2005 Mercury 225 Saltwater Alarm Problem

K

Kodiboatie

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Jul 10, 2010
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I have had a warning horn issue on my starboard engine that started out as an intermittent warning with no indications of overheat, oil pressure probs, etc. The problem got worse when the horn came on while running in and caused the 2000 rpm limiter to kick in. As soon as the engine cooled almost completely, the alarm went away. Now it comes on once it has idled (or run) and gets to operating temp, and will only go off once the engine is nearly cooled. Again no signs of an overheat. I replaced the thermo sensor, thermal switches and thermostats, but it didn't resolve it. The local Yamaha mech (no Merc mechs within reach where I live) came down to the boat and plugged in his diagnostic lap top (which worked fine since this series was made by Yamaha). The program did not locate any faults and showed all systems working as advertised. All the while the alarm is blaring. He then switched the starboard engine harness through the port engine controls. The alarm sounded on the port side once the starboard engine reached operating temp. The alarms in both systems sounded weak and sickly, but I know for sure that the port horn is strong. This ruled out the control wiring and horn as a possible cause. Is it possible that the ECM is bad and sending a weak signal through the alarm system? Maybe some other component? I would be grateful for any other ideas or suggestions.
 
K

Kodiboatie

Recruit
Joined
Jul 10, 2010
Messages
5
Re: 2005 Mercury 225 Saltwater Alarm Problem

That's one of the first things I thought of, but I can't find anything in the wiring or at the connections or sensors. If I have a wire grounding out it is either buried in the wrapped wire bundle or in the ECM itself. Or I have some other issue cropping up outside normal sensor/alarm triggering parameters. I disconnected each sensor/switch to try to isolate the cause of the alarm, but it didn't work. Then I started changing components, but that didn't work. Then had the diagnostic on it with no faults registering, then swapped engine controls to isolate a control harness/ horn problem. The only thing I haven't replaced (in the temp sensing/ thermo system) is the ECM $$$$ and the actual wiring harness. I ran the engine yesterday for 20 minutes without the alarm going off (the longest period since this started), but I doubt it's fixed itself. I pulled the boat for hull cleaning and routine maint. and will continue digging. if I figure it out I'll post the solution.

Thanks!
 
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