1987 OMC cobra 3.0L, Charging system

[witt20]

Now that the fuel issue is resolved, now my newest dilemma

We finally got the boat to run for 25-30 minutes when it started stuttering and stalled. When I tried to restart it, the battery was low. I went back Weds and tried to start it, and the battery again was low so something is up in the charging system. I charged the battery up overnight and will be going back to the marina today to start it up.

Any expert advice on where to start and how to go through troubleshooting this? I have an idea but figured there was an order to follow..

 

[HT32BSX115]

Re: 1987 OMC cobra 3.0L, Charging system

Now that the fuel issue is resolved, now my newest dilemma

We finally got the boat to run for 25-30 minutes when it started stuttering and stalled. When I tried to restart it, the battery was low. I went back Weds and tried to start it, and the battery again was low so something is up in the charging system. I charged the battery up overnight and will be going back to the marina today to start it up.

Any expert advice on where to start and how to go through troubleshooting this? I have an idea but figured there was an order to follow..

Howdy,

I live a couple blocks away from an Autozone. I would just pull the ALT and have them test it.

If the ALT is ok, I would look for loose connections and/or loose or corroded ground connections.

You can also use a simple DVM (digital volt meter) to check the alt. If the operating voltage doesn't increase to about 13.5 or more volts the ALT is probably defective if all teh connections are clean and tight.

Cheers,


Rick

 

[framie]

Re: 1987 OMC cobra 3.0L, Charging system

i would use a volt meter and put the neg lead on the neg batt post and the post lead on the big red cable that is on the back of the alt and you should have atleast 13.5volts if not alt need replacing. also make sure connections are clean and tight. if you have 13.5 volts you need a new batt due to a bad cell.

 

[witt20]

Re: 1987 OMC cobra 3.0L, Charging system

Nah, battery is strong.

I will check for 13.5ish and if I dont have it, pull the alt and have it tested.

But who knows about replacing brushes in these older alternators? What other replacable components could it be? Anyone done a step by step diagnosis on one of these? I do have a digital volt meter and an ammeter as well (but I need a refresher on how to use the thing)

 

[HT32BSX115]

Re: 1987 OMC cobra 3.0L, Charging system

Nah, battery is strong.

I will check for 13.5ish and if I dont have it, pull the alt and have it tested.

But who knows about replacing brushes in these older alternators? What other replacable components could it be? Anyone done a step by step diagnosis on one of these? I do have a digital volt meter and an ammeter as well (but I need a refresher on how to use the thing)

You can easily check the battery voltage with the DVM. If it's charged, it will read around 12.5V or so.

After you start the engine, the voltage should increase to above 13.5V when the engine is at idle or above. If it doesn't, then you have a problem. ALT or connections etc.


Yes, you can replace internal components. and if you do a simple search, you can find instructions (and videos etc) on how to rebuild an ALT. I also saw a link for getting a rebuild kit.

I wouldn't waste my time though. You can buy a new/rebuilt marine alt on ebay or take it to a rebuilder usually, for less than $100.