Well, you have a couple things to check. First I would try a new fuel filter. If it is getting clogged up, the pump could be sucking air from the front seal becuase it is building up a vacume in the fuel supply. Even after 4 months, if there is crap in your tank its very possible that the filter is getting clogged. I would also install a vacume gauge inline between the filter and the pump. With the new filter installed, if your getting a vacume of more than 1 or 2 inches there is a restriction somewhere else like at the fuel tank pickup. I'm not sure if your model has a screen in the tank over the pickup but some do. If the filter makes no difference and you dont have excessive vacume I would do this next: Get a piece of fuel hose and a jar of diesel fuel. You need to hold the jar above the injection pump and try to run it that way. If it runs well, you probably have a leaking front shaft seal that is sucking in air rather than fuel. By doing this, the pump is being gravity fed and not relying on the vien pump to suck fuel into the pump. These can leak air into the system without necesarily leaking fuel out. If that is the case and it runs smoothly, than you need to install a new front shaft seal, it is found behind the drive pulley/sprocket on the pump. If this doesn't make a difference, I would start checking injectors. I have had one with a piece of crap hang a nozzle open and compression gas from the engine was being forced back into the pump and filling it with air, making it run like crap and very hard to start once you shut it off. You would get a big blast of foam from the feedline when you shut it off. I know the delivery valves are a one way valve, but they are not a totally positive seal and air can go backwards into the pump, I've had it happen to me. That's about all I can think of at the moment. If you don't have a pop tester or access to one, you can remove one line at a time from the injectors and hold it to the side, diesel will be squirting out, but if the injector is fualty as I'm describing, short little blasts of air will be shooting out of the injector inlet.
Hope this is helpfull.
Jason
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