Voltage Low - - HELP!

Ok I had posted a similar question to this in another thread but I believe it would be better served here with a better question...


I have a 97' Moomba Boomerang... the Voltage meter is reading very low right at 12 or below... so when I idle down it doesn't produce enough voltage and it dies... Medium to top end runs perfect.

I have put in a new coil... had the alternator checked... nothing at all wrong with the alternator, it's perfect...

I just had a new CD player installed and I was wondering if that could have anything to do with it?.... This never happened before the cd player was installed... or is there something else I need to be looking for?

PLEASE HELP!

it is clear that the alternator produce less than the system demand at idle so start disconecting things while looking at the voltmeter and you should be able to find the over consuming component.

start by disconecting the amp(s) form the battery pole...

Can you please be a little more elaborate? I am not sure what the amps are from the battery pole? I am very clueless at this sort of thing... :confused:

If you are referring to an audio amp for a sub... it doesn't have one.

amp = amplifier

Your sound system must be wired from the battery whit a big wire with a fuse on it. If you can find this wire, disconect it from the pole so it is offline...
Run the boat and see if your alternator is now pulling enough power to maintain the ilde.

oh... no amplifier, so i guess no big wire...

Just unplug the Head unit then...

Are you realy sure the alternator is top shape? A weak alterator can produce 20 amp at 2500 rpm an drop under 10 amp at idle... The engine need 16 amp to run if i remember...

It had an Alpine CD player in before and I didn't have this problem... had a brand new SONY installed and it has started doing this... do you think that this new CD player could really be causing the trouble?

Bringing my voltage down that much?

I had the alternator taken off put on a machine and checked... said it was good as new.

Probably not...
If the problem still ocur with the head unit turned off, your probably looking for a short circuit

Is your battery dead?

A new batter was supposed to have been installed at the beginning of this summer... can it still run good thru middle and top end with a dead battery?!?!?

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Originally Posted by Lakeside09

A new batter was supposed to have been installed at the beginning of this summer... can it still run good thru middle and top end with a dead battery?!?!?

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yes. When the engine turn, the alternator produce all the current the boat demand (motor + accessories + recharge for the battery).

So if the battery is bad... then when I start to idle down it will lose voltage and die... but crank and start again fine... try to give it some gas to take off it will try to sputter out... but if I give it hard throttle... it will run perfectly fine... until I start to idle down again... then it will die.

So it may be the battery?

Im pretty sure its not the battery because you had enough power to crank again and again...

Do you know for sure this is electrical? Are you fue injected?

The symptoms you describe can also be attributed for a faulty Idle Air Control

first i would put a voltmeter on the battery while at idle to see actually voltage because mayber your voltmeter in dash is a little off and you really do have a engine problem.

if voltage is 13.5 or more i'd say its not a charging problem.

if its really only 12 or so then you would then check voltage starting at the battery back towards the alternater and might find a bad connection or wire.

I had a bad charging wire in the wire harness on a previous boat i needed to replace

just my 2 cents

Yes it is Fuel Injected... Where would I look to check to see if it is the air idle control? Is this expensive to fix... If that is the problem?

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Originally Posted by Lakeside09

Yes it is Fuel Injected... Where would I look to check to see if it is the air idle control? Is this expensive to fix... If that is the problem?

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The Idle Air Control is usually right at the intake plenum. it is basically a solenoid valve that opens and closes to allow a small amount of air past the butterfly to keep the motor running. It will be a small device with a wire, (maybe two) that is bolted right to the side of the intake, under the spark arrester.

The redneck/shade-tree way to check it is to tap on it with the handle of a screwdriver, not too soft as to do no good, but not so firm as to break it. If the IAC is acting up, many times banging on it will loosen it up enough to get it to jump to a smooth idle. It will then probably rtun fine until the next time you shut off the boat and let all systems go cold, then the motor will run rough at idle.

Ok my original thought is that it was a fuel injected motor. It is not.


I took the water pump off and the impeller was torn and crumbled... could this be the cause? Installing a new one immediately.

Also could there be a leaky gasket causing it not to idle well? How would I check for this?

Or could the impeller be the source of my idle problem, as the water pump was not turning well...

I know this may be crazy but I just had it happen to me. Check the voltage witht he same voltmeter on you vehicle battery and see what it is. I have a bad voltmeter to cost me like 10 hours of work before I figured out the voltmeter was bad.