Alternator Failing?

2000 model Cummins 5.9 ltr 330 hp.

Sunday, while idling around waiting to join the fleet review parade at YC, I noticed that the voltage meter was down around 12 volts instead of the normal 13.8. Occasionally it would jump back up to 13.8 then drop again and when I increased the throttle it went to 13.8. When cruising at higher rpms it remains steady at 13.8.

Is it starting to fail?

Doc, Maybe and maybe not. You may start with checking all of the wiring connections followed by a check of the alternator using a quality digital voltage meter AT THE ALTERNATOR and then again at the gage. If you get a good reading at the gage but it still shows erratic readings, you may need a new gage. Look at the least expensive fixes first. Don't forget to check the belt tension. Chuck

-- Edited by Capn Chuck on Tuesday 9th of March 2010 09:27:13 AM

I forgot to mention that this engine also has a post heater in addition to a pre heater. When you first start it the voltage is drawn down to 12 until the engine warms up for a minute or so unless you increase rpms above 1000 or the heater kicks out.

Maybe the post heater kicked in idling around in the cool water?

Back to the alternator...do these things have stages where the low rpm diaodes? may be failing?

-- Edited by Doc on Tuesday 9th of March 2010 09:38:25 AM

-- Edited by Doc on Tuesday 9th of March 2010 09:39:01 AM

-- Edited by Doc on Tuesday 9th of March 2010 09:40:12 AM

We have the same engine, same year, same problem last season except voltage would drop to 11 or so and low voltage alarm would come on. Eventually, even at higher rpms, the voltage would not go up. Our local Cummins mechanic disconnected the preheater plug on the port side of the engine and we have had no problems since. A little dark smoke on start up. Mechanic said 90% of the local lobster boats disconnected this item for the same reason. There is a workaround of putting a dash mounted momentary or on/off switch in the circuit if one wants to be able to use the preheater but, since we use the boat in the warm months, we haven't gotten around to that yet.

I assume that you are saying that the pre heater plug and the post heater plug are the same?

Doc wrote:

I assume that you are saying that the pre heater plug and the post heater plug are the same?

Click to expand...

Dunno about that. I could show you a pic of the plug if I could get my bleeping camera to work.

Doc:

I also have a 330B and mine has been doing as you describe for 3 years. At cruise (2000) there is no fluctuation.

Dwhatty *has a bleeping camera. Mine doesn't bleep it's Japaneese it says CRICK

SD

skipperdude wrote:

Dwhatty *has a bleeping camera. Mine doesn't bleep it's Japaneese it says CRICK

SD

Click to expand...

Mine's Japanese as well and it neither bleeps nor cricks at the moment.

*

They are practically putting cameras in Cracker Jacks as a prize they are so cheap these days....go getchya a new one!!!!

Rupert the alternator repairman said to get my (_,_) down there and check the belt and the tensioner before pulling the alternator. Tomorrow maybe.

Generally, your first clue that it is the belt is that there is a lot of dust in the vicinity....a belt that is slipping will dust things up something fierce.

I pulled it yesterday and took it to Rupert. He wasn't there but his son said that it would be ready Monday.

There was no dust, the tensioner ran smooth and true with a new belt. I load tested the batteries and they didn't quiver. That's about all I know to do.

Rupert gave it back to me yesterday and I put it on today. Still does almost the same thing so I guess there was nothing wrong with it. He said that it will show lower volts at idle so as to not load the engine until rpm's are increased.

It got a good corrsion cleaning and a new regulator anyway.

Moral of story...if it ain't broke...