1986 F250 w/6.9 non turbo. Changed fuel filter and once started it ran as usual, then would not start without serious cranking or either. It seems to be losing prime, if in fact that is something these engines need. I am a newbie but am learning. Have changed all the return lines, the OE water separator was bypassed with a primer bulb prior to me purchasing the truck and was replaced with fuel filter that has a screw on water separator on its bottom. There is no fuel moving at any great value in the return lines. Even when engine is running, pulled return line off of injector plastic housing and no fuel coming out. Took off return line from IP and just a small flow from there. Opened fuel line to injector on one side then the other in hopes of purging air in system, fuel spurted out and then was tightened with still no starting with out serious help. Put a pressure test on the high side of the fuel line at the fuel filter housing and pressure was a steady 3.25 lbs at idle. Didn't run a pressure test on the return side since no fuel was moving thru the clear return lines. None of these problems existed prior to changing the fuel filter. I am going bald here trying to track down this goblin, any help is very greatly appreciated.

 

it sounds like your mechanical fuel pump is dying.
what is your fuel flow rate out of the filter when cranking?
remove the core from the schrader valve at the top of the filter, attach a hose to it, and crank the truck over catching the fuel into a container. you should get 1/3 pint of fuel pumped in 10 seconds of cranking.

 

Thank you TJC. It is a little off of what you said. I pumped 1.82 ounces in 10 seconds. 2.66 ounces equals 1/3 cup so I am about 1 ounce off which doesn't seem to be a lot but lift pumps aren't that expensive so I will change it. Is there anything else I should check that may be causing my problems?

 

well the other possibility is that the pickup tube in the fuel tank is cracked and you are sucking air.
that is another common problem with these trucks. they usually crack rite at about the 1/4 tank mark. if you are rite around 1/4 tank of fuel, try adding some fuel and see if it still does it.

 

Will do. how much volume of fuel should I see in the return lines. A friend of mine has an 87 F250 w/same engine but his return lines are full and when one return line is removed there is quite a bit of fuel coming out of the barb at the top of the injector for the return. Should mine be flowing like his or does it really matter about the return volume flow.

 

i never checked flow out of the return lines, all i know about them is that when the o rings go bad, they leak fuel all over my engine when it is running, and let air into the system draining my fuel filter back to the tank when it is not running.

 

Thank you for the guidance. The top of my engine is wet right now from all of the hose replacing and running down this problem. I will however check to see if the O rings are leaking after I get everything dried. Its just really weird that all of this happened after I replaced the fuel filter, before the filter change she ran good to the best of my diesel knowledge. Thanks for all the help, hopefully I will track down this gremlin with your suggestions. In replacing the lift pump, would you go mechanical or electric.

 

the original mechanical pump lasted 200,000 miles, the second one has been on the truck for 300,000 miles. i put an electric pump on least year to help fill the fuel filter when changing it and to use for starting after sitting for a while. the mechanical pump is fine.

 

Back to your original statement of - after you replaced fuel filter it took a lot of cranking. I am wondering if the seal for the filter is leaking air in and no fuel out as fuel is thicker than air. We have this problem with fuel return lines from injectors.

 

I was wondering the same thing so I removed filter and redone everything and lubricated seal again but to no avail. Still the same gremlin. The truck was running fine and it still does after I get it started but A friend of mine, who just bought his truck a few months ago, is a year newer F250 with the same engine was wired different then mine as to the routing of his fuel lines. His truck has a line running from the nipple/barb on the high side after the filter down to the return side on the injector just below the fuel filter. My truck just had some rubber ends over each of these barbs. Even though mine was running just fine without this route I figured, what the hell, So I ran a line the same way but that didnt change anything but it was a shot in the dark.

If the lift pump is going bad, would it let air in or let the fuel return back to the tank so that the system loses prime?

 

One thought... check all fuel lines for rust as rust will let air into the system letting the fuel to return to the tank. Yes the fuel pump could do the same thing. If I remember the fuel pump was $30 - fuel lines not available. I used brake line

 

Yes, There is some slight rust around some of the fuel lines going to the injectors and the return line from the IP. I was also thinking of doing the same thing as TJC did by placing an electric pump between the tank and mechanical lift pump. One of the previous owners bypassed the factory water separator for a filter w/water separator. In place of the OE water separator they put a primer bulb, such as you would see in a small outboard boat. Not sure what their reasoning behind that was as when I used it, it didnt change anything with my problem. There is no fuel around it so I dont believe its sucking air but it could be.

This is almost as bad as tracking down an electrical problem.

 

Yes it is frustrating. But you will get it done right. Just don't try short cuts as it might bite you in the end. Just think methodically. And keep your cool.

 

removing the line that goes between the filter head and the injector below it was a ford quick fix back in the 80's for air intrusion. mine has been eliminated since 1989.
when putting an electric fuel pump in,use a diaphragm pump and put it between the mechanical pump and the filter. this way the mechanical pump will do 90% of the work, and the electric pump will only work when it senses low pressure.

 

You bet, No hurry here just cant wait till I get the problem fixed. I am determined.