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Rawze

NOTE: The engine will run fine ... and shut down just fine with the guts removed from the fuel shut off solenoid.

The solenoid itself is a secondary safety feature only. - Otherwise, if someone does remove its guts... and then the engine stumbles and does not shut off right away with key-off then this is a clear sign of a fuel (metering) solenoid in the IFSM is also getting leaky and/or a leaky injector (or 2) is causing it.

That being said.. the only way to likely find out why the solenoid is randomly being commanded to shut for like you describe would be to monitor the engine data via Calt$erm software.

On a guess however ...

== My first guess would be a flaky ecm. Those ecm are notorious for getting flaky and cutting out randomly as they get age on them, or suffer excessive vibrations. - This is very common as they get old, especially if no one has bothered to replace the crank shaft damper at 500k mile mark.. to prevent higher frequency vibrations.. which is well known for making ECM flaky. These days, you could put 10 used ecm's on and find that all 10 are flaky .. and then swear its something else. - Banging on the ecm itself hard (almost enough to dent its casing) will reveal it, making it cut out.

NOTE: It is also VERY EASY to damage the shutoff solenoid circuit output if some idiot tried to jump the voltage to it from the batteries .. and they do not disconnect the wire for it that goes to the ecm. - Voltage will back-feed thru the wire and short out / damage the circuit that activates it inside the ECM and then it gets flaky as h$ell or it fries all together internally in the ecm. This is NOT a good thing... and its very easy for some idiot to do this.

== My next guess would be .. if it is not the ecm itself... would be the key-switch in the dash signal getting flaky into the ecm. ECM is getting an Intermittent signal to tell it that the keys-witch in the dash of the vehicle is no longer on. - This is common too.

== My third guess .. if there is any normal logical reason for ecm to only temporarily shut it off... would be an over-pressure (spiked pressure) event in the IFSM .. and the ecm shuts off the solenoid for a moment to protect the engine/IFSM ... but that should throw an alarm ... one never knows, but maybe not if it happens, then recovers fast enough.

I.E.> If there is a leaky injector because the overhead rockers are out of adjustment badly, and / or simply a leaky injector getting bad enough ... a bad injector can back-feed combustion pressure backwards into the IFSM and spike the fuel pressure. Doing a proper injector leak test(S) on the engine will reveal this ...
info: https://rawze.com/forums/showthread.php?...8#pid67948

... just some thoughts... the beer is talkin'.