1991 F-250 7.3 IDI, I have a small leak on the fuel line (I assume the supply line) on my driver's side chassis rail, just underneath the cab. Do the return line and the supply line both run down the driver's side chassis rail? Is the supply line steel? I have not got under the truck yet to see exactly which line it is coming from but since the leak is constant I am assuming the supply line. I would like to just cut the damaged portion out and put a replacement section of rubber line in its place with some hose clamps. What size of rubber fuel hose would I need to fit over the existing supply line once I cut out the bad section? Thanks in advance

 

The fuel lines are plastic/nylon, not steel. You can't just cut out a section and use rubber hose. You need to make sure the plastic/nylon line has a hose barb installed in it.

 

If you are splicing the plastic fuel line, you will need some of these.
Local Auto Supply will have these in a 2 pack for around $10.


If you are going to use a Barb Fitting, you will have to get the plastic
warm enough to stretch over the Barb.
Do a Google search on how to install these things, lot of YT Vids on it.

Pushing a 3/8" rubber Hose over a 3/8" plastic line is difficult, even using
silicone spray, W/D-40 etc. Can only get it on maybe 1 inch or so, and
being smooth have doubts on how long it might hold w/o leaking.

Iam right now in the middle of ripping it all out because of the FSV pulling
from the rear tank and dumping into the front tank. Iam becoming an expert
on Plastic, Rubber, Barbs and Slices. GRRRR....

Charlie

 

So the stock plastic line is 3/8 inch nylon?

 

Oh ffs, do you ppl not realize the IDI supply lines are under VACUUM all the time??? There lift pump on the engine is SUCKING the bits in together, not trying to blow them apart under 40psi of pressure like a gasser in-tank pump will?

There is exactly zero issue slipping rubber hose onto plastic line, I got rubber hose coming right out of my TSV and into a massive pre-filter and then from the filter to Tyne plastic line in the frame, it's been like that for many years and ma y thousands of miles, no problems whatsoever. Just use stainless clamps cause the stuff the parts stores sells is junk and will rust in short order, but that's all there is to fixing these lines. On the return line it's the same idea, this one does actually have some pressure in it but it's minimal, and if the hose blowing off the line is a concern then just tie it to the brake line or the chassis harness and it ain't going nowhere, can't blow off if it can't snake its way away from where it lives.

Also, the IDIs actually DO have a steel fuel line, it starts on the driver-side frame rail and runs along the engine crossmember and then a bit along the passenger-side frame rail where it ends next to the lift pump.

 

Supply line from the tanks are 3/8" indeed. Return is 5/16" IIRC. As I said supply lines are under suction while engine is running, so you might get air in but there should be no fuel leaking out. Return lines are under low pressure, check the hose the drops down from the engine as it gets dry with age and fuel and sometimes starts to drip up where it's attached to union at the top back side of the engine, the fuel leak will then follow the hose and the plastic line till it meets a plastic clip at which point it will start dripping on the frame rail.

 

it will be the return line leaking.
the return line is under pressure......sorta.
if it was the supply line, the truck would not run because it would suck air through hole instead of fuel from the tank.