ok guys i have a problem i would like to figure out with my 6.9L 1986 F350 and hopefully somebody unfortunately had this too but i didnt find anything i thought was relevant searching. long story short this truck had sat for 12 years in a building. i have replaced every rubber item on this truck from front to rear literally. only when it has sat for about an hour since it ran last sometimes it will not fire up. its still warm and glow plugs arent needed but i have replaced them last week and i have a pushbutton and try them for a few seconds just to see but still no fire at all. i checked the FSS and have power and it clicks when operated. i also pulled the schrader and put a clear line on it to a bottle and cranked it over and its pumping fuel very well. i see no residue at all under the IP so its not leaking. no fuel leaks at any injectors or anywhere for that matter. it never does this when its cold just after an hour or so since it ran last and is still warm. now it does eventually start after cranking for a bit letting the starter cool down a bit but if i had to hold it till it started i would say it would take about a minute to a minute thirty seconds. when it does starts it acts like it has air in it and then smooths out after 5 seconds or so then is fine. now this doesnt happen every time. since i bought the truck last fall it has done it about 5 times. i just would like to track this sucker down and fix it so it doesnt leave me stranded when it doesnt start. the water seperator was changed out for a new style napa head and water seperator as well and this was done a while back. i rechecked it as well. i have checked everything i can think of and am scratching my head now. anybody have an ideas where i should go next??
and sorry for the long post i tried to keep it simple

 

My first guess is either the starter is cranking to slow or the IP is on it's last legs.

 

i wish it was cranking to slow, the batteries are brand new and the best i could get. she spins fine. i would hate to think the IP has gone bad from sitting ? maybe rust or other containment's from sitting that long in that IP ? if there were some moisture in the ip when it was shut off in 1996 ? i would think it would be giving alot more problems then it has but i don't know ? the rig runs like a champ and will for weeks on end then when you don't expect it..bamm no start, then it will go for a few weeks again.

 

If my 6.9 sat for an hour it would need glow plugs to start. However it does sound like you have fuel drainback. but only sometimes. Was the water seperator bypassed with a short length of rigid pipe? If so you could try replacing the rigid pipe with a non-return valve (aka one way valve). Only a few $ and well worth a try. This would prevent fuel draining back to the tank if there is an intermitant air leak.

 

I agree about the fuel drain back problem. There is supposed to be a check valve on the fuel return line at the filter head that prevents this but if its not working properly, its possible that fuel is suphoning out of the filter and IP. A quick way to test if this is your problem is to disconnect the return line from the filter head and plug the fitting on the filter head as well as the now loose return line. (the return line that connects the fuel filter head to the closest fuel injector)

Try that and see if it makes a difference.

 

this fuel drain back issue makes sense to me too, but i didn't think it was possible. i will try the steps you guys have mentioned. or maybe just get a new filter head ? thanks for the input.

 

Well, try the method I mentioned first to see if that is in fact your problem. The only thing you would really have to replace is one or two check valves. There are supposed to be two in fact, one on the return line at the filter head, an one on the injector pump return. It could be as simple as a small piece of crud in one of them that is preventing the valve from sealing properly. Or the rubber could be rotted out, which is not out of line if its been sitting for 12 years.

If the OEM water separator is still in use, than that could be causing you problems too. They are well known for leaking air into the fuel system. You can test this by temporarily bypassing the water separator with a piece of 3/8" metal pipe.

 

david ill check those check valves and do your method. it makes sense to me just hard to replicate the problem. i took OEM water seperator off when i read about the problems here and (this forum is great for information, you guys rock !!) i installed a spin on head and spin on water separator from napa in the original location. the rubber being rotted is a key point, everything on this truck that was rubber was shot and i know i didn't get everything but i tried