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High volts showing on dash meter and occasional low performance from engine

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In the spring while getting my boat ready for the water I hooked the battery up backwards.  It was only for a split second because it popped and sparked which made me pull the wire back.  I know, I know, I'm dumb for doing it.  I then hooked the batteries up correctly and later went to use the boat.  When I started the boat the screen showed a warning that read "Voltage above normal or shorted high."  I acknowledged the alarm, took the boat out on the water, and then noticed that the engine would only rev to about 3000 RPM's, even if the throttle lever was all the way forward.  I then turned the boat off at the dock and then started it up and went back out.  This time the boat would rev like normal.  I called a Malibu dealer and spoke with a mechanic who asked about the engine volts.  I checked  the dash and discovered that the volts would go up to about 15.2 and stay there.  Took the boat to the dealer and they installed a new alternator and throttle lever assembly.

Got the boat back and the volts seem to stay at around 15.0 and occasionally the boat will not rev as high as it should.  Sometimes it will rev up to full speed like normal but the volts are always around 15.0  or a little higher.

Thinking that maybe I smoked a battery when I hooked them up wrong I tried a different battery that I knew was good.  Nothing changed.  The mechanic at the dealer didn't have much else to offer over the phone but did say that the 15.0 volts is too high.

Does anybody have any idea what could be wrong with the boat?  Any ideas about eliminating possible problems?

I'm assuming that the alternator and throttle lever assembly was installed correctly since it was done by a Malibu mechanic. 

The boat is a 2011 Malibu Wakesetter VLX with the 350 Monsoon.  There's about 230 hours on the boat.

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Is the voltage high all the time, or only when the engine is running?  It doesn't make any sense that it would be high with the engine off.  Are you using a separate meter to verify voltage? 

And by the way, the battery is probably the only thing you *didn't* smoke. 

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2 hours ago, justgary said:

Is the voltage high all the time, or only when the engine is running?  It doesn't make any sense that it would be high with the engine off.  Are you using a separate meter to verify voltage? 

And by the way, the battery is probably the only thing you *didn't* smoke. 

Those voltage numbers I gave in my original post was what the voltage meter on the dash of the boat was reading.  So no, at the time I wasn't verifying with a separate meter.  And yes, the voltage reading at the dash was only high when the boat was running. 

Since then I've tested it with a multi-meter.  While the boat is running the dash of the boat will read around 15.0 volts but the multi-meter at the battery will read about 14.4 volts.  It appears that the volt meter in the dash of the boat is consistently about .6 volts higher then what the multi-meter reads because when the engine is off the volts at the dash read 12.9 and the multi-meter at the batteries reads 12.3.  Is 14.4 volts good or is it still a little high?  I'm getting mixed messages on that.

I did have the batteries checked by a professional, and not just with a multi-meter.  He did confirm that the the batteries were good.  So you're right there. But what else do you think I could have smoked?  The main computer on the engine?  Computer in the dash?

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14.4 is about right to charge a lead-acid battery.  I think your charging system is ok now, but it is hard to tell what other problems you might have. 

Anything electrical (DC at least) does not tolerate reverse voltage well.  Typical protection includes a diode that prevents damage to the rest of the circuit.  Many times the diode is sacrificial, and must be changed after a reverse voltage event.  Sometimes the diode is beefy enough to survive. 

Since you say things work correctly sometimes, I'm going to hazard a guess that the reverse event caused a wire to make poor contact somewhere, and it occasionally acts good enough to work.  Check all of the connections you can find that have anything to do with the engine or dash.  Check means open the connection, inspect carefully for damage (melted contact, etc.), and reconnect.  This includes screw lugs on a terminal strip and plastic connectors.  Everything.  Also look along the wires for signs of melting. 

It took me about an hour to do that under my dash, but that was mostly just the terminal blocks.  I also did the engine grounds and cannon plug. 

If I'm right, things will start working again when you find the right wire.  It's best to just do them all to improve your odds of finding it....

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Okay.  Thanks for the advice.  I'll do that when I get to my boat.  It'll take a while, but it's worth a shot.

The only thing that's not working quite right now on the boat is the throttle and the wedge.  The wedge issue might not be be related.  But the dealer said that when his computer was hooked up to the boat he could see that the amount of throttle was occasionally reading different at the throttle then at the engine.  He gave the example that the throttle might show 70 percent and the engine is only reading 30 percent.  That's why they changed the throttle; thinking that I ruined the throttle (sensors/potentiometer) when I hooked the batteries up wrong.  But since the boat has the same issue with the new throttle assembly I'm thinking that maybe I burnt up the computer on the engine too.  Or only the computer on the engine and my old throttle was actually okay.  Thoughts on that?

And thanks again for the advice on checking the connections.

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I think if it worked ok, the electronics are working.  You would either kill a part or not, with not much chance of anything in between. That's why I'm hoping you have a loose connection somewhere. 

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Well... I guess I didn't consider that before, but that does make sense.  Just gave me a little bit of hope. 

So I'm hoping that's all there is to it too.  I'll keep you posted.  Thanks for the help.

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