This is EXACTLY what has been happening to me off and on for what seems like ever. I am going to drop tank this weekend and see what i find, as se der and fuel pickup assy. is about the last thing that could be wrong, everything else has been replaced in the last 2 yrs

OKAY! The first one to find a fix for this wins!

in all likelihood, there is some sort of air leak inside the reservoir where the black color coiled pickup tube is located. I've replaced the reservoir with another 25 year old unit, and the truck stumbles but doesn't die out completely. Thia was with 1/4 left in the tank according to the gauge. Since then I keep it full and no less than half tank. The issue has not returned....yet. My goal will be to replace,the pickup tube in the future.

Does this tube you speak of follow a floating fuel pickup? Is that why it develops leaks? I have tried pressurizing my tank also to no avail. I'm going to try again this spring and put a gauge on it to see that I don't go over 5 psi. Before I only had the crappy gauge on the compressor which is hard to see when the pressure is that low and I didn't want to blow the tank up. When I had the bad off I replaced all of the rubber hoses to the tank including the fill pipe so I don't think it's leaking there. I don't see anything at the hose which goes to the engine fuel pump either.

Just like yours, mine acts like it has no fuel on starting if it gets down towards 1/2 tank.

Edwin

Update:

I am guessing that I must have a plugged tank vent causing my issues. When I put my flatbed on, I have been doing the same dance as many trying to find a good route for the filler neck without having to block the bed up so high so I just bungee my filler neck to the frame rail. What looks like to me is that the only place I was getting Tank venting was through the filler neck vent tube. I was chasing leaks everywhere else I'm assuming because like Oliver said my vacuum was finding weak links someplace else so I was chasing Gremlins everywhere but where the problem was. I found a long spring in the back of the shop on a Shelf the same diameter as the inside of that vent hose and cut it to the length I need and fed it down that hose and have not had a problem in 4 days. Going to drop the sending unit today and see what I find in the top of that Tower but I think I am on the right track don't know if that helps you or not but I'm seeing some light possibly for the first time in a while

And just to clarify I'm not saying you need to shove a spring down your filler neck vent tube, I'm getting at that venting system in the tank causing the vacuum it's probably both if not all three of our issues in some way shape or form and we've been trying to put out the fire by dragging the furniture out of the room instead of dumping a bucket of water on what's burning

Thanks for the idea. I'll look at that sending unit vent the next time I open er up.

What do I win?

I have fixed this problem on two of my trucks over the past few years. Poncho [my '91.0] and the Blue Donkey [my '95] both had this problem.
Poncho would do it only occasionally when the tank was running low.
The Blue Donkey only did it when the temps got -15F or below and the rubber fuel line[s] got stiff and allowed air to seep in, rather than the thick cold diesel fuel. Nothing quite like fiddling with your truck in the -20F temps on the side of the road.

The problem lies between the motor and the fuel tank. If need be change the lines, clamps and be done with the problem. I didn't need to change the in tank sending unit, but it is a potential culprit as T-man has found out.

Both my trucks where fixed with a complete replacement of fuel line from the motor to the fuel tank. I also install a HVLP lift pump on Poncho at the same time as I wanted to upgrade from the standard diaphragm lift pump.

Our enduring gratitude?...Mark

I've collected a sack of those over the years...Unfortunately the bank and I still can't agree on their cash value...:2cents:...Ben

Roughly equal to one Attaboy. If you collect 50 Attaboys you can redeem them at my house for 1 cup of decaf. Caffiene is extra.

Note: One Aw Shucks cancels out your account and you have to start all over.

Edwin

Drat!...Oops!...:doh:...Ben

Hey Folks

Hey Edwin Smith, since this pertains to you and your rig too.

I think I finally got a hold on the air infiltration issue that's plagued me for so long. Keeping the fuel tank full was a bit of a bandaid approach, so I decided to delve deeper.

The only time this truck broke down (the several dozen times over the last decade), was when the fuel tank was 1/2 tank or less. That got me thinking again on what I should do to fix it. I do believe I was on the right track all along, but since I did the most recent repair, it's been good even letting the fuel level drop to "E". Granted there's still 6 or 7 gallons left at "E", but it still would have left me stranded on the side of the road in most cases.

So I took the reservoir out and inspected it. The fuel reservoir metal assembly bracket was cracked, but that's not related to this. Luckily, I had an extra reservoir from Ollie, and was able to combine the two reservoirs into one.

If you look at the attached photos, you will see what O rings that went bad in the pickup tube from the reservoir bottom. They were both shot after 30 years submersed in fuel Mushy and did not have a tight seal on the brass pickup tube in the reservior head.

You should take photos of every step, as this system is oriented in a specific manner, and you can easily disassemble and reassemble without putting it back together in the same clocked orientation. If you do, the tube will not meet the reservior head and brass pickup tube in the correct spot.


Time will tell, but I'm really sure that these two soft rings were shot, as when I put the new rings in the pickup tube, and assembled it, it was tight, vs the old which was loose and wobbly.

I would NEVER buy another one of these reservior fuel filters that mount to the bottom of the reservoir. I put my original red bucket screen back on there, as this piece of garbage fuel filter allowed all the junk to bypass it.

https://cimg2.ibsrv.net/gimg/www.die...b371e376a9.jpg
Bed cutout


https://cimg3.ibsrv.net/gimg/www.die...33a9685061.jpg
Removed from truck tank
https://cimg5.ibsrv.net/gimg/www.die...6695a7e2ce.jpg
Broken metal hanger on reservoir
https://cimg7.ibsrv.net/gimg/www.die...d14f1a27ae.jpg
Brass pickup tube and connector
https://cimg8.ibsrv.net/gimg/www.die...a294d8e669.jpg
O rings inside pickup tube
https://cimg9.ibsrv.net/gimg/www.die...18e2edb337.jpg
Orings removed
https://cimg0.ibsrv.net/gimg/www.die...056032680f.jpg
Clogged return fuel screen
https://cimg1.ibsrv.net/gimg/www.die...6e369d98f7.jpg
Cleaned screen
https://cimg5.ibsrv.net/gimg/www.die...af9efd3525.jpg
STOCK SUCK *** FILTER was FULL OF DEBRIS
https://cimg6.ibsrv.net/gimg/www.die...f413f9062f.jpg
Harbor Freight for under $10.00

😁...

Before we moved to Oklahoma we bought a 5th wheel trailer to live in for 9 months because we sold our house before the wife retired. Because I am still having the fuel problem in desperation I installed a rubber line from the tank all the way to the lift pump. It didn't fix the problem so it MUST either be in the tank or the lift pump is shot. Since it's a fairly new piston type I'm pretty sure it's a problem in the fuel tank. I have cut the hole in the bed floor and made it into a cover with screws. I pulled out the pickup strainer float assembly. I replaced the rubber line and I inspected the whole thing for leaks. I don't see the o-rings you showed but I'll look again. I need to drill out the holes which hold the rubber line nipple to the top assembly since one of them seems to be stripping out. I can put a screw and nut in there to hold it more securely. There are a couple of rubber gaskets under there but they were soft and pliable. Could still be leaking though. The strainer is probably in need of cleaning again.

I haven't done anything here in Olahoma because we've spent the last year fixing up the house and garage. Since it's cooled off some in the fall I'm about ready to do some more repairs. A few things have accumulated that need attention. I still haven't installed my D.E. 4 inch exhaust system.

Edwin