I've got a leaking fuel line somewhere on my '91 - it's never been replaced and I'd like to replace the whole thing for good measure. Does anyone know of decent DIY article specific to this engine, or a decent book? If not, what are the lines that typically need replacing on this engine?

bart

 

is it your return lines or supply lines ? do you have a single or dual fuel tanks ? do you know or can you see where the fuel is leaking from ? any info you can provide would help us help you.

 

I recently replaced all my fuel lines...3/8" for supply, 5/16" for return...used hose clamps, where needed...works good and will probably last a long time. From both tanks to the fuel tank sw. From the sw to the elec. [add-on] fuel pump. From the pump to the fuel filter. From the return line to the sel sw.

 

I believe it's my supply lines. It's seems to happen most when it's cold. What happens is the engine starts right up, runs for a couple of seconds, and then dies. After significant cranks it starts up again. I assume that the fuel lines are priming during the cranks. I have dual tanks, but the one tank is no longer install because it rusted out. I have a replacement waiting to go in once I figure out the fuel line issue. I'm not sure where the actual leak is. I don't see any drips, nor do I smell any fuel. There's the fuel line that goes to the injectors that my mechanic put a clear hose to show me the air in the fuel line. He had just replace the glow plugs and all was working well enough at the shop (which is heated). But on the first cold day after it came back from the shop I had a hard time starting again. So, it seems like a seal somewhere is letting air in the lines. Any ideas?

bart

 

Hay Bart, i have a
1988 F250
7.3L Diesel
4x4
Super Cab
XLT Lariat
with the same problem as yours. Has anyone given you an idea of what the problem is?

Glen

 

each tank has a 3/8" line going to the selector valve (located on the driver's side frame rail just in front of the front tank). this line is hard plastic with o-rings in the fittings.

there is a 3/8" line going from the selectror valve to the lift pump (located on the lower front pass side of the engine.) this line is made up of hard plastic, steel, and a section of rubber line at the lift pump.

there is also a section of hard steel line going from the lift pump to the fuel filter housing. this section genearlly does not cause a problem if the fitting are good and tight.

you could be sucking air at any point. bad o-rings, rusted pin holes in the steel line, or a weak rubber line at the lift pump. you could also be sucking air if the selector valve is not shutting off the input from your bad tank. since this is not under pressure, you could suck air without ever seeing a fuel leak.

any and all of these fuel line sections can be replaced with standard 3/8" fuel line hose. it does not have to be the hi pressure stuff used for gasser fuel injection. if you are not going to be replacing the bad tank for awhile, you can bypass the selector valve for now and go straight from the tank to the lift pump. that will eliminate a possible bad valve.

the 5/16" lines are the fuel return lines. they can be replaced with 5/16" rubber fuel line also if you take the replacement approach. the return starts at a "t" connector at the top rear driver's side of the engine, and follows a similar path back to the tanks.

hope this helps.

 

One thing.... How are the injector return lines. Are they painted gray? If so there is the problem. Hairline cracks form in old rubber hoses. They will let air in but not leak fuel out. The hoses will be brittle if old.

 

same exact problem on my 83 i replaced all my return lines, dropped my tank and drained it thinking I had bad fuel, I think next is going to be the supply lines. Can you use braided steel lines or does it have to be rubber?

 

i got i think kind of the same problem. only didn't think about the selector valve. dropped the rear tank off truck to replace it and haven't got it back on yet. even though i kind of sort of sealed the ends of the lines to the sending unit, they swinging free in the air. could this be my problem of sucking air as well?
speedrdr

 

braided steel lines can be used, but that is a huge overkill. understand that this lines are NOT under pressure. the lift pump sucks fuel from the tanks via the selector valve.

the return lines to the tanks have more pressure than the supply line and it is only a few psi.

----bigredtruckmi---i agree that the injector return lines may need replacing, but if he is seeing bubbles in the supply side, he must be sucking air.

 

I'd bet on the return lines and/or o-rings. Start-up then die after sitting a long time, is a classic symptom of return line leaks. When you replace the glow plugs, it's tough to not disturb at least one these lines, especially if you don't know not too. If you got old lines, just bumping one can create a leak big enough to let air in, but not fuel out. You can get kit for under $35, I believe.

 

jus thought braided steel would last longer.

 

wow - thanks guys! There's a lot of good info here. I'll dig into the truck tonight (if the weather holds up) and start adding things up - it seems like replacing all the supply and return lines, as well as any o-rings is a safe bet. It may be a little overkill, but once it's done I'll have the piece of mind knowing its done. I'll post back with any questions and pics!

 

I had the same problem develop on my 86 after it ran out of fuel on a hillside. There is a check valve in the fitting where the return line comes up to the fuel filter housing. If it is still connected to it, take the line off, plug it, and cap off the fitting on the filter housing and see if that solves your problem. IH actually put out a tech bulletin from what I have been told about doing that. The line does not need to be there to operate properly. But also, the return lines themselves can cause it. What happens is the fuel drains back to the tank, syphoning off fuel from the filter, and leaving you an air pocket, which the IP sucks from, and you essentially run out of fuel. If it runs fine after getting it restarted, then it is either the check valve (most common) or return lines/o-rings (2nd most common) Trust me, if it was supply side, it would be more troubling than a little extra cranking, just got done chasing all the air leaks and other problems on my 92... shut the truck down and cost me 2 1/2 days of messing around to get it straightened out.

 

One more thing. The pickup tubes in the fuel tanks are known to crack or come off. When you get down to about 1/4 to 1/3 tank, you can actually run out of fuel. On my truck, if I leave it parked facing even a little uphill while switched to the front tank at about 1/3 full, it will suck air...it'll run fine down to less than 1/4 tank, but will start and then die with less than 1/3 after sitting a while.