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mlteague70

1993 240 Signature 5.7L mercruiser voltage drops and engine dies

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I have a 1993 240 Signature 5.7L mercruiser alpha 2 outdrive voltage drops and engine dies at idle or under load. Sometimes is runs fine underway and it sputters and i watch voltage meter on dash drop and then it goes backup to over 12v and drops again and dies. I took the alternator off to test but the auto parts store couldn't test it. Does anyone think this is an electrical issue or fuel issue?

 

Thanks,

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  Check the water level in each cell of the battery. It should be covering the tops of all Lead plates.  Then try charging the battery. What type of chemistry is the battery ?

How low was the water in each cell ?  Are there WHITE CRYSTALS around each water cap ?  Corrosion on the metal posts of the battery.

Post some pictures of the battery & battery posts. Also of the big cable ends on the motor & starter.

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Sounds like you have a charging issue. I had very similar issue on mine that took a while to trouble shoot because it was intermittent. I replaced the battery thinking it couldnt hold a charge which it wasn't but failed because it was constantly being discharged and recharged all the time due to a failing alternator.  

Test the voltage at you alternator positive terminal first and work you way to batteries. So alternator, wiring to battery isolator, voltage at isolator, wire to battery, then battery.  Running the voltage should be about 13.4 V at alternator and 13 v at isolator ( drop in voltage normal on a isolator) its essentially a bunch of resistors. 

Hope that helps

 

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My alternator was intermittent and when the batteries were fully charged they were reading over 12 v so it was hard to tell the alternator wasnt charging . Also the isolator and battery switches allowed either alternator to charge both batteries. So I would get close to same volts not realizing other alternator was trying to take up the slack.  Had to disconnect wire from alternator and then test to get a true reading.......tricky.

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