The solenoid is for shutting off the fuel, not opening up the individual injector pumps' fuel meters. The loud clack when you shut off your key is the solenoid releasing its plunger to slam forward and block the governor from increasing the fuel supply. When you turn on the key, it pulls away from the rack gear that the governor pushes aft to increase the fuel through the three injector pump pistons.
I had an issue that could have been this same one with my 7274. In my opinion, that shutoff solenoid has too powerful of a return spring, and it slams that rack gear forward too hard when you shut off the key, and it can break a tooth off one of the three pinions, and that broken tooth can get stick in between the rack gear and the broken pinion. That rack gear rotates the metering rods in the three pumps via the three pinions.
I was able to take my pump apart and find the broken pinion. Being careful to not mix the parts from the three pumps, I replaced the broken pinion, which I got through a fuel injection specialty shop in Portland, OR. The pinion cost $7 and saved me the $1300 that I had found a pump selling for online.
With the broken tooth gotten out of the way, you could have only two of the pumps working at full capacity. The pinion with the missing tooth would only rotate the metering rod so far. The tractor would run again, but one cylinder could possibly be running lean. Mine would not run at all when the broken tooth was jamming the rack gear.
Though the guy at the fuel injection shop had never heard of this problem, I still live in fear of it happening again, every time I shut off the key and hear that loud clack!
All I did wrong was to turn off my key. It took me weeks with my tractor dead in my neighbor's front yard, cranking the engine for hours on end, and all my diesel expert friends standing there and scratching their heads along with me. It was not easy to work on with the loader in the way.
I know I'm late with this, but it might help someone else.