Ok so.. 1985 F250 6.9 diesel. almost 500,000 miles. Fred has ran great for so many years! All of a sudden, Fred acts like he is running out of fuel when driving if I let of the pedal and coast.
So I changed his fuel filter. Ran good for a couple days and then same thing. Starts fine, accelerates fine, then when I let my foot off to slow for a stop sign or turn or something, starts jerking back and forth like the tank is going dry and I have to pop him in neutral and rev him to keep him running.
So I put in a new electric fuel pump, and new sending unit in rear tank (front tank I never used because of similar problems, but have been using only rear tank for 2(ish) years now. Again, ran fine for a couple days, and NOW... same problem, except ANYTIME i try to drive him.
I start him up. Runs fine. Rev the engine, Runs fine. Put him in gear and by the time I get up to about 15 mph, he acts like he is running out of fuel again, jerks back and forth, loses power, rpms ALL over the place, and I have to keep revving him in neutral until I can turn around and make it back home (if Im lucky).

Im lost....

 

Get some diesel fuel treatment, or some people use transmission fluid. I guess you could also use that sea foam stuff.

Take your fuel filter back off, pour it out in a container, and then pour the treatment into the filter full strength. Start the engine and let it idle for a minute or so and shut it off. Let it sit overnight and then the next day give it a good run and see if it straightens out. It sounds like something is stuck inside the injection pump. With that many miles, I am assuming you have changed the injection pump out or had it rebuilt at least once correct?

 

I tend to agree with Dave sounds like the injection pump is going. I use marvel mystery oil every other fill up and it keeps everything flowing pretty good. There is a screen on the inlet of the injection pump that can get clogged, how about the water seperator, they get old and sometimes people bypass that assembly. Give it a shot and see what happens.

 

Seafoam... I have ran a can of seafoam through with a full tank recently, forgot to mention that, but you say to fill the fuel filter with all sea foam and start her up? ok i'll try that.

As far as the IP... I was worried that may be the problem, ( and as I got the truck from my dad in 2009 and has since passed, I am not sure if the IP has been replaced or not) and am really really hoping it is not, as that is a pretty penny to replace. How can I get to the screen to make sure that is clean?

 

Pour it in the filter so it's full strength, and then start and run the engine for a minute so it goes full strength into the injection pump, and then stop the engine. That will let the sea foam sit in the injection pump full strength and loosen anything up. Then start it up later on. I would let it sit overnight with the full strength stuff sitting in the pump.

 

Ok. gonna do that now then! If this works Im going to be so happy haha

 

Ok, tried the seafoam idea, didn't change anything, about to go take the IP off and mess with it. Is there a way I can take it apart give a good deep clean with some brake cleaner or something? I know you mentioned rebuilding it, I wasn't aware you could rebuild these, so I can only assume I can take it apart and maybe some ports or something are just gummed up? kinda like cleaning a carb?

 

You can't take it apart. It's not like a carb that you can rebuild. It's pretty complicated inside, and if you did get it apart and back together, you need a expensive machine to calibrate it. Even if you do take it off and take it to a fuel injection shop for them to rebuild, you are going to need the setup to time the engine correctly once you get it back on.

 

It is also kinda possible it truly is a supply problem. Need to be sure that all the fuel lines are sealing, and also that the transfer pump is doing fine. A quick safety check, check out your engine oil level to be sure it is where you expect it, and also is not runny, but acts like regular oil. Sometimes the diaphragm in the pump can tear a bit and leak into the engine oil.

 

If you do pull the injection pump, do not remove the 4 vertical bolts holding the aluminum housing in place, this will remove the timing gear as well, requiring you to re-time the geartrain, which is a pain to say the least.

 

OK! You know those times, when you do something, and then you find out you shouldn't have done it?? well, this is one of those times. I broke the small bolt off of the triangle cover on the injection pump, when i tuned up the amount of fuel the injection pump puts out, well, the only way i could drill out that broken bolt, was to take the injection pump off....

wellllll.... I took it off with the metal fuel lines, and the part where you add oil, is that the aluminum housing you were talking about that I shouldn't remove??

I came on here just now to say, I replaced some cracked fuel lines, and I am no longer getting air in my fuel, However, I am POURING out PLUMES of black smoke, even at an idle, so i tuned my IP back down to get less fuel, but still, massive amounts of black smoke, and it chokes out if I put it in gear.. so now that I may have removed something I shouldn't have, would it be a timing problem??

 

Probably the timing. There is a gear that drives the pump. He is saying you should leave the cover that goes around the gear on, and just pull the pump shaft out of the gear. If you pull the cover and then pull the gear and the pump off, then there is a very good chance when you put it back on it's lined up on the wrong tooth.

To get it all back right you have to turn the engine to a certain spot and then line up all the marks on the gears on the front of the engine. The problem is you can't hardly see the marks on the other gears without taking the front of the engine apart. If you get a light and a mirror, you might be able to see it.

Then once you get the marks lined up, you still have to time the engine with a special gizmo that reads the pulses on #1 injector line.

 

well thats just great... anyone have any info or posts on how I can do this WITHOUT any special tools? or an approx cost for someone else to do it?

 

I have successfully re-installed the timing cover and gear twice, without tearing down the front of the engine.
This article will help you get it back together, and at the very least static timed:
"Talk about Timing!!"