Engine Alarm - 2000 MerCruiser 5.0 w/Bravo 3 - tried everything to fix

[MarbleheadJim]

So here's an interesting one. I have a 2000 SeaRay 21.5 ft with a MerCruiser 5.0 and Bravo 3 outdrive. I'm told it's a Thunderbird 5. I am getting a "beeping" alarm when I get my RPM's above approximately 3200 RPM. I also get the alarm when I "throttle up" quickly from idle to full throttle after about 5-10 seconds. When I back off from either condition, the alarm goes away. Boat runs real smooth, like nothing is wrong. It also does not go into "safety" mode and cut the throttle back - I can go as fast as I want. If I cruise around at 2800-3000 RPM no alarms. Runs fine. You'd swear nothing is wrong. Here is what has been done so far:

* Temp sensor changed (old and new show 170F on the gauge; no temp problem; impeller changed last year)
* Oil pressure sensor changed (old and new show 40 lbs on the gauge; no oil pressure problem; oil level good)
* Disconnected outdrive reservoir (no change; reservoir is full)
* Complete tune-up (plugs, cap, rotor, ignition module under rotor; spark wires are almost new)
* Fuel/water filter
* Carburetor was rebuilt 4 years ago (2-barrel throttle body injector, new needle valves (genuine - I was lucky to find!)

Once we did the complete tune-up, I noticed it wasn't alarming as easily when I throttled up from idle, but still got the high RPM alarm when I went above 3200-ish RPM. If it wasn't alarming, the boat runs like a champ. 507 hours on the engine, regular oil changes every season and full outdrive fluid changeout every season (average 50 hrs/season).

Any ideas???

 

[JustJason]

Have it scanned

 

[alldodge]

getting a "beeping" alarm when I get my RPM's above approximately 3200 RPM

Could use a serial number to verify but

Disconnect the in gear switch

 

[metsfan3197843]

If you have a sea water pressure sensor try unplugging the connector and seeing if it goes away. Sounds exactly like what mine was doing when I had a faulty PSI sensor.

 

[jesse_boston]

The sensor for the temp and the sensor for the oil gauge are entirely different sensors than the temp switch and oil pressure switch for the alarm circuit.

Similar to how the tilt on the outdrive has a sensor on the right for the gauge and a switch on the left for the limit... two separate systems.

Did you replace the senders or the switches for the temp and pressure?

Oil Pressure Switch for alarm system:


Oil Pressure Sender for gauge:


Here's the parts lookup for the 2000 5.0. Note that it lists the gauge sensor as #3 and the switch separately as #7.

 

[jesse_boston]

On mine it was the oil pressure switch.

 

[Scott Danforth]

welcome aboard. see post #3

 

[Fun Times]

In the year 2000/01 era, Merc wasn't using the gear switch just yet with the MEFI 3's and under...The gear switch started with the 555 ECM in late 2002 for the 03 model year for all smaller stern drive type MPI engine models except for the 496/8.1's starting in 2001.

That mentioned Merc should of still been using the fuel pressure sensor mounted to the throttle body for the older EFI's and/or to the fuel rail on the late model (98+) older MPI's depending on fuel delivery design.... Without a engine serial number to help confirm certain things about your engine model, the sensor may be item number 16 in the first link below and it would sound the horn at certain higher RPM's and ought to show up while performing an engine diagnostic scan of the electronic fuel injection system should it be having/giving you an actual issue as there are others that could sound the horn too....Plus jesse_boston is correct with any fuel injected engine, just because the analog gauges show all seems to be working well, the digital sensors that the ECM is reading could be showing a different reading that isn't reading correctly for some reason or other such as the 2 wire temperature sensor on the thermostat housing sounding the horn...Or one of the Mercruiser's discrete switch's like the oil switch shown above is activating at that RPM for some odd reason.

https://www.mercruiserparts.com/bam/subassembly/31846/4856/130

https://www.mercruiserparts.com/bam/subassembly/31846/4856/250

https://www.mercruiserparts.com/5-0l-efi-gm-305-v-8-1999-2001-0l331631

 

[dubs283]

you can keep throwing parts at it, cross your fingers and maybe get lucky

or, follow the suggestion of using a scan tool and verify what dtc is active when the issue arises

 

[MarbleheadJim]

Thanks to everyone that replied. I did have the computer scanned by a qualified technician. They were out on the boat for 30 minutes getting it into alarm mode but no code was appearing. Is this normal for a MEFI3 computer?

 

[alldodge]

Assuming a scanner connected to the motor, it did get code 12

After 1999 MEFI 3 has a soft and hard alarm.
Hard alarm engages above 3000 rpm. Soft alarm 1 beep for one second and off for 3 seconds.

Drive lube bottle low or switch in bottle is hung/shorting out internally, will be no code

Alarms with code
If fuel press drops for 5 seconds - this may go away if voltage comes back up
If voltage drops to 9V - this may also go away when voltage goes back up