Sucking air/Losing prime

[chris142]

Sunday we were in the mountains and the truck started running bad. Acted like I was running out of fuel. I switched tanks and it cleared up. We stopped for lunch and the truck started and died. I thought maybe it still had air in it somewhere. Drove home fine. Went to leave for work this morning and same thing. Start and die. Took lots of cranking to get it started. Drove to the gas station for fuel. Filled both tanks and It didn't want to start there. Got to work. went to lunch and same thing. Start,die and lots of cranking to get it started again.

The return lines and caps are dry as is everything else I can see. Where do I look?

 

[Cubey]

What altitude? My NA F250 had bad problems above about 9,500-10,000 feet in Colorado. It was very hard to restart if turned off.

Once I got down around 9k it was fine again.

It's just how these trucks are at 9500+ feet. High altitude calls for major IP adjustments. Not worth it if you are there for one day.

 

[franklin2]

Check the top of your fuel filter and see if it's wet with fuel. The fuel heater has a o-ring that likes to leak. There is a line or two running around the injection pump that can leak also.

 

[chris142]

i live @3100ft. We went to about 7000ft. But we make this trip often and this was the first time I had trouble. I dont see anything wet around the filter.

 

[Cubey]

i live @3100ft. We went to about 7000ft. But we make this trip often and this was the first time I had trouble. I dont see anything wet around the filter.

Try replacing the filter? Maybe you coincidentally got some bad fuel.

 

[IDIBRONCO]

What altitude? My NA F250 had bad problems above about 9,500-10,000 feet in Colorado. It was very hard to restart if turned off.

Once I got down around 9k it was fine again.

It's just how these trucks are at 9500+ feet. High altitude calls for major IP adjustments. Not worth it if you are there for one day.

I had the same issue back in June with mine. High altitude is funny. I've seen things leak at high altitude that don't leak down low.

 

[Thewespaul]

https://classicdieseldesigns.com/collections/fuel-delivery/products/billet-3-8-check-valve

This will cure a siphoning situation like what you’re experiencing. Think of your fuel system like a straw with your finger over one end and it full of diesel. If there’s a pinhole leak in the straw, the diesel won’t leak out the hole, but allow air to come in and fill the space that the heavy diesel occupied, exactly like what your truck and many other IDIs experience. Not enough of a leak to physically leak when running, but plenty to draw air in when the truck is shut off.

 

[Randy Bush]

Wes would these be installed before the mechanical fuel pump. Just ordered a couple for my trucks. Great price!

 

[Thewespaul]

Just before the lift pump is good, holds pressure in the whole system that way.

 

[PROFG]

Would after LP prevent leaky diaphragm to crankcase and be just as good for drainback? Will order 2 to start.

 

[Thewespaul]

It wouldn’t, the lift pump is below the level of the tanks so if the diaphragm is ruptured you’re going to get fuel in the crank case no matter what since it’s being gravity fed, and there’s already a soft line in front of the lift pump so it’s an easy place to install the check valve.

 

[PROFG]

Ok, so really need a stop valve before LP even if using parallel epump. This would stop LP from leaking to crankcase when shutoff or running with epump. Could be electric operated same circuit as epump. But, how does a check valve on LP inlet also prevent tank draining to crankcase unless it has more restriction than LP inlet check?? More restriction not a good thing.

edit: changed last sentence since reread sounded snotty

 

[franklin2]

We need to try out a electric solenoid valve on the return line at the back of the engine. That would really stop any pathways back to the tank for the fuel to go. Tie it in with the wire going to the injection pump.

 

[PROFG]

I'm confused (not the first time ). So we are not worried about drainback thru supply but mainly the return? Then why need a check valve after LP? Or do we need both? A solenoid stop at return T and check valve after LP then to seal fuel in system, which might expand and blow off hose . I think I saw somewhere pressure limit for injector return system of 5psi.

edit: Added last sentence

 

[Thewespaul]

There’s already a check in the return at the pump return fitting that keeps the majority of the fuel in the system, and as long as the return lines are tight the return will be fine. The supply side is the problematic one since there is no check valve from the factory, and with the fuel filter being the highest point in the fuel system it’s very easy to loose prime.

If you are running both the electric and mechanical pump, I would run them in parallel with a check valve in front of ether pump and one after the mechanical pump, to keep the e pump from pushing fuel back into the mech pump.