Merc 4.3 Stalls At High Rpm...

[MariahSX20]

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 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?

 

[MariahSX20]

Re: Merc 4.3 Stalls At High Rpm...

Anyone willing to take a shot at this one...? ? ?

 

[Haut Medoc]

Re: Merc 4.3 Stalls At High Rpm...

Are you sure that hitting that reset button is really doing anything?......
I would be looking at the battery terminal connections on both ends for cleanliness.....
That means taking them apart & making sure that they are free of corrosion.....
Does the trim work when everything else is dead?.....
I would also check the plug where the engine wiring harness meets the instrument harness for tightness & cleanliness, I have a light coating of dielectric grease & a hose clamp on mine to keep it tight & moisture free....
You will need to get it running & do the 'wiggle test' on all of the connections.....​

 

[MariahSX20]

Re: Merc 4.3 Stalls At High Rpm...

Indeed Haut Medoc, I am positive that only after I resetted that fuse I got current flowing again and was able to bring back the engine alive. Both battery terminal connections are clean and in good shape. I did check all electrical wires and connections on the boat and all seem in good working order.

I am new to boat engines and this might be ignorance from my part, but I noticed something that seems a bit strange to me. Being my boat electrical system is 12V, I ran the engine at idle (700 RPM), and the Battery Voltmeter gauge read 14.2V. Then, I turned every switch ON (lights, pumps, radio, etc.), it drops to 14V and won't go any lower. Is this completely normal and what the correct gauge reading should be, or shouldn't it be closer to the 12V mark? I could be wrong but I might have a bad alternator, do you agree?

 

[Don S]

Re: Merc 4.3 Stalls At High Rpm...

Battery Voltmeter gauge read 14.2V. Then, I turned every switch ON (lights, pumps, radio, etc.), it drops to 14V and won't go any lower.

Once you get the rpm up a to around 2K, you will see even higher voltage. Between 14.5 and 14.8 V is where the regulator is set for max charge. It's very normal, Even on cars and trucks) that is just what they are.
Actually if your battery shows exactly 12V, it's almost dead. A fully charged batter after setting should be in the vacinity of 12.6 to 12.8 volts.

What you need to do is use an amp meter to find the amount of amperage that is kicking that breaker. Kind of a pain I know, but that is how it's done. Or, you can change the breaker. I have changed several of them that pop for no reason and never have high amperage in the system to pop them.
Once changed, no more problems.

 

[MariahSX20]

Re: Merc 4.3 Stalls At High Rpm...

Don, I do really appreciate the information you provided me.

Now, when I test the breaker with the multimeter, what kind of reading should I be getting to know the breaker is indeed bad and needs replacement? Sorry if I lost you somewhere, but I'm not quite sure how to go by to accomplish this. (The breaker in question is a 50 amp fuse). I'll hate to spend $50-60 in a new breaker to find out the breaker was not what was originally causing my problem.

Thanks again!

Kindly Andy