I'm not 100% familiar with this set up. Look on the injection pump for a little solenoid with one wire going to it. That will be your fuel shut off solenoid. Check for power there when key shut off. Likely it's sticking. You may be able to pull it off pump and clean up plunger. Easiest is to run a detergent additive like Deere's Keep Clean Fuel Protect through it. I've had success on my uncles Massey 8650 with a 5.9 cummins.