Mercruiser 2 beeps/minute alarm diagnosis Sherlock

[the man]

Okay here is one for Sherlock Holmes:

I have a 2004 Mercruiser 5.0 MPI SN OW003759 with Bravo 3 SN OW108118.

The two beeps per minute alarm is going off. Below are the facts of the case as I can best tell-

1) I can run the engine at 1800rpm for two hours (did it) with no alarm.
2) It only starts to sound when the boat is on a plane (RPM 3200 +)
3) When I back off the throttle to less than planing speed, even all the way to idle, the alarm will keep beeping
4) I can stop and immediately re-start the engine and the alarm will not sound until higher revs again (planing power)
5) If I run WOT for more than 5 seconds or so, alarm will become a continuous warning sound (not an intermitent beep). When I reduce throttle at all, it goes back to two beeps/minute.
6) All fluids are correct, engine is not overheating, oil pressure is 40-43, hard to tell from stock gauge but looks like 14.4 volts at speed.
7) At idle, in gear, engine will sometimes (with no regularity) speed up 100 rpms or so for a second or two.
8) It has also recently stalled while idle-ing at the dock a couple of times; starts right back up.

any ideas?

 

[david2027]

Re: Mercruiser 2 beeps/minute alarm diagnosis Sherlock

I had alarm issues similar to yours awhile back. It would go off under a variety of conditions and all the fluids, temp, and oil pressure were ok. Would stall at idle too which was a real pain at the dock. Dealer diagnosed a intermittent fault with the shift interrupt switch, replaced it and the problem went away.

 

[burp]

Re: Mercruiser 2 beeps/minute alarm diagnosis Sherlock

There are a bunch of conditions which will generate the 2 beep per minute alarm. The constant alarm, I would think would be caused by a different problem. Once the alarm condition occurs, stopping and restarting the engine is just resetting the alarm until the condition that is creating the alarm reoccurs.

Stalling and rough idle/uneven idle RPM's are symptoms which can be caused by a defective IAC valve. IAC problems will generate the 2 beeps per minute alarm.

For the constant alarm, I'd top off the outdrive lube reservoir to see if that is the source of the constant alarm. Another thought for the constant alarm, since it occurs at WOT is engine overspeed. (ie: under propped) What is your engine RPM's compared to the maximum RPM's for which the engine is rated?

Having the ECM error log read out by a shop or someone with the Merc DDT/doagnostic software will tell you more on the source of the alarm conditions.

 

[Don S]

Re: Mercruiser 2 beeps/minute alarm diagnosis Sherlock

Here is the chart that shows all the alarms and what can cause them.
http://www.4shared.com/document/wQ5qgap8/555_Audio_Alarm_chart.html

 

[the man]

Re: Mercruiser 2 beeps/minute alarm diagnosis Sherlock

.

For the constant alarm, I'd top off the outdrive lube reservoir to see if that is the source of the constant alarm. Another thought for the constant alarm, since it occurs at WOT is engine overspeed. (ie: under propped) What is your engine RPM's compared to the maximum RPM's for which the engine is rated?

I have heard the alarm for low fluid in the drive resevoir- it is a constant beeping; this is an uninterupted sound. Also the WOT RPM is about 4500, maybe 4600. This boat has been used for years with the same prop setup, and WOT has never caused an alarm before.