Strange Alarm

[JohnnyS]

87' Merc BlackMax 150<br /><br />Sorry to post another engine alarm question, but I searched for this and could not find a similar post.<br /><br />My issue: Sporadic engine alarm. The motor is running nicley (all RPM ranges)- same amount of smoke as always, nice strong 'pisser', no power or control problems.<br /><br />Every now and then the alarm goes off (screaming). When this happens, I stop the engine, then immediatley re-start it, and the alarm is gone. I noticed that merely puting it in neutral does not stop the alarm, I have to turn it off. But immediately re-starting it does not cause the alarm to come back.<br />It sometimes comes back later on- sometimes it doesn't.<br /><br />What the bleep is going on - Help !<br /><br />Thanks<br />John

 

[waterkats]

Re: Strange Alarm

I logged into this site for what sounds like the same issue! We have a 1996 Mercury 175 XL outboard. Serial number 0G336567. We run this on a 21' 1996 Bayliner Trophy WA.<br />The motor runs great at all rpms but occassionally has been sounding the overheat alarm. We had the water pump replaced a little over a year ago and have less than 4 tanks of fuel through it (this was suggested maint. - not repair) When the alarm sounds, continuous beep, we throttle back to neutral and shut it down. (There is a steady stream coming out the water pump indicator hole) We can start it back up right away and no problem - no alarm! <br />In the past month we have:<br />- replaced the spark plugs<br />- cleaned the battery terminal connections<br />- cleaned the water (bypass) regulator<br />- checked the tattle tale hole - no leaks<br />- replaced fuel filter<br />- replaced the tempurature sensor and switch<br />- replaced thermostats<br /><br />We had her out this weekend and sure enough...the alarm sounded, with more experimenting and checking, we found the alarm was sounding only when we cruised her right at 3000 rpm...we are at out wits end...the motor does not seem to be running hot yet the alarm sounds. You can run wot and no alarm! The motor starts, idles and runs great otherwise. Any help is appreciated!<br />(This motor has been in salt only twice and was flushed thoroughly each time. Anodes are fine)<br />Thanks!<br />direct e-mail is Diane.Davis@kosa.com

 

[JohnnyS]

Re: Strange Alarm

Shameless BUMP.... <br /><br />Still need help <br /><br />Thanks <br />John

 

[NICK JONES]

Re: Strange Alarm

Had a similar problem and it turned out to be a faulty alarm module. This is the black box about 5" x 4 " x 1" thick on the port side of the engine with 5 wires. It also forms the oil alarm monitoring and output circuit. On mine you could actually stop and start the alarm by giving the alarm module a sharp tap... Not good practice but proved the point !

 

[NICK JONES]

Re: Strange Alarm

Just another thought, you didn't say if the alarm was continuous (overheat) or bleep.... bleep.... bleep (oil). If it's oil you need to investigate carefully. I've had the outer switchbox fail and sometimes drop out the supply to number 4 coil. This signal is compared to the oil pump rotation sensor (by that alarm module) if the two don't match you get an alarm which comes and goes with the spark on No4. You might not notice that one cyl is not firing on the V6.

 

[JohnnyS]

Re: Strange Alarm

Thanks for the reply.<br /><br />Its definetly a continous beep (scream more like it). If thats more indicative of an overheat situation, then I'll look into the cooling system. Already replaced the Impeller this spring - and the 'pisser' is flowing well. Maybe its the thermostat or temp sensor. I'll look into that next. <br /><br />I have not noticed it missing, so I think all cylinders are firing. The motor runs fine at all times without hesitation through out the power range.