intermittent alarm

jwells02

Cadet
Joined
Mar 18, 2013
Messages
15
I have a Mercruiser 5.7 2001 with a bravo three and i get an intermittant alarm. Fluids temps and pressures are fine. I notice a slight loss of power during and after the alarm but it recovers after a few seconds. The schenatic is skmple. power runs thru the alarm and then goes to each sensor where if one grounds the alarm sounds. I cant connect the problem with a slight power loss which seems like loose one cylinder. any ideas
 

alldodge

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Mar 8, 2009
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With power reduction I'm going to guess its EFI, how about a serial number?

If the motor is picking up a knock then there could be a power reduction happening.
 

jwells02

Cadet
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Mar 18, 2013
Messages
15
It is carborator. There is no knock. I will get the ser# as soon as I get back to the boat.
 

Fun Times

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Since there seems to be a power loss, Make sure all the power electric wires are clean and tight and also using a multimeter, check for loss of 12 volt power such as the alternator as you may have an intermittent power loss or short circuit going on possibly causing the beginning key on alarm to sound intermittently.

Also try disconnecting both wire harness connectors going to the thunderbolt 5 ignition module and ensure the wires and pins on both sides are clean and not backing out of the connector.

Plus next time you're on the water and the warning horn sounds, try disconnecting the wire connectors to the ignition module seen below for a minute then run the boat again and see if the warning horn turns off. If not, disconnect the engine temperature sending unit with the yellow and black wires and run the boat. Then disconnect the 2 wires going to the gear lube reservoir....If not then there's only two things left which would be the engine oil switch or a short to ground on the Tan/Blue wire somewhere a long the line.


861251A1_2_site.jpg
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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your 2001 should have knock sensors on the TB-V.
 

jwells02

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Mar 18, 2013
Messages
15
Very difficult to troubleshoot because it occurs intermittently at speeds above idle while underway. The slight reduction in power is throwing me. Since this wiring connects through the electronic ignition does an alarm reduce the power intentionally through the EI somehow?
 

jwells02

Cadet
Joined
Mar 18, 2013
Messages
15
I've been reading some systems reduce power on alarm. Not sure if it applies to mine. It appears the best place to start is to disconnect the sensors one at a time and run it to see if the alarm goes away. With the sensor wire going to the EI is there a condition where the EI would sound an alarm?
 

alldodge

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Mar 8, 2009
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If your motor starts to knock you may not hear it, this is the reason the motor has a knock sensor. The sensor can also be defective and cause the issue. If the Blue wire is routed to close to the spark plug wires it can set a knock fault in the module. Here is how its tested

TB5 Knock Testing.jpg
 
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