Mercruiser runs great then after 10 min misfires and alarm sounds.

I have a 2011 Mercruiser 350 mag Bravo III. Taking on the water for the first time, things ran great. At 4000 RPM's temp normal, Oil Pressure Normal, engine was purring. Then after about 15 min the alarm sounded and the engine was misfiring. I immediately went to idle, and the engine sounded great, alarm was off. I then ran it up to about 2000 RPM's, everything seemed fine. After about 10 min I brought it up to 3500, and again things fine...then after about 5-10 min, same thing...alarm sounded, engine hesitated. Went to idle, and no issues. Ran at 2000, no issues...after 10-15 min brought her up to 3000, no issues for 5-10 min at that RPM's then the same thing happened again. Any ideas?

Thanks
Mike

What's the temperature and the oil pressure of the engine when the alarm goes off?

Mine did that exact same thing and it ended up being the IAC valve. On my engine it’s on the top of the engine and very easy to replace.

too much oil , aerating/foaming
too little oil
too thin from heat
temp sender/gauge inaccurate and running hot

How about posting a serial number.

IAC will not cause this unless the IAC shorted then melted and damaged the ecm.

mechanicman said:

What's the temperature and the oil pressure of the engine when the alarm goes off?

Click to expand...

Normal...when alarm goes off and when at idle.