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Merc 43 Stalls At High RPM

mariahsx20

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"My 2006 Mercruiser 4.3L Carb

"My 2006 Mercruiser 4.3L Carb 190HP I/O ran fine for about 45 minutes before dying/stalling out while underway and without warning at about 1800 RPM. I tried to start up the engine but it was completely dead; no engine cranking sound, no audio warning alarm either. I checked all electrical gauges and all were out. I then checked all battery connections, fuses, wiring, etc and all seemed normal. I resetted the big, red "Reset" button for the electrical overload protection system and the engine started up OK. I turned around back to port and engine ran fine for 10-15 mins, but it stalled again at about the same RPM and conditions as before. After resetting the overload electrical system breaker for a second time, the engine finally restarted and I was able to get safe to port but only at a very low RPM and minimal, almost idling speed.

Any idea what might be causing this guys? :-?"
 
Andy:

That is a 50 amp br


Andy:

That is a 50 amp breaker so something electrical is seriously failing. Get the alternator and battery checked out. Do you remember what the voltmeter was reading?
 
"Also, is / was, your starter

"Also, is / was, your starter hung up and running all the time (could be hard to hear if engine running)? That by itself could explain a heavy electrical drain and (sometimes) crippled engine performance."
 
"Thanks Guy and David for your

"Thanks Guy and David for your replies.

The voltmeter reading was close to 14V. I just ran tested the engine today and the volmeter read 14.2V @ 700 RPM, and dropped to 14V with all electrical switches ON (radio, pump, lights, etc.) @ 1200RPM. Are these normal readings for a 12V system? The battery is brand new, so I am thinking also that I might have a bad alternator.

David, I am not sure if the starter was hung up or not. Like you said, the engine is fairly loud and I couldn't tell, but I'll look into that possibility as well.

Thanks kindly, Andy"
 
""volmeter read 14.2V @ 70

""volmeter read 14.2V @ 700 RPM, and dropped to 14V with all electrical switches ON (radio, pump, lights, etc.) @ 1200RPM. Are these normal readings for a 12V system?"

You can't ask for better voltage readings than that! Your alternator is fine. Make sure your battery cables are tight on both ends including the trim pump wires on both ends which draws alot of current."
 
"Guy, a friend at work told me

"Guy, a friend at work told me that the reading I'm getting of 11V (engine/elect OFF) is too low and points towards a bad battery cell..do you agree?"
 
"Ahhh,, new data... [ 11V &#40

"Ahhh,, new data... [ 11V (engine/elect OFF) ]

That is too low for a supposedly charged new battery, and can cause some electronic ignitions systems to kick out! Could definitely cause engine to drop speed, but to date I have never seen a low/failing battery cause the 50 amp breaker to trip.

Alternator seems to be putting out well, but if fighting a failing battery it can not put out enough to maintain high engine speed also. 1800 rpm is marginal speed for running off alternator only. Is the drive belt really tight? Slipping belts can cause all kinds of irratic problems.

Swap the battery with known good unit for at least a test run on this item. 'New' battery does not always equate to 'good' battery.

For what it is worth, over the years I have had similar problem. And in a couple of cases caused by failing batterys and in one case by failing alternator. So keep checking deeper."
 
"Andy:

David is correct in


"Andy:

David is correct in his statement and your friend is right. A fully charged battery should read about 13.5 volts. If you have a hydrometer, you can insert it into each cell and check its specific gravity. One of your battery's cells will read on the low end and the acid will not be clear but darker. Or you can get a tester that looks like a 5 ball antifreeze tester that tells you the amount of charge in each cell; they should all be nearly equal.

Batteries are made w/date codes on them. A code like G7 means it was made in July 2007. Don't buy one that is more than 6 months old."
 
"David:

"I have never s


"David:

"I have never seen a low/failing battery cause the 50 amp breaker to trip"

If the plates in one cell are cracked, vibration can cause them to separate which then puts the full load on the alternator until the plates make contact at which time there will be a current surge."
 
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