Port Engine Continues To Run Even With Key Removed...

[mbjezior]

Has happened twice now...go to shut down when docked and port motor continues to run when in the off position - key can be removed yet still runs...only way to shut down is by port fuel valve to OFF.
Thought it was a bad ignition switch- replaced it- tested it- worked normally. Then when back at dock omce again it failed to shut down.
I’ve been reading a ton and maybe an alternator diode? Have an alternator on order..
Could be the wiring harness maybe?
Has anyone had this issue?

1994 Carver 370 Aft Cabin
Crusader 454XL w Holley Fuel Injectors

[bud37]

Interesting.....only seen that once, ......do you have the engine wiring diagram, is there a main start relay in it that feeds the ignition and fuel pump, may be stuck or sticking....have your alternator tested before you replace it, could be nothing wrong with it....thats all I can think of without seeing a schematic....

[km1125]

Any other accessories wired into that engine that are acting 'funky'? A bad ground that's common between two accessories can 'backfeed' voltage into the IGN circuit and fool the ECM into thinking the key is still on.

I did this inadvertently to a truck once. Wired an LED into the ignition so it would light when the key was OFF and go OFF when the key was ON. Worked great, except there was a trickle of current going through when the IGN was on, so if the vehicle was started, it would not shut off. A bad ground between two accessories can do the same thing.

[Midnightsun]

Boat ignitions in general are rather simplistic, 3 wires is all there is. One has constant 12v, one is ignition feed and the other is starter feed. Connect the 12v to ignition and you have power to run the engine, this is the one you need to trace back which should be purple in colour. Momentarily connect the 12v to the starter and you operate the starter motor. As mentioned, a led light interconnected to this power source does have a small amount of current which could trick the engine into thinking the ignition is off. Think back to anything electric you may have added in the recent past and disconnect to test.

Good luck in your findings and report back with the solution to the issue.

[Viper]

Could be anything mentioned above including an alternator diode. In my experience the alternator being the cause of this particular symptom is rare but it does happen.

[km1125]

I can't see where one of the normal "alternator diodes" could cause this. Perhaps they mean a diode in the regulator for the alternator (which could be in the alternator when the regulator is included).

[bud37]

One of those things that rarely crops up that makes you consider how a gas engine is actually turned off....anyhow he has a Holley retrofit I think from his signature, so it may have the relays, who knows.... alt. backfeed will do it as well....hopefully he posts the resolution.

[mbjezior]

Won’t be until Tuesday before I can check/test the alternator for diode failure...will do that first and report back. Have an alternator on order as backup, also will change out the ignition relay too...

[Viper]

One of the benefits of having two engines is that you can use that to your advantage as a diagnostic tool. When in doubt, swap a part from one engine to another and see if the fault follows the part.

[mbjezior]

Results...tested both the good alternator and the suspected “bad” alternator diodes and all checked out good- same on both.
I did replace the ignition relay on the port side- will run it wednesday for a period of time and will report back...