Engine won't stop running when ignition switch is turned off

2000 Sea Ray 215 Express Cruiser with a 5.0L EFI Mercruiser 240 HP Serial #0L657855
Alpha MCM Stern Drive

Engine won't stop running when ignition switch is turned off:
- All of the gauges all turn off and the radio / lights when the ignition switch is turned off
- Turned off battery switch and engine still runs
- Kill switch doesn't stop the engine either - but it does prevent the boat from starting when Kill switch is off.

Dealer looked at the issue last year and couldn't get it to repeat. I replaced the ignition switch and it seem to work but the problem came back.

It happened again this year when out on the river a few weeks ago. The dealer said it was the spark plug wire that was running directly over the distributor cap and arching, which caused the plugs to continue to fire. The new spark plugs didn't help, still doing it. The dealer is going to troubleshoot it again but now they are talking about replacing the ECM, which is estimated to be around $1500.

Also, I read that the ECM shut down the fuel pump to stop ?dieseling?, so I'm not sure how the spark plug arching could keep the engine running if that is indeed the issue (which we found out it is not!).

Now I'm reading that others that need a new ECM are also going to have to buy a newer version of an ECM along with an adaptor kit for older boats adding up to $2600+

I'm hoping others that might have experienced something similar (or heard of others that have) might have some other ideas. I'd like to try other things before spending up to $3000 for parts and labor!

Any ideas / thoughts / suggestions

Re: Engine won't stop running when ignition switch is turned off

My guess is the diode in the alternator is NG and the alternator is backfeeding the ignition circuit even though the switch is off.

A diode (not a resistor), could be added externally very inexpensive, connect it so that the switched ignition power to the alternator passes thru it to the alternator. A diode only allows the flow of current in one direction. The diode will prevent current from going back to the ignition switch and this will prevent a "run on" condition when the ignition switch is turned off. Use a Radio Shack #1N4001 diode or an equivalent value

If that works you could keep it like that or rebuild/replace your alternator.

Re: Engine won't stop running when ignition switch is turned off

Eric 3.7LX Alpha 1 said:

My guess is the diode in the alternator is NG and the alternator is backfeeding the ignition circuit even though the switch is off.

Click to expand...

Ayuh,.... Alternator related was My 1st thought as well...

Re: Engine won't stop running when ignition switch is turned off

^+2

plus you should find a different dealer/mechanic

Re: Engine won't stop running when ignition switch is turned off

Here is my saga with with an engine that would not shut off (with pics) - turns out to be a post on the starter that was rotated when tightened and was touching the wire next to it , good luck

http://forums.iboats.com/showthread.php?t=404398

Re: Engine won't stop running when ignition switch is turned off

Thanks for all of the comments / ideas.

After a further discussion with the mechanic ran the engine for 15 minutes to allow it to heat up. He was able to trace it back to a bad relay. It worked fine when it first started but then wouldn't shut off the engine when it heats up. I ran it this weekend and it seems to have fixed the issue.

Thanks again!