Alternator/Starter/Battery Issues - Mercruiser 350 Mag Mpi

[MizzouWake]

Was hoping for some troubleshooting tips or past knowledge from someone on this board.

The issue with my boat is it "appears" that the batteries aren't holding a charge and/or the boat's starter or alternator is malfunctioning.

My boat is a 2004 Tige 21i Riders Edition direct drive with a 350 MerCruiser Mag Mpi. I have two batteries with a battery selector switch currently set on 1+2.

We took the boat to Bull Shoals Lake over the weekend just after a recent Wetsounds Rev 8/Syn 4 install which also added the 2nd battery.

The boat ran great all day Saturday, no issues. The boat ran great all day sunday until late sunday evening when I couldn't get it to start after turning the engine off. All I would get was a "click" noise, no cranking. The batter gauge was showing less than 12V and eventually decreased to nearly 10V. The interior lighting, stereo system including wetsound tower speakers, and nav lighting all continued to work.

We thought that somehow we had ran the batteries dead even tho we basically just cruised around the lake wakeboarding/surfing with little to no time with just a stereo running without the boat running as well. We put it on a charge overnight and it started right back up this morning. After running it maybe an hour, turning the engine off, same thing....it wouldn't turn over.

My father in law who is pretty savy with engines etc thinks it's either a bad alternator (not keep batteries charged), a bad starter (dragging once it's hot after running a while), or a dead fault/short in some of my new wiring for the wetsounds that might be draining the batteries.

The one odd thing is that once it wouldn't start today, we trailed it and drove the 5 hours home. Once home, we put the key in and it turned over fine. We tested both batteries with a volt meter and it came up 12.43 V, plenty of voltage for cranking the engine to life.

What does this sound like? Where should we start when trouble shooting? Alternator? Starter? Bad Wiring? Something else??

Any help is appreciated!

[chpthril]

Did you guys do the recent audio/battery upgrades or did you have a shop do it? If you had a shop do it, dont sweat it, just arrange for them to get it back in and test it. Just make sure they have the means to safely run the engine, whether on the trailer or dunk it in the lake.

If you did the upgrades, then you will need a digital volt meter.

[MizzouWake]

I had an installer do it for me but I had had some minor battery issues not keeping charged before the install. Nothing to this magnitude tho...and these are new batteries.

Any way to rule out starter/alternator?


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[chpthril]

Yes, the alternator and starter can be tested with them in place. A volt meter can test the alternator's output from the alt all the way back to the batteries. Along the way, you can determine if the switch is wired ideally.

To fully test the starter, you will need an amp clamp amp meter along with the volt meter. The volt meter will tell you you are getting voltage in the right places, but the amp clamp will tell you how many amps the starter peaks at and then levels off at. Too high indicates a failing starter.

[boatwakes]

Shake the shifter in neutral while holding the key to start, sounds like neutral safety issue. And check tightness of connections at batteries and ground to the engine.