1984 6.9L diesel quit. what the ?...

A while back I posted about the cherry 1984 F250 my boy and I got. 6.9L with only 27,000 actual. It was my farmer uncles and obviously sat a lot. We put about 500 mi on it. We've basically used every week or so to do a mowing job and kept it in the barn. I took it out last night to pick up a piece of furniture and low and behold it died. Got a ride home in roll-off. It ran out of fuel gradually like it was getting air. Just before it totally died I looked under and fuel was dripping at rear of engine off to the side, so I figured the rubber fuel line going to lift pump probably cracked due to age. Well after looking, its not so. The filter was full when I took it off so I believe the fuel supply and lift pump are working and the fuel appears to be leaking out of the inj. pump. I knew the seal around the advance was damp but in my experience which is with 6.2L Chevy's, I've never seen a pump just start leaking out and draw air. I've always seen them become hard starters beforehand. Its wet in the valley but would only fire and die so I never got a good leaking flow going again to see the actual leak.

The GM 6.2 pump is basically the same pump as the Ford IDI's. I'm sure you already checked all the rubber return lines, injector tee/hats and that return line at the back? I had a 7.3 IDI that started leaking at the center line at the pump (supply) I got lucky that it was just loose.

My guess is you have a piece of fuel line or other contaminant plunging the inlet to the pump. There are also rubber seals on the supply and return lines that tend to dry rot. I doubt the pump itself is a problem. There's a lot of difference between that an a 6.26.5 fuel system. I'd bet on a line seal coming apart. I would start by removing blowing out and resealing the lines from the filter to the pump.

If he used BIO FUEL and its been setting that much i'll bet everything is plugged up.

Yes, I guess I should have mentioned that all the little return lines are dry and all metal connections are too. I guess I have to wash off the pump and valley and try to track the exact leak.

The fuel return line on the 6.9 and 7.3 IDI engines have plastic caps that are on each injector with rubber hose in between each. They get brittle and crack I would say that's what's going on. IH Navistar truck dealer will have the parts much cheaper than Ford or you can buy a complete kit on line. You will need to disconnect the injector line from each injector to replace the return lines. Hope this helps need more just ask.

Check the water separator. Some times they will develop a leak and allow air into the system. Had it happen on two 1986 trucks.

You may need to look around for a guy who has a lot of experience with them. Boss had 1 that did just as yours did. Nobody local could get it to run. He called some friends at the largest ford dealer in Iowa. They recommended a young man, I never knew his name. Young man brought all kinds of equipment, took him 1/2 day to find a bad sensor. I had a 6.9 in a service truck. I spent more money on engines, glow plugs, water pumps, starters, torque converters, tranny's, and front end parts than any other service truck I ever owned. Good luck with yours.

The o rings under the plastic fuel return caps are probably bad. The short fuel lines will probably be damaged when you go to replace the o rings. It is recommend to install a complete fuel return kit. The caps should be reusable but they come in the kit...On High mileage engines, the o rings will wear groves into the caps.

also, the water separator ,located in the far drivers side corner of engine compartment, is known for developing air leaks. The plunger stem seal on top will leak and plunger seat at the bottom will leak.

Although they will leak as described I dont think the return lines will cause your issue. My son has a 92 7.3 IDI with only 52K miles and after you check it over thoroughly for air leaks and fuel pump problems here are some other things to check.
We constantly had troubles with the filter water separator leaking and thus causing air in the fuel problems until we junked the OEM type filter cartridge and bottom cap and replaced it with a one piece spin on filter that threads to the OEM base. This conversion element is available from NAPA. If local store cant find the part number I can get it for you. Even if this isnt your current issue it will be at some point and the conversion filter element works great. Since you have 6.2 GM experience you probably know this but a symptom of those rotory pumps going bad is exactly as you describe. The governor ring deteriorates and plugs the return fitting and when the case is pressurized the pump cant work. This may be why it starting leaking, probably out the timing window. If this is your issue the truck will start back up after a few minutes and act fine but soon loose power and die again.

I had an 86 with a 6.9 that sat a lot before I bought it - I had to change the fuel filter about every 500 miles for the first couple tanks.
Another thing that will make your life easier is to put an electric fuel pump down on your frame rail, and bypass the mechanical one. Diesel fuel would rather be pushed than pulled.
One more thought - I had another 6.9 that I fought with for a year with fuel starvation issues - it would work fine under light load, but if you put the pickle to it, it would starve. Turned out it was the tank selector valve.
Good luck - the body style of that vintage is still my favorite
Pete

Lots of things to check. The injection pumps until 1985 had a plastic weight-retainer ring inside the pump that falls apart. Same as many farm tractors have. It was eliminated in 1985 and all older pumps when repaired got updated. Kind of rare to find a 6.9 today that was not updated a long time ago. Pump shops used to put a metal tag on top of the pump to show it was updated. It might say "EID" on it. EID is the upgrade (Elastomer Insert Drive). Mechanical fuel pump also must be in good shape and is cheap to renew. It acts as an anti-drain-back valve. Also the Schrader-valve on the fuel-filter housing is subject to leaks. Then also what was already mentioned. New return fuel hoses and tees on top of the injectors.

Those injector pumps failed early if not upgraded. I did not think there were any left anywhere that were not updated years ago. But if it really has low miles and one owner as you say - maybe?

Mine died when I tried to leave an intersection one time. I had to wiggle the wire that goes to the front of the injection pump. A little corrosion I guess. It never did it again.