I just replaced both the fwd tank and fuel tank selector switch on the dash. after maybe 100 miles after the switch replacement and 600 after the fwd tank replacement fuel began to overfill in the front tank.

I am rereading a similar post, several actually of this issue in the gas versions of these trucks. I may be wrong but i am understanding that our fuel system is quite different in the diesels. Plese correct me if I am wrong. I am just now learning this model trucks issues.

The diesel in tank sending unit has no pump. it is only a sending unit or a suction , valve, and fuel level guage correct? the primary pump is the mechanical lift pump in the engine bay which transports fuel to the rails.

what causes the rear tank to fill the fwd tank? and why would selecting the fwd tank still suck out of the rear?

Cost effective long term solutions to simplify the system and possibly improve it?

 

The transfer valve must not be fully changing tanks or the valve is damaged in some way. Yours thoughts on the fuel pump are correct. There are no in tank pumps.

 

As Ben said the tank selector valve is no completing the switch from one tank to the other. The valve is located in the drivers side frame rail.
https://www.ebay.com/itm/6-Port-Fuel...kmKz:rk:2:pf:0 This is what you need. Quite a bit cheaper than an OEM one.
https://www.ebay.com/itm/OEM-NEW-6-P...ZG7C:rk:6:pf:0

 

I say it is worth it to get an OEM. It lasted 20 years on the original, might as well put a quality replacement in there.

 

Much appreciated guys! Ill give that a shot. i had been reading about a spring loaded valve in the return lines located on the sending units in the tanks. Is that only for the Gassers?

 

No spring loaded valve on the return line just a rubber tip on the end of the return in the tank. It reminds me of the outlet on a "whoopee cushion". You could try removing all fuel lines from the selector valve and blowing threw the valve with compressed air from the lines that run to the engine, then switch positions on the in cab switch, and do it again. My 96 crew cab had a valve stick, and I replaced it with one from a parts truck. I tried the air deal, and I heard a slight pop, then the valve would switch positions when the switch was flipped. I don't know if it "cured" it or not as the one from the parts truck is still working.

 

From my experience you selector valve is stuck in the middle. Drawing from rear tank and returning to the front. My valve stuck or plugged in some way and the truck stalled and left me stranded. I replaced with an OEM valve, they are pricy but you don't have to cut and splice on a new connector. And as stated previously the OEMs last 20+ years so why go with the knock off. A cheaper option had you not just replaced your front tank would be to go to a rear tank only and upgrade to a 38 gallon tank. Also check your fuel lines and make sure connections are correct and you didn't get a return line connected wrong.

 

I have gone through 3 used units. then put in a new unit and no more problems. I have a used unit if needed. I have not tested it but took it off a parts truck as a backup.

 

If a new one will last twenty years I'll be dead before its dead!

 

Glenn, we might not be dead but probably driving one of those 3 wheel carts up and down the street sidewalks, not diving into the 7.3 engine for repairs. Actually they are pretty cool looking as long a they don't tip over. Think I have a few months on you on age wise so that makes me your senior, lol. We are both old compared to some of the young bucks on here. They all amaze me on their DIY skill sets and can do attitudes.

 

Tell you what Jim, lets get into the same old folks home and we can mod those carts to perform better. lol My father-in-law had one of those three wheel carts and nobody wanted him to ride it because they thought it was unsafe. I jumped on it and went in circles with it and I was impressed that they were pretty stable!

 

Im in with you in that

 

I Agree. I had the same Problem. One fuel selector valve later and the problem was fixed.

 

are replacements different?
Mine looks nothing like those in the links.

 

Mine looks like the links on my 97.

It might look different on the rail since it's covered with everything going on down there.