How often are alternators replaced, just to find out it was something else?

  • >70%

    Votes: 0 0.0%
  • >40<70%

    Votes: 0 0.0%

  • Total voters
    2

1997 Boat Owner

New Member
Jun 3, 2018
6
Boat Info
1997 330 Sundancer
Engines
2 X 7.4L Mercruisers w/V-drives
Took my '97 SR 330 DA for a shakedown ride. Everything great for 45 min's. Slowed to idle for no-wake zone and port engine shut off. I could restart it, but the only way to keep it running was to goose throttle and keep rpm's above 1600. Cursed. Turned around. Limped on 1 screw. Restarted port motor, put in forward in an rpm dip, ran the boat at 3200 back to dock. Ran smooth and strong (full rpm at full throttle,etc.) Died again once off plane. I believe the problem is voltage related. Voltage at the house and port batteries when idling is either 13.9 or 12.4. Sometimes it gets power from alt, sometimes not. Can't pinpoint conditions that lead to it not working (warm/cold/etc.) Checked wires, connections best I could. New batteries. New carbs. New fuel filters, fuel. New ignition parts. How likely is this the alternator? Does anyone know if the stock merc alternators have internal voltage regulator? Other ideas? Starboard engine perfect (has its own battery and alternator.) Does typical charge setup keep one side from helping the other?
 
You say these are carbed engines. Sounds like the port motor may be flooding and stalling due to too much fuel. Just because the carbs are new doesn't mean they are OK. I doubt the alternators are to blame on a carbed engine. The will have internal regulators and have for many years. I would start will checking fuel pressure with a mechanical gauge. Those electric fuel pumps can be a PITA.
 
Did you check the voltage leaving the alternator? If it's good there, and not at the battery, problem is in between. Remove/inspect/clean/reinstall wires. If still no good, replace wire.
 
I haven't checked the voltage at alt. I couldn't do it myself/ need a better volt meter. With respect to the carb, I am confident it's spot on. Fuel delivery should be fine as it can reach 4100. When it dies it drops way down in rpm and may take a few seconds to shut all the way off. No smoke or back fire or unburned fuel smell. Just fades out. Engines both idle at 600. I believe they are completely separated and use and charge their own bank.
 

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