2003 Mercruiser 5.0 MPI will not shut off. Bad ECM?

[Gambme]

I have a 2003 Merc. 5.0 MPI. The engine will
not shut off when the key is switched off. The
problem is electrical... it is not dieseling..

Even if I turn the ignition on but not start the
engine, when I turn the key off the ignition is
still on. Turning off the battery will turn the
ignition off.

if the engine or running it will keep running even
with the key off. It will keep running even if I
turn off the battery ( I know, that is a bad thing to
do).

the mechanic thinks it is the ECM. He said the ECM is
not grounding the stop circuit.

before I spend $2500 on a new ECM can anyone think
of another culprit? What about the main power relay ?

Appreciate any thoughts...

 

[Rick Stephens]

First thing to check is power from the ignition switch is being turned off when the key is turned to off. No power to ECM, no spark.

 

[Bt Doctur]

a shorted diode in the alt will allow it to backfeed the ign system

 

[tpenfield]

:welcome: to iBoats . . .

Yes, check the easy stuff first . . . ECM would be last on the list.

 

[muc]

You didn’t post a serial number for this engine, so I can’t comment on what your problem is.
The ECM maybe bad, turning off the battery switch while the engine is running makes it very likely.
If you install a new ECM and there is a problem with the wiring or MPR you have a good chance of ruining the new ECM.

There is no “stop circuit” in the ECM. So I’m not sure how it could be grounded.
Might want to get a 2nd opinion.

 

[Mark-p]

Check the Orange wire from the alternator to the starter.

it may be shorting out on the alternator bracket or post.

Or ignition switch bad?

 

[Searay205]

Even the Merc service manual indicates the PCM are very reliable and only replaced as last resort. find new mechanic