Cautiously optimistic that you are right. After putting the charged batteries back in and a fair bit of cranking, it started off the rear tank. It's idling fine and I was able to move around the yard without issue. Rear tank shows 1/4 so... not sure why it showed 1/2 two nights ago. In any case I'm going to grab another 5 gallons of diesel and put it in and then do some driving, see if it will cut out on me again. Actions items are to drop the front tank and do whatever I need to do to fix the sender, pickup cone, clean the tank, whatever. Then I'll do the same with the rear so all of that is new. Then I'll come back around to the injection pump and possibly redoing the injectors again, since the ones you get from Pensacola Diesel seem to be of dubious quality. After that, alternator, red top steering box, all new rubber front and back, new shocks, new weather seals all the way around, etc. If the rear tank is ok I should be able to cruise around for now and fix it up as I go along.

 

The sending units when old can be unreliable. Stick to a single tank operation until you know for sure your tank switch valve isn't stuck and is transferring fuel from one tank to another.

 

The valve is brand new as I installed it a few days ago. 2nd valve already for this truck... if anyone knows of a quality brand for that selector valve I'm all ears. I can verify I hear the zip noise of the valve operating and I do see the tank level change when I hit the switch on the dash. That being said, the front tank sender sends the needle to the moon so after all that has happened I'm going to posit that sender is busted. I'll be staying on the rear tank until I go through the front tank and make sure it's 100% operational.

 

If you still have the original valve it might be the best one. If it was stuck it was probably from not being switched back and forth every tank use. Like some just leave it on the front. Eventually it's stuck there. Probably the original only needed a cleaning if non use was the reason for sticking.

 

I do not have the original valve. I think the valve I found was a Dorman, and it buzzed constantly when you tried to switch tanks. I replaced it with another Dorman as that's all I could find. A few days ago as I was working with everyone here about the truck I noticed I wasn't switching tanks anymore and found the selector valve fuse was blown and the valve itself ohm'd out like it was stuck on the front tank. I replaced the fuse and replaced the valve under warranty, which brings us to the currently installed valve, which is working... for now.

 

I think the original valve defaulted to the rear tank. The valve would switch to front when the switch called for it. Which makes me think that when left on front everytime you turn off the key it switches back to the rear, exercising the valve. So maybe the worst thing is leaving it on the rear too much? Might be different for years above 86 as I think they switched the operation of the senders and guages. You have to stay year specific on the senders. As for aftermarket valves, there have been many complaints and issues. Some have gone to a manual marine type valve for the plumbing. You can still use the switch for the sender or use your trip odometer to keep track of mileage.

 

As long as your odometer works you can always drive by mileage. I haven't had a functioning fuel gauge or trip odometer for over a decade now and I've never ran out of fuel. I just keep a pen and small pad of paper and note the mileage when I fill up, and as a bonus this allows you to track your overall efficiency.

 

The wife may need to drive this someday in a pinch which means everything has to just work. The truck took me and my son to town and back without issue today on the rear tank, which was nice. Rear tank sender is mostly borked though. I filled the tank until it was overfull and up to the cap and it still only read a little over 1/4 a tank. So new senders and cones of shame for front and rear tank. Pulling the tanks will also give me a chance to inspect them and clean them if needed.

I also do run an automotive youtube channel, so replacing the senders and pickups is worthy to film and put out there so others can learn from my mistakes and bring their truck back, or keep it on the road a bit longer.

 

I know what you mean about "everything has to just work". Years ago I broke down far from home and had to go to a shop and the first thing I said was disregard all the gauges and trust me I have plenty of fuel. When I dropped my rear tank many years ago it had the toughest algae-type growth on the bottom--maybe the PO ran bio-diesel? No amount of scrubbing, scraping, or swearing would budge the stuff and I needed the truck the next day for work so had to leave it that way, but it's been fine for many years. I figure a pressure washer would have been the ticket or a long soak in something strong.

 

More updates on the fueling system. I dropped the rear tank and learned some things. Firstly that someone replaced the rear tank with a plastic one. Appears to be the right plastic tank so good there. Also looked like a more recentish sender was installed and I think it was working correctly. It did appear however to have been installed without the pickup cone because it wasn't there and I didn't find it rolling around in the tank. Filler neck is not OEM, that was replaced in 2016 if the date code on it is to be believed Roll over valve seems original but ok, vent line is clear. Now the weird stuff. I'm finding that when I get the rear tank to around 1/4 full, the filler neck backs up. I had the filler neck apart to make sure the interior flexi hose was fine and it is. Pondering over it more, I think the exterior rubber hose is collapsing where it goes over the frame rail.

When the tank is empty, the fuel level is below the filler neck opening in the tank so displacement can still happen along the bottom of the filler neck and it fills just fine. However, once you get to around a 1/4 a tank, the bottom of the rubber hose now has fuel in it and because the top part of the rubber hose is collapsed, displacement can't happen anymore and it backs up. I noticed there's a metal shield that was attached to the rubber hose that I thought was there to be an abrasion shield against the frame rail... thinking more it might also be there to give support to the rubber hose to prevent it collapsing.

I'm going to see if I can massage the exterior hose around the frame rail to open it up a bit to verify my theory. If so I guess it's drop the tank again and come up with a way to open up the exterior rubber hose and keep it open during reinstallation of the tank. Did I mention I did all of this with the bed on? It's a giant pita to do rear tank work with the bed still in place.

 

on my 88 and 89 trucks, i could only put fuel in on the lowest nozzle setting. and sometimes it would still back up and spill out.
but drive the driver side rear tire up on a chunk of 6X6 and it would take fuel as fast as you could put it in.

 

If the rear tank was replaced, very easy to get the filler neck on in the wrong orientation making it kink over the frame rail. A replacement filler hose makes getting over the rail more troublesome especially if not OEM. Proper hose in the proper orientation should fill fine. I always fill on the slowest speed regardless of any tendency to shut off. It's just safer when the auto nozzle sticks, and they do often.

 

I'm wondering if it's possible for me to insert a spring in there like it's sometimes found with radiator hoses to prevent the rubber hose from collapsing. For now I'm waiting on the sender unit for the front tank so I can drop and service it. Then servicing the driveshaft, then running the truck to get the rear tank near empty then I'll mess with it again.

 

There's no need for that. The filler tube is far too strong to collapse on its own. A spring wouldn't do anything (in fact, it would probably slow flow down some, if not a lot). If you want to fill faster, install a larger vent tube/fitting on top of the tank. That will allow you to dump it in on full, using a big rig truck nozzle. After a few gallons, both of my 9th gen trucks can take the big nozzle (90% of the time) clicked on full (or very close to it), so they used a pretty nice size vent this era. I guess the 7th and 8th gens (pre '92 idi trucks) probably got smaller vents, cus I don't hear about this issue with the '92+ trucks.

 

No spring. You're going to crowd the vent tube. The routing should be kink free. If your hose is kinked it's wrong. Filler neck supply is one source for filler hose. No rear tank filler hose available but they do have pieces and fittings you could mimic the original.

I reused my filler hose when I replaced my rear tank. I made the mistake of not marking the orientation when I removed mine. I put it on wrong but didn't notice till the tank was up. I was able to loosen hose clamps and rotate the hose to the proper across the frame rail orientation. Bingo, no more kink. A strap wrench came in handy for that.