When I let the fuel tank get low enough and park at the wrong angel on uneven ground, the end of the return line becomes exposed. This can allow air in, and fuel out. When this happens it can drain the Fuel from the injection pump housing.
Thankfully, this has only happened a couple times, as the manual primer lever is not in the most convenient location.

At least it's my theory that the return line is the cause, as I never have any loss of prime above 1/4 tank no matter how long it sits. Under that level, I have had to prime it after as little as an hour, and had an episode of extended cranking after just 10 minutes.
Every incident has had 2 things in common, less than quarter tank and parked on an uphill angle.
Parked at the same angle with higher fuel level never causes an issue.

 

It is good to see you know when this happens but the return draining to cause a hard start I cant really see.
So what if the return was empty from injectors to tank it should not cause any issues as it is not on the PSI side.
Now if from the tank to the injection pump was to drain back when under 1/4 tank I can see that to be a cause.

What if you were to pinch off the return line some place as a test to see if that helps? Or have you done that and why you know the return is the cause?
Now if you find it is the other side maybe install a spring loaded check valve as close to the tank you can.
Just the way I see it is all
Dave ----

 

The return line comes from the top of the injection pump, tee's into the return from the injectors, then goes to the front part of the tank.
I have not done anything in the way of testing it, aside from avoiding running the tank below the quarter mark. Even with daily driving, it can take 2-3weeks to get that low.
I have always tended to avoid running a fuel tank below the quarter mark before refilling, so this issue took a while to show up or recur.
the overflow valve at the injection pump return connection has a spring loaded check ball, but is designed to open at around 10psi. It's quite likely that it can allow air in after the return line has drained out.
I did have to change the lift pump due to a leaking condition. That could have been a contributing factor, as I have not had any further issues since, but I also have not run the fuel low either.

The last incident occurred after having driven about 100 miles and then stopping to refill. I had to wait about 10 minutes in line before they turned on the pump. After I refueled, it took 10-15 seconds of cranking to start. I've not run the tank that low since. Of course, that was also prior to the lift pump replacement.

 

It should really not be a problem. It sounds like it works like the Ford idi system. You can take a straw, put it down in a drink, put your thumb over the top of the straw, pull the straw up and out of the drink, and the drink will stay in the straw forever, as long as you hold your thumb over the top to seal it off.

That is how the idi system works, and it sounds like the older cummins is the same way. The fuel actually "hangs" there in the return line and the top of the engine. Any little air leak in the fittings and such up around the engine is what lets air in, which lets the fuel slowly dribble back to the tank through the return line.

I keep telling people on another diesel board I am a member of, that someone should try a solenoid in the return line up near the top of the engine hook to the ignition switch. Turn the switch off, the solenoid blocks the return line so even if you did get a air leak the fuel would have no where to go, so the system would stay full. Turn the ignition on and the solenoid opens letting the system work as normal. I haven't tried it yet, and no one else has either. I just had a though the other dayfor a solenoid, we could use the simple 3 port tank switching valve made for these trucks with dual tanks and a carb with no return lines. We could plug off the port that is open with no power to the solenoid, and use the other two ports that would be open when the solenoid had 12v.

 

I never updated about the cause of the air intrusion. Turned out to be the faulty lift pump. I have no clue why it only occurred when the tank was low on fuel, but after replacing the lift pump, it no longer happens.

 

Where have you been, Paul? Will I see you at the Truck Show in Skiatook, in September?

 

I didn't bother getting internet service hooked up when I moved, more than 3 years ago. I tried using my phone, but way too complicated, and too small to do much. I finally got internet service and a new computer in the last couple weeks.

As for Sept, probably, unless the date happens to conflict with something else.

 

See whatchya get when you live in the sticks?

 

I'm not in the sticks. It's a tiny hick-town. Cable internet is available, since the school house is literally a stone's throw away..