Mercruiser Bogus Alarm

Senior B

Petty Officer 1st Class
Joined
May 19, 2006
Messages
253
Im posting this for a friend of mine. His craft is a 1999 Chaparral Sunesta with a Mercruiser EFI 5.0 and Alpha Drive. The issue is a constant warning alarm that sounds as soon as you turn on the key. The boat starts and runs fine and gets full rpm on the water. I come to understand that there are 3 things that trigger this alarm: 1. Low oil pressure, but that should kill power to the fuel pump and the boat runs at 50 psi now. 2. Over temp that should put it limp home mode and limit rpms to 2500. It has a new impeller in the out drive and runs @175 degress which is pretty text book for the EFI and it's not limited on the rpm. 3. Low oil level in the out drive resevour. It's full and the float switch moves. I am leaning toward a bad switch on # 3 since the alarm sounds as soon as you turn the key on and never stops. Is there something that we may be missing?? Thanks..
 

fossill

Chief Petty Officer
Joined
Jun 20, 2009
Messages
427
Re: Mercruiser Bogus Alarm

The alarm always sounds with the engine off and key on. It silences once the engine starts up. I's triggered by low oil pressure, high water temp, low oil level in the stern drive monitor. Thats the way mine works anyway. I'd unplug one sensor at a time till it quits to find the faulty one. Also check wire connections.
 

Senior B

Petty Officer 1st Class
Joined
May 19, 2006
Messages
253
Re: Mercruiser Bogus Alarm

I'll clarify that it sounds all the time from the time you turn the key and it sounds even when running. Am I correct on what will trigger those alarms and what they do? I.e limit rpm, kill power to the fuel pump ect.
 

Bondo

Moderator
Staff member
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Apr 17, 2002
Messages
71,137
Re: Mercruiser Bogus Alarm

I'd unplug one sensor at a time till it quits to find the faulty one.

Ayuh,... There's the Answer to how to Diagnose the Problem....
 

TilliamWe

Banned
Joined
Dec 21, 2004
Messages
6,579
Re: Mercruiser Bogus Alarm

I'd unplug one sensor at a time till it quits to find the faulty one. Also check wire connections.

Yep, big old + 2 on this suggestion. The drive oil wires are the easiest to reach, followed by the temp sensor on the thermostat housing. I am not really sure where the oil sensor is. Maybe in the back, by the distributor?
 
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