Tractor won't start, fuel relayed but I'm stuck

[STx]

I've got a New Holland TC40DA. The other day I couldn't get it started, I replaced the fuel filter, it started up, ran rough for a bit and was then fine. Yesterday, it didn't want to start again, I cranked it a bit and it eventually started, ran great. Today, I couldn't get it started again, I removed the fuel filter and cleaned the bowl, it started but stalled. I took off the fuel line at the filter from the tank and blew air back and it's gravity flowing well. I then pulled the return line and blew air through it, cranked the motor and fuel came out of the connection at the filter. I pulled the line going into the fuel pump and it's gravity flowing well so I pulled the line from the fuel pump to the injector pump and get very little flow.

Here's where I get stuck, with the line removed at the injector pump, it cranks right up. I get some fuel from the fuel pump but, it's less flow than the gravity lines and looks aerated. If I hook the line back up, tractor runs great until I shut it down. Once I turn it off, I can't get it started again without removing this line. It's like it's getting an air lock or vacuum that's preventing the fuel from flowing.

My guess is that it might be the fuel pump? It's a mechanical pump and I've only got 1300ish hours on the machine do that seems odd to me but, I can't think what else might be causing it.

Do you guys have any ideas?

 

[STx]

In case anyone ever comes across this searching for a solution, it ended up being a defective operator safety module that was intermittently powering the fuel shutoff solenoid on the injector pump. I've already bypassed most of the safeties because of the problem that is common in this tractor's starting circuit so I just put a shunt I to the wiring harness to solve the problem. Nobody drives the tractor but me and there aren't any kids here to worry about.