I’ve got no fuel pressure and no fuel pumping into the bowl. I’ve taken the fuel filter out. Had it cranked over by a friend to see if the ball was filling up and it’s not, so then I thought fuel pump, so I ran a fuel line from the inlet side of the fuel pump, straight to a 5 gallon jug of fuel, and then it pumps fuel like it should. So now I’m thinking selector valve is stuck on rear tank, as I was driving the other day and when I started off I had a quarter tank of fuel then the gauge moved up and was showing half a tank then the truck was acting like it was about to run out of fuel so I switched to the front tank which is full but it won’t pull any fuel from the front tank now. Before it was switching back and forth fine both tanks work, could the selector Valve be stuck on the empty rear tank and not switching to the front? It’s also reading the front tank which is full but if I select the rear nothing happens it doesn’t read the rear tank now. I checked for power going to the valve and it’s getting power but I don’t think it’s working properly. Any ideas I’m kind of scratching my head now. I’ve also eliminated the rear tank and I am only running on the front tank now as I suspect the rear tank may be rusty, but I’m not running through the selector valve and I’m still not pulling fuel from the front tank even though I’ve bypassed the selector valve

 

Sounds like could be pick up in the tank. You eliminated most everything else.

 

Fuel starvation around 1/4 tank seems to be the typical symptom of the in-tank "showerhead" pickup breaking off. But switching to the other, full tank should remedy the issue. Gage needle jumping combined with not pulling fuel from full tank suggests the selector valve may be bad, or possibly jammed with debris from the rear tank. The "showerhead" also is a coarse filter, so you could have sucked up gunk or debris once it broke off, then jammed the valve, preventing it from switching tanks. Sorry, I don't know if the valve can be cleaned. Running from a fuel can suggests pump and lines are OK.

Your situation sounds like a tank showerhead broke off, AND the selector valve is jammed on that tank. But don't be too certain which tank the valve is actually stuck on. My valve failed one tank switch prior to when I thought it tailed, so the tank I thought I had run empty and was stuck on actually was full and the valve was stuck on the other tank that I thought was full, which was actually empty. I added a can of diesel to the tank I thought was empty and being pulled from, but was actually full and wasn't being pulled from, so I overfilled it. Run to a station for another 5 gallons, put it in other tank, and got home.

I'm curious about how you bypassed the selector valve to pull from front tank. Do you know you have a good seal on both suction and return lines, AND that you connected suction to suction and return to return? I would think that straight plumbed into the front tank should work. Are you sure the front tank is above 1/4? Might be worth putting 5 gallons in it and see what happens.

If one showerhead went and one tank is rusty, the other set likely isn't far behind. When I replaced my pickup/sending units and tanks, I also replaced the connectors on the lines to the pickup/sending units.

My $0.02. Some advice is worth less than what you pay for it.

 

Turns out your right on the shower head being broke off but also what was supposed to be a full tank of fuel ended up being empty, only explanation is a thief in my area because I know for certain the front tank had fuel in it I had just filled both rear and front tanks up. But the weird thing is the gauge was showing that the front tank was full. With knowing 100% that I just filled it up and the gauge showing full why would I check. I decided to check just for the heck of it and wanted to check the shower head so I dropped the tank and pulled the sending unit and that’s what I found. I made sure the source line and return lines were hooked correctly and to bypass the valve I just unhooked the lines from the valve and connected them together, so it’s running straight from the tank to the pump no valve or anything in between.

 

Sounds like you filled up both tanks, and drove only enough mileage for about 3/4 of one tank. Is the mileage you drove "about right" for using up 3/4 of a tank? If the selector valve is bad, gage readings may be off or wonky for one or both tanks. Depending on when the valve failed relative to the last time you switched tanks, truck could be pulling from the "other" tank rather than the one you think it is, plus the gage might not be going down like it should.

Sounds like you THOUGHT truck was pulling from rear tank, but I'm not clear on which tank you dropped.

Which tank did you drop and find empty with a broken-off showerhead? Have you checked how much fuel is in the "other" tank, independent of what the gage says? If you've only driven enough mileage since last fill for about 3/4 of a tank (say 150 to 200 miles), I would not be surprised if the "other" tank (the one you didn't drop) is near full. If you've driven more like 350 miles since last fill, both tanks could be low, either empty or below broken-off showerheads.

To me, mixup on which tank actually is being drawn from from and how many miles since last fill are more likely than a diesel thief. But if you're absolutely certain that you have very few miles since last fill, then a thief may be possible.

 

I filled both tanks 2 days before my problem happened and was running on the rear tank and on the 3rd day I had a little more than 1/4 of a tank on the rear and just driving along heading to work it started acting up and I noticed the fuel gauge was reading empty for the REAR tank. It was at that point yes starving for fuel and I switched it to the front and it stayed running for about 5 minutes then died just like it ran out of fuel. Wasn’t running the front tank at all only the rear the first few days I can run 2 and a half days on each tank getting 5 to almost 6 days worth before needing to refuel and I always fill both tanks at the same time, I drive this thing to work. Been driving this truck for several years now and I have always ran it like that, ‘ not completely empty btw’ I normally switch tanks when I’m down to a 1/4 of a tank.I’ll run both tanks down and then refuel at the same time. My front tank should have been full not empty I hadn’t been using it was only running the rear tank and when I ran the rear tank empty’ not meaning to’ I switched to the front and it should have been full and everything should’ve been fine. Also I did check the rear tank to be certain is was empty and it was

 

Hmmm... so mileage is appropriate for using about 3/4 of the REAR tank, and none of the FRONT tank, or vice-versa. However, FRONT tank was empty / near empty, and REAR tank was empty / near empty, so ONE tank of fuel went "somewhere". One of the tanks has a broken-off showerhead; this should result in fuel starvation at about 1/4 tank remaining, which was observed.

Since roughly one tank of fuel "disappeared", about 3/4 tank is expected usage, and the tank you dropped has a broken-off showerhead, is it possible that:

• Rear tank has a broken-off showerhead, resulting in fuel starvation at about 1/4 tank remaining,
• Front tank "lost" roughly a full tank, possibly stolen, and
• Tank selector valve is functional, issue is tanks are empty or below broken-off showerhead level?

It's also possible that the tank selector valve has failed, we don't know which tank it is pulling from, and the tank you didn't drop also has a broken-off showerhead.

If both tanks are empty or near-empty, I would strongly tempted to:

• Drop both tanks
• Replace both pickup/sender units... if one showerhead went, other is not far behind
• Inspect both tanks and if one is corroded, replace both
• Line-side connectors to the pickup/sender units are a good idea
• Replace selector valve. The quirky gage movement suggests it's having problems.

If you need to get it back in service quickly, try putting 5 gallons in the tank you think it is pulling from and see if it stays running. If so, fill that tank, and keep it above 1/4 until you fix things. If not, putt about 5 gallons in the "other" tank without switching tanks, and see if it runs (in case selector valve stuck on the "other" tank) Once you have a tank that works and is freshly filled, you can try putting 5 gallons or so in the other tank and see if the valve seems to switch and change levels on the gage. I would also be carrying a 5 gallon fuel can to put into the "trusted" tank if you get low and can't keep the truck running by switching to the other tank.

At this point, we can't condemn the selector valve. We really can't tell if the valve is functional or stuck, and if stuck, on which tank. Need to have one tank with adequate fuel, one tank known empty enough to starve for fuel. If it runs in one tank selection and starves in the other, valve is working. If starves in both selections, or runs in both selections, we know valve is bad.