Ditto, Roy! When the manufacturers started running higher idle speeds/throttle openings in the mid-1980's to tweak emissions, they also started using a solenoid valve in the idle circuit to positively stop fuel flow. They were called- - - -wait for it- - - -"Anti-Dieseling solenoids"!
Run-on without fuel to keep the process going is impossible! That's why a Diesel engine STOPS when the fuel is shut off! We could cheat a little on hydrocarbon emissions tests by retarding the timing and leaning out the mixture, but neither of those procedures had anything to do with Dieseling on shutdown. They did make the exhaust manifolds glow cherry-red on the way to the emissions test station, though!
Jerry
