Need Help! Intermittent alarm question

District320

Hello all - I would appreciate any insight on an intermittent alarm issue I have been having (see example video below). Background/facts:

1. 2008 Rinker 320 w/5.0MPIs (B3s)
2. The port engine was rebuilt late last year (water intrusion as result of a bad manifold)
3. Immediately following the rebuild, this intermittent alarm began on the port (rebuilt) engine. As shown in the video, it is a brief beep coupled with brief loss of RPM, which immediately returns without any action taken. Sometimes it happens frequently and then goes away; other times I can run for hours and have zero issues/alarms. It doesn't seem to make any sense when or why it happens or the frequency of it appearing.
4. All other gauges and temps/fluids are normal
5. My mechanic said it is not putting off any codes on the computer. In fact, when he has had the code reader hooked up to the engine when this beep has occurred, he temporarily loses connection on the code reader at the same time it beeps.
6. Mechanic switched ECMs to see if the problem would follow to the other engine; it did not (so it does not appear to be an ECM issue)
7. Issue only happens at cruise; it has never happened at idle or off-plane speed/RPM

Here is an example I found on Youtube. This is not my boat but the same issue. Video here.

We are stumped as to how to continue trouble shooting this. Would appreciate any insight from folks who have seen this and/or have ideas on what could be the problem. Thanks in advance!

YYZRC

Sounds electrical. I would check the grounds first - especially at the engine that was removed. 

Ian

There’s a large harness plug on the top near the back - round multipin. Check that for any corrosion of pins but also check if the clamp is too tight. Seems that was my intermittent issue a while ago, tweaked up too tight and creating a dodgy connection at times.

LaRea

The symptoms sound like Bravoitis!  (Google it)

LaRea

Slight further explanation:  Bravoitis is a corrosion problem that restricts cooling water coming in from the outdrive.  It's caused by corrosion in the transom hose fitting.  In some cases, there's no error code and all sensors read normal, but a high reading from the exhaust temp sensor puts the engine in limp mode.  The only way to fix it is remove the drive and replace the fitting. 

The only symptom not consistent with Bravoitis is "temporarily loses connection on the code reader at the same time it beeps."

PickleRick

Not sure on your model but on my model the oil pressure system has two separate sensors. One for the alarm system and another for the gauge.   Iirc these are usually NC to ground.  The oil pressure opens them to break the connection to ground.   Just unplugging them and going on a test run could eliminate these as culprit. You're not usually looking for them, especially since the gauges read normal. Mine would work for about 5-10 minutes then set off the alarm when it went bad.

You could unplug each.  Not sure if these will kick a limp mode that will drop rpms aka limp mode. 

My temp switch is one large complicated multi wire switch that operates my glow plugs, alarm sensor and dash gauge.  Each wire can be tested individually with an ohm meters, infrared thermometer and a pot of water on top of a stove.   

Do you also have temp sensors on the manifolds that could be setting it off?   If you're slowly starting to lose water pressure I would think the manifolds would see temps spikes before the engine temp gauge were to start increasing.   This theory goes along with @LaRea, an issue that is just starting and could start getting worse.

YYZRC

@LaRea does bravoitis present itself at idle or trolling speeds? I thought it typically presented at higher RPMs?

LaRea

Right - only at high RPM.  

District320

Thanks, all, for the suggestions and insights. Much appreciated and helpful. I will update when we finally get this nailed down and figured out.