Alternator?

J

JBFins22

New Member
May 14, 2013
48
Seekonk, MA
Boat Info
280 Sundancer 2004
Engines
4.3 MPI Mercruisers w/Alpha Drives
Returning back from lunch today everything was going great until I came down to idle. Starboard engine started idling very low (300-400) It ended up stalling. I tried to start it back up and the battery would only turn it a couple times. Now this sounds like the alternator went, ran the battery down, and stalled when out of juice. The boat is at the dock and the charger should be doing it's job. Guess tomorrow I'll see what happens. On a side note, the starboard engine has its own battery and that's all the battery is used for. The batteries are Northstar AGM and were brand new this year. Any advice will be appreciated.

Evan
 
when motor is running you should see around 14 volts if the alternator is putting out voltage.Your dash gauge should show this.Could be a lose connection
 
Thanks for the replies! I don't have a volt meter. I'm heading there in a little to see how the battery is charged and to see if it'll start. When I start it i'll look and see what the gauge says. Before the trip yesterday it was fine at about 14 so i'm hoping to see a drop....at least this will give me a definitive diagnosis, right? I'm also going to take it off and have it bench tested and possibly rebuilt. I found a genuine mercruiser part for $275 at boats.net
 
This morning the battery is totally charged and the engine barely turns over. I cleaned the terminals (even though they looked perfect) and it turns just a little and pauses and again. I'm thinking its a starter issue. Crawling down there now.
 
I found a genuine mercruiser part for $275 at boats.net
+
Made in Mexico

Check the cable connections at the starter AND at the engine block first
a quick test is to turn the ign on, look at the volt reading, start the motor , rpm at 1500 and look for an increase in voltage
 
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Check for loose or corroded wiring. I had a wire come loose. A loose wire will cause alternator to burn up a diode.
A good rebuild shop will find this and the cost of a diode is about $10.00.
Just something to check and may save you the cost of a new/rebuilt alternator.
 
JBFins22 said:
Returning back from lunch today everything was going great until I came down to idle. Starboard engine started idling very low (300-400) It ended up stalling. I tried to start it back up and the battery would only turn it a couple times. Now this sounds like the alternator went, ran the battery down, and stalled when out of juice. The boat is at the dock and the charger should be doing it's job. Guess tomorrow I'll see what happens. On a side note, the starboard engine has its own battery and that's all the battery is used for. The batteries are Northstar AGM and were brand new this year. Any advice will be appreciated.

Evan
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Does your boat have a parallel switch? If not you can use jumper cable to start.
If alternator is bad you can disconnect battery and engine will die as engine once started will run without battery. If engine continues to run, alternator is ok. The engine will run off battery without the alternator until battery goes dead. I hope some of this helps.
 
OK so after the battery charged all night and it's reading over 13 volts on all 3 (the one for starboard engine is isolated) the engine still only turns very slowly a couple of times, but this morning after trying it a few times i can hear an arcing sound and i caught a whiff of electrical smoke/burning smell. Every connection I checked was tight and from what I can see they are clean. The starter solenoid is hot and its getting juice. It's not the alternator at all is seems. This sounds like a starter problem or an engine problem (poss hydro lock?) not letting the engine turn over steadily and fast enough to start. After all, why would it be running at 300rpm after cruising at 3500 for 20 minutes?? It could be that the IAC i replaced 6 weeks ago is bad and not working right and just be a coincidence. I called the mechanic before I go down the wrong road.
 
Yes I tried the parallel switch and there was no change. My battery charger has a test button and it shows all 3 as fully charged. I didn't check this yesterday and I'm thinking since it's the same this morning that the battery never drained in the first place.
 
I think it's time to pull the plugs and verify or eliminate water in 1 or more cylinders - that could explain these problems. Plus, if you do have a water / hydrolock issue you need to address it ASAP before major damage is done.
 
BillK2632 said:
I think it's time to pull the plugs and verify or eliminate water in 1 or more cylinders - that could explain these problems. Plus, if you do have a water / hydrolock issue you need to address it ASAP before major damage is done.
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As I was thinking more about it this morning I though it was a possibility. Man I hope it's not that. This is the 3rd season on these manifolds, risers and elbows. Really hope that's not it.
 
Yeah I hope it's not water intrusion also, but it's a pretty easy thing to check for and hopefully you can start focusing on what the real issue is. If you find a plug or two wet with water or fuel andthe engine cranks fine without the plugs then you have found the problem.
 
Without properly testing any of the batteries or charging system your just going to throw money at it. Start with a volt meter. Your all over the place here and getting no where. Or have someone come in and look at it.
 
Batteries are fine. I can't test the charging system because it won't turn over fast enough to start. I'm waiting to hear back from the mechanic to have him take a look. I'm really thinking I blew a gasket and have water in some cylinders.
 
Turns out my suspicions were correct, unfortunately. Found water in the 3 right side cylinders. Head was pulled and valves were removed. Found a 2" crack above one of the intake valves. Time to break out another... After installing a new head, some serious flushing, and oil changes it should be up and running by this weekend.
 
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