Random alarm 5.7L carb'd Bravo 2

[skunkedskippy]

Random alarm - sometimes short chirps, sometimes solid for a few seconds. Only when in gear and at operating temp. The only patterns I noticed are that it often occurs just after I increase throttle. Also seems to occur more around 13-20 kts, and rarely above 23 kts (did not note the RPMs at these speeds).

If I unplug the coolant alarm sensor, the random alarm goes away. I replaced the sensor but alarm still sounds. Unplugged the new sensor and the alarm goes away.

Also bled the system (per service manual) which did not help. I feel like either I'm not bleeding properly, or there is a blockage in the housing where the sensor is mounted.

Here's what I know about my motor:
Mercruiser 5.7L serial# 0M009325
Closed cooling system with heat exchanger
Mercarb 2 barrel
Thunderbolt V ignition
Bravo 2 outdrive

Any help is appreciated.

 

[Scott06]

What does the engine temp look like ? Measure the water crossover with a IR thermometer. You may be running hot intermittently

 

[alldodge]

It may be a chafed wire. Power goes to the alarm and the Tan/Blue is grounded to sound the alarm. It can be the lube bottle, Temp sender and oil pressure switch.

Check the oil pressure switch, it can be Tee'd with the oil pressure sensor which goes to the gauge. 87-864252A01

 

[skunkedskippy]

What does the engine temp look like ? Measure the water crossover with a IR thermometer. You may be running hot intermittently

I did this the other day and it was reading 160, if I recall, on the housing that the sensor mounts into. I'll do it again this weekend on the water.

What is the 'water crossover'?

 

[skunkedskippy]

It may be a chafed wire. Power goes to the alarm and the Tan/Blue is grounded to sound the alarm. It can be the lube bottle, Temp sender and oil pressure switch.

Check the oil pressure switch, it can be Tee'd with the oil pressure sensor which goes to the gauge. 87-864252A01

Are the 3 sensor wires connected together before they go to the alarm? I followed the wires from the lube bottle, which get bundled with the coolant sensor, and then with the Mercathode wires, and then to a bunch of other wires. Can't tell if the wires are spliced, or just taped together. Hope this makes sense.

I'll ask another way. If 1 of the 3 sensors is bad, will the alarm stop even if I unplug one of the good sensors?

I can't find the oil pressure switch. From what I've read, it can be in multiple locations. Based on the info I listed above, can you tell where it would be?

 

[Fun Times]

Random alarm - sometimes short chirps, sometimes solid for a few seconds.
If I unplug the coolant alarm sensor, the random alarm goes away.
Mercruiser 5.7L serial# 0M009325

What year is the boat? 2006ish?

Try disconnecting the wire harnesses at the TB 5 Mercruiser ignition control module for a minute or 2 to see if it helps stop the warning horn form reactivating.

2014 Mercruiser 4.3 TKS - intermittent false overheat alarm

Hello all, This is my first post to the forum, I'll try to be as thorough as possible. First, the info: 2014 Larson LX195S - first owner 4.3 TKS (190) Alpha 1 High Five 19P 75 hours Used freshwater only - premium (94 octane) fuel Problem: intermittent sounding of overheat alarm Diagnosis...

forums.iboats.com

 

[alldodge]

I'll ask another way. If 1 of the 3 sensors is bad, will the alarm stop even if I unplug one of the good sensors?

No, and your issue is intermittent so it is hard to find

I can't find the oil pressure switch. From what I've read, it can be in multiple locations. Based on the info I listed above, can you tell where it would be?

The switch can be below and behind the distributor

 

[skunkedskippy]

What year is the boat? 2006ish?

Try disconnecting the wire harnesses at the TB 5 Mercruiser ignition control module for a minute or 2 to see if it helps stop the warning horn form reactivating.

2014 Mercruiser 4.3 TKS - intermittent false overheat alarm

Hello all, This is my first post to the forum, I'll try to be as thorough as possible. First, the info: 2014 Larson LX195S - first owner 4.3 TKS (190) Alpha 1 High Five 19P 75 hours Used freshwater only - premium (94 octane) fuel Problem: intermittent sounding of overheat alarm Diagnosis...

forums.iboats.com

Thank you for the link. I think you're right about the ICM. Unfortunately I can't seem to find anything resembling that pic on my motor. I believe it's a late 1990's model.

Here are pics of the Mercathode module, and the 'main harness'. Where would the ICM be, relative to these?

 

[skunkedskippy]

No, and your issue is intermittent so it is hard to find



The switch can be below and behind the distributor

Is it one of these? 1st pic, starboard. 2nd pic, port side.

But I read that unplugging this will cut off the fuel pump. So how would I test it?

 

[alldodge]

The TBV and knock module might be mounted to the exhaust elbow

This is the knock sensor
https://forums.iboats.com/attachments/img_7237-1-jpg.337926/

Your switch is this one on the right, and does look kind of rusty

 

[Scott06]

The TB module is seen directly behind your mercathode in the pic you posted. It is attched to the exhaust elbow. The knock sensor is piggybacked to it. The ignition module is the bigger rectangular module, the smaller one is the knock sensor

 

[skunkedskippy]

Thanks guys. I'll wiggle around with these on my driveway and see if I can get the alarm to sound. Any harm in unplugging any of these while running?

 

[alldodge]

No harm in unplugging
Its not a computer driver motor

 

[skunkedskippy]

On ear muffs, I wiggled wires but could not get the alarm to sound. I unplugged the ICM connectors one at a time - engine stalled when the 2 smaller connectors were unplugged.

Then I noticed the gear lube monitor was just below the "add" line so I topped it off.

On the water I heared the alarm chirpped only twice throughout the entire day. Not sure if it was the gear lube level, unplugging the ICM, or both.

Forgot to check the temp with my IR gun.

Thank you all for the advice. Will update the thread as needed.

 

[Fun Times]

My suggestion is only meant for only when/with the engine off is when you could try disconnecting the ICM as it's not seemingly safe to do so while the engine is running.

You may want to try one more time too see if the next trip out is better for you.