it dies.
Today it died and would not start again so I had it towed again.
I just started it and I have 9lbs of fuel pressure with the engine off and at idle. At 3000rpm the pressure goes down to 4-5lbs. revving up to 3000 it runs ruff but I think that's normal when it i not in gear.
I have a new fuel pump coming from Walt but I don't think thats the problem.
It's a 96 with 360,000 miles and has run perfect up to now. I've had the truck 5 years and this is the first problem other than overheating and Walt's upgrade kit and fan fixed that years ago.

[Barny]

I put the new fuel pump in and it is at 10psi with the key on and with the motor at idle after a few seconds it goes down to 5psi and stays there.
I guess I'll change the filter again and try to make it to work tomorrow.
Maybe it's the new fuel cleaning out the tank and clogging the filters. The slight power fluctuations do feel like a clogged fuel filter. I don't know what else to do.

[Husker 6.5]

I put the new fuel pump in and it is at 10psi with the key on and with the motor at idle after a few seconds it goes down to 5psi and stays there.
I guess I'll change the filter again and try to make it to work tomorrow.
Maybe it's the new fuel cleaning out the tank and clogging the filters. The slight power fluctuations do feel like a clogged fuel filter. I don't know what else to do.

Sounds like it could be the filter on the end of the fuel pickup line in the tank is plugged up. It would flow enough to keep the engine supplied at idle, but would starve the lift pump and IP at higher rpm's/loads. For that check you will have to drop the tank and pull the sender assy from the top of the tank. If you do that, you might as well flush the tank out, too.

Another definite possibility (especially with the milage on the truck) is that you have a pinhole in the fuel line pre-lift pump. It would suck air into the fuel with very minimal leakage of fuel from the line. A thorough visual inspection of the fuel line from the tank to the lift pump wouldn't hurt.

Husker 6.5

[Barny]

Thank's for the reply.
When I changed the pump it was siphoning out of the tank pretty good.
I'm thinking that if the filter is clogged it might give a high pressure reading.
It looks like the IP regulates the pressure down to 5psi when it's running.
When I changed the pump it could of back washed the filter enough to temporarily flow right. The filter in it is only 2 weeks old.
I hope it runs.
Reading all this crap about PMD's is making me paranoid.

[Barny]

Well the fuel filter looked clean to me.
We'll see what hapens tomorrow.

[grancito]

When you say power fluctuations, do you mean power surges? If the power increases before the engine stops, it indicates air getting into the line.

[Barny]

I don't think I've ever noticed a power surge like that.
It acts like it the fuel filter needs to be changed.
I only know for a fact that it had air in the filter the first time it happened. A friend stopped to help and he saw it. After that I assumed that is what was happening because I would open the air bleed and it would start right up. Then I shut it down right away closed the bleeder and it was fine for a few days.
The power fluctuations didn't start untill after I changed the OPS.

[Barny]

Everything seems to be fine sence I changed the fuel pump.