Mercrusier 6.2 MPI Horizon engine won't shut off.

[grandfour]

I have a problem that others may have seen before and looking for some advice.

Last weekend doing some work on boat and had shut battery switch to ALL OFF. I was replacing a Trim gauge in instrument panel. When I switched battery back to ALL ON position I heard the engine go into what is the Pre Start mode, Alarm chirped once as it always does when I turn key on, Fuel pump pressurized and ready to start. Problem is, Key was not in ignition and switch was not on. Didn't think much about it and later I used the key to start engine and it started and ran normally for about 20 minutes. I then turned key switch to OFF position and the engine did not shut off.

Had no issues with ignition switch to this point. Had no way to shut off engine. I got a mechanic from marina and he tried pulling a power wire from ignition switch that should have removed power to computer module that keeps engine running. Still didn't shut off. He eventually pulled power for coil to get engine to shut down.

Turned battery switch to ALL OFF. I checked the ignition switch and it ohmed out OK. Mechanic said there was something keeping power to the computer module that kept engine going.

He was going to come by this week with a scanner to see what codes he could read if any. Has not been by yet.

Curious if anyone else has had a problem like this. It is a 2005 6.2 MPI Horizon engine. Been running without issue and has not had any recent work other than oil change.

Thanks in advance for your help.

Rick

 

[Bt Doctur]

one way is from a bad diode in the alt backfeeding the system

 

[Fun Times]

Just always be sure the engine is off before turning off the battery switch.

Did you try turning off your ignition safety lanyard kill switch to see if the engine will stop? If pulling the kill switch didn't help then the problem should be further downstream around the engine area.

Do you see a 12 volt power reading at the 12v gauge with the key on and off even with the kill switch pulled?? If so then possibly a problem up in the helm area.

One of your relays mounted on top of the engine may be stuck in the on position ....First with the key on engine off, try tapping on them all to see if the ignition system shuts off.....Then try swapping the relays around and see if the symptoms changes any...One relay will be a Main power relay and the other is for the fuel pump and signals the ECM is ready to start.

 

[alldodge]

replacing a Trim gauge in instrument panel.

Howdy

Worked fine before replacing gauge, now it won't shut off. I would suggest going back to the trim gauge and see if something was not wired correctly, or crossed

 

[Bondo]

I was replacing a Trim gauge in instrument panel.

Ayuh,...... Welcome Aboard,.... AD beat me to it,....

I'm bettin' yer Problem is related to what or where you were just workin' on wirin',....