after about 20 minutes on the front tank the engines will start to sputter and sometimes it is preceded by a slight RPM increase. I switch to rear tank and it clears up. the other day drove it for 40 minutes on rear tank and no sputter. Tanks are more than 1/2 full. has a rebuilt high pressure pump with less than 500 miles on it. Starts fast. Any Idea where I should start looking?
Thanks

 

slight rpm increase and then sputtering is a sign of running out of fuel.
you most likely have a cracked pickup tube in the front tank.

 

Would that be the fuel sender system?

 

yes. the sending unit is attached to the pickup tube.

 

ok sending unit is out the black filter on the bottom is coming apart. found this part number
Fuel Filter - Ford (E5TZ-9J306-BA) says it will fit a F250 with a diesel engine but only goes back as far as 2003. part looks like this https://d354nuoz4t18d4.cloudfront.n...images/products/e5tz9j306ba.jpg?cb=1568553244 Do you think it is the correct one?
Thanks

 

probably not. most guys just replace the "foot" with a piece of diesel rated rubber hose cut a hair short of touching the bottom of the tank, with a "V" notch cut in the bottom of the hose.

 

what is the that red rubber valve on the side of the strainer for?

 

no idea. that is most likely for a 6.0 truck, and i have never messed with a 6.0 truck except to drag them onto the low boy to take for repair.

 

E5TZ is a 1985 truck part number prefix, so how the hell could it go back only as far as 2003?

Plus, this is an invalid part number, there is no 9J306 listed in the 1980/89 truck parts catalog.

The fuel tank selector valve used in 1983/86 E250/350 & F250/350 6.9L diesel has been a notorious POS since day one!

 

I am not having problems with the fuel tank selector valve. Is the fuel gauge sender and pickup that are the problems. The plastic filters at the bottom of both are soft and cracking. when running on the front tank, the engine starts to run out of fuel and the tank is almost full. I have a new front tank sender/ fuel pickup. but it reads off the full scale. I took it back out and tested it and it works fine except when moved to full side the gauge reads above the F. I am guessing if I bend the float rod , I can get it to read something less than full. The back tank is almost full but the sender only shows 1/4 tank. I will try cleaning it with a carb cleaner or brake cleaner which now works better the carb cleaner. will test today and see what happens.