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Old 06-11-2022, 05:43 AM   #1
rwc
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Hi,

I have a newish 5.7L mercruiser MPI

A few weeks ago, I started the boat up to go out, then it choked and died. Started again, ran for thirty seconds then died. Third time, nothing at all ( no tone, didnít turn over, just silent). I traced it to the 50A breaker on top of the engine, which had popped.

I pushed the breaker back in and tried it again. It made a funny noise, like a bad connection, then turned over and started, but again died after 10-15 seconds.

So today I cleaned up all the connections between the battery and the starter, reconnected the battery, tried to fire it up and got nothing, breaker is in, but no tone or turn.

Any ideas what to try next?
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Old 06-11-2022, 11:08 AM   #2
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Measure to see if you have 12V at the breaker. No voltage check the fuse at the starter. Voltage check for 12V on the B terminal of the ignition switch.
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Old 06-11-2022, 12:45 PM   #3
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Thank you!

Sorry for the dumb questions, but does the key need to be turned when checking the voltage at those points? Is the fuse at the starter the one between the positive battery cable and alt cable?

Would a bad starter cause this? I had a flood during a storm in September and the starter was immersed in seawater. It worked fine afterwards, so I thought I’d got away with it, but I read your comment in another post that an immersed starter never lies (which I presume means it doesn’t survive).
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Old 06-11-2022, 03:16 PM   #4
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The key doesnít need to be on but the battery switch does. There is a 90 amp fuse on the starters solenoid that supplies power to the breaker. Very seldom will a submersed starter not fail in the near future.
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Old 06-11-2022, 05:21 PM   #5
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I get battery voltage on the larger lead to the 50A breaker and 10.4V on the other side. That doesn’t seem right. Bad breaker?

I’m assuming I should replace the breaker, replace the starter, and learn to moor better in storms?
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Old 06-11-2022, 05:31 PM   #6
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9.7V at ignition.

I can’t find anything I can reach on the starter that isn’t battery voltage or no reading, but it’s very difficult to see / reach with the battery in place, so might be missing the right spot.
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Old 06-11-2022, 05:53 PM   #7
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Quote:
Originally Posted by rwc View Post
I get battery voltage on the larger lead to the 50A breaker and 10.4V on the other side. That doesnít seem right. Bad breaker?

Iím assuming I should replace the breaker, replace the starter, and learn to moor better in storms?
Remove the wire from the 10.4V side to see if the voltage goes up, if not replace the breaker.
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Old 06-11-2022, 05:54 PM   #8
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Quote:
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9.7V at ignition.

I canít find anything I can reach on the starter that isnít battery voltage or no reading, but itís very difficult to see / reach with the battery in place, so might be missing the right spot.
9.7V on the coil is good as the wire is resistance and the voltage is prober. This also tells you the fuse on the starter is good.
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Old 06-11-2022, 06:08 PM   #9
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Remove the wire from the 10.4V side to see if the voltage goes up, if not replace the breaker.
Voltage went up to 12V with the smaller cable disconnected, so not the breaker then?
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Old 06-11-2022, 07:06 PM   #10
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Quote:
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Voltage went up to 12V with the smaller cable disconnected, so not the breaker then?
This is one of those that can go either way after thinking about it. If the breaker is resistive no load, wire removed can yield good voltage but add load and you get a voltage drop. Guess I would replace it.
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Old 06-11-2022, 08:16 PM   #11
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This is one of those that can go either way after thinking about it. If the breaker is resistive no load, wire removed can yield good voltage but add load and you get a voltage drop. Guess I would replace it.
Iíve got a spare starter, so Iíll start with that and see what happens. I think the breaker should be easy to get if the problem persists.

Mike, thanks so much (once again) for your help! Without it, I probably would not ever have a functioning boat.
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Old 06-27-2022, 02:17 PM   #12
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Just to close this one out, I had very corroded battery cable connections and the breaker would pop shortly after start up. After three or four times trying to track down the connection issue, I realized I’d missed a connection (the worst one). Cleaned them all up, but now no start at all.

Changed the starter to a spare, no effect. Changed the breaker as per mmwjr advice, and the engine fired right up. So guessing I must have cooked the breaker by overloading it too many times.
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