When full throttle: Audible beep and powers down

[Eaglerider94]

Hi everyone,

Newbie here. After full throttling a Bravo Mercruiser HO (04" Lavey) , an audible alarm sounds and the engine goes into I believe "limp mode". Water temp hasn't exceeded 140 degrees.
Crystallization was scrapped out of the original hose last year plus the boat hasn't been in the water all year.
Was suggested replacing the water pressure sensor which I did yesterday but of course that wasn't issue. Now I'm thinking if it was faulty, it wouldn't have sounded?

Anyone care to point me in a direction I can look into?

It was a constant beep. Would that suggest a specific issue or are all the alarms a constant beep?

 

[TimTJR]

The audible system for Mercruiser Alpha will sound under 3 conditions.
1) Insufficient oil pressure
2) Excessive engine temperature
3) Insufficient drive lube

I wouldn't imagine this would be different for Bravo.

Check out the link below on page 27.

http://www.spidybot.com/merc4_3alpha.pdf

 

[alldodge]

What motor and what's the serial number?

 

[achris]

The audible system for Mercruiser Alpha will sound under 3 conditions.
1) Insufficient oil pressure
2) Excessive engine temperature
3) Insufficient drive lube

I wouldn't imagine this would be different for Bravo.

Check out the link below on page 27.

http://www.spidybot.com/merc4_3alpha.pdf

If it's MPI, there are a lot more alarm conditions than that!

 

[Eaglerider94]

What motor and what's the serial number?

I asked the mechanic and they don't have it. It's a MAG496HO (8.1L)

 

[achris]

I asked the mechanic and they don't have it. It's a MAG496HO (8.1L)

Nope, it's on the engine itself. Usually (but not always) in 3 places.
1. On an aluminium tag just above the starter.
2. On the flame arrestor cover.
3. On the engine specs decal on the rocker cover.

The fact the the engine goes into 'Guardian' mode, and it's sounding the alarm suggests the ECU is sensing a fault. You need to get a scantool, or the Rinda diagnostic software hooked up and check to see which codes have been set. Some codes will be there regardless, possibly things like fuel sensors, steering sensors, but those are normal. You're looking for an engine fault code. Something like an oil pressure, or seawater pressure, or a crank (or cam) position sensor... Could even be an IAC, pretty common on the 8.1s to cook the IACs... Do a lot of idling?

Chris......

 

[alldodge]

Crystallization was scrapped out of the original hose last year
MAG496HO 2004

It has Bravoits and the hose was scrapped out, so it could also have other restriction inside the hose

The 8.1 has other alarms

Overspeed
Port/Starboard Manifold overheat (being an 04 these might be present)

If this starts around 2000 rpm then the in gear switch is possible
If you install a mechanical gauge on the block the pressure can be read to determine

 

[Pappytoon]

Had a continuous beep at full throttle, sometimes on a 2019 90 hp. No sign of over revving engine but would get a little ventilation of cavitation feel periodically ( normal pontoon). Popped in a new hub kit, problem solved. Old hub rubber looked good, but was apparently allowing some slip. Hope this helps somebody else.