Engine shuttering with loud noise

[BigN8]

Weird occurance today. Floated for about 3 hours no stereo. When I started the port engine the battery seemed dead, engine turned over sluggish. Then started stbd. Same thing. As soon as stbd cranked the port engine started shuttering and make a knocking noise. Check engine alarm came on. I shut both down. Check engines. Nothing seemed wrong. Then I started stbd first then port. Same thing sluggish start but this time stbd shuttered and made weird sound followed by check engine light. So I shut stbd down and started to lp back on port since it was running fine. Just for the heck of it I tried restarting stbd after about 1 minute. Started fine and ran fine. Tried cruising at 30 mph no problem. So I let it idle for about 20 minutes while I removed the bow ladder. I started thinking I've got a bad battery and the low voltage start some how messed up the engine on start. I shut down engines and then switched battery selector to 1&2. Then cranked both engines. Both started perfect with no lag in cranking and no engine alarm.

 

[Glassman]

I think you nailed it, battery.

Similar thing happened to me once. If I recall correctly, I started the port first and then it died when I tried to start the starboard engine - starboard ignition has all the accessories on my boat (fuel, depth, etc.)

So then I started starboard 1st, then port. No problem, but battery was at end of life. After new battery never had that happen again.

 

[Gym]

I believe the cause was low voltage to the ECU. The ECU controls many engine functions including fuel delivery via the injectors and timing. They were both messed up until the operating engine's stator built a little charge back in your battery.

 

[davel501]

Matches my experience with dead batteries. Have to let 1 engine run a bit before trying the second to build up a little power.

 

[BigN8]

Thanks for the confirmation guys.

 

[Bruce]

@jawsf16 had the same issue with a bad battery yesterday

 

[Zarrella]

I'm having the same issue today. But my batteries are seven years old so I can't complain

 

[jawsf16]

@jawsf16 had the same issue with a bad battery yesterday

Yep. But it turns out that battery was fine on the tester. I am thinking I had a loose terminal connection. It was intermittent but definitely turned the motors into "rocks in a paint shaker" mode. Very disturbing. Tightened everything up and ran perfect all day. On the upside I did get a spark plug change knocked out on the water while troubleshooting..,

 

[Ronnie]

My 06 waverunmer with 140 hp mr1 acted the same way a few weeks ago, that is, started but threw am alarm/warning a fee moutes in and died a few minutes after that. Ended up being a bad battery (very low on fluid and not charged / maintained in a few weeks). Switching that out was all it took to resolve everything. These things have very particular power requirements.