D4D 68A series

The rack is sticking because you have one or more injector pumps partially sized through water or dirt contamination, I'm sorry to say that it is trip to the fuel pump shop.

It may be possible to free the rack up by removing the governor cover on the end of the pump housing until you can get to the rod that connects to the rack. Then there should be a small cover on the opposite end of the injection pump housing which can be removed to access the opposite end of the rack so that you can work it back and forth. If it doesn't take a lot of force to move it back and forth, simply moving it a little may free up the plungers. Probably need to turn engine over (slowly or decompress!) as you're moving the rack back and forth.

As you know the throttle control linkage doesn't move the rack directly. The rack position is a result of the balance between the force exerted by the governor flyweights and the tension of the governor spring which we change by moving the throttle lever. If the spring does not have enough tension to move the rack to a "fuel on" position, the engine won't run as you describe. On the other hand, if the rack is stuck at a fuel on position and the governor weights cannot exert enough force on it to move it to reduce fuel delivery, then the engine overspeeds.

It is possible you will damage the fuel pump plungers calibration if you get rough with a frozen plunger, so undertake this at your own risk and ensure that you have a way to effectively smother or decompress the engine to stop it if it runs away when you start it up after getting the rack moving smoothly.

I was lucky enough to get the rack free on a DW20 (D337F engine) we were working on a few years ago. That engine has some external linkage that was accessible so we could pry the rack back and forth and it was really stiff for the first time back and forth. I was at the point of saying "nothing risked, nothing gained", but it worked out fine.

Good luck!

I would also take another look at that serial number, it could well be 88A, the 68A was the Glasgow built D8H between 1958 and 1973.

thanks for the help, i think we are gonna take the injector pump and control in to a shop and have it repaired. i think the control is locked up and not letting enough fuel in the engine to get her to fire. i worked on it again today and we were able to get some more air out of the lines and she sounded like she was gonna fire a few times but never fully did. i also talked to a couple guys that used to work on these old tractors and they said that the pump and control should be removed and taken in to a shop. does anyone have any shop manuals on this tractor? if not if i can get the step by step procedure on how to take the injector pump and governor off that would also work. thanks