I would not attempt to diagnose a 496 with a video. http://www.rinda.com/marine/marine.htm#merctool will be the best money you ever spend on that motor.
If it's beeping, 99.9% of the time, the computer is trying to tell you what's wrong. Listen to it before you start replacing things and wasting time, money, and effort.

Good advice....I bought the Rinda after the first problem I had, money well spent. I figure I spend more money in fuel for a weekend the that scan tool costs!

Just the logistics of towing your boat to a mechanic once or twice to have it scanned...
...is worth it to own the scanner yourself.

Share the cost with a few neighbors or local boaters with the same motors. You can buy multiple pigtails for just about any Mercury/Mercruiser computer including outboards.

Thanks Reckless32 however we have no alarms. We suspected an exhaust leak and found a bad manifold
Gasket and riser gasket.
Could this cause a guardian response????

Hello All,
I replaced the IAC and went out to the lake this week. First day ran perfect all day. The second day boat started rough off trailer, I shut down then restarted again ran fine. About the third boat ride of the day I was throttling back going into a cove and the motor shut off. No beeps, alarms, etc. Would not start back up. Took to the mechanic and they ran the scanner, no codes.... They did a misfire test and found the #5 cylinder not firing.Changed spark plug and problem fixed, so says the mechanic. I wont be able to test till next Thursday.
Any tips or advice I don't think that would cause the motor to shut down, ???

Have you verified that you have no loose connections on your ignition interrupt switch? (lanyard kill switch) Same goes for your ignition (key) switch(es).

I will check them when I get back out to the boat, it is out in Bullhead currently. The mechanic stated that he checked all of these, he also unhooked the harness and re-greased. Man this issue is wearing me out I have thought several times I and the (forum) have had this figured out.
Thanks Sydwayz.

That sucks, when you pulled the old IAC out did it look like there was any melted plastic on the plug or coming out of the little actuator? The ECM on the 496 is really good at keeping the motor running (that goes for most EFI system as well) under all sorts of conditions. I am not sure that a misfire on 5 would cause it to shut down and not restart coming off plane. I am with sydwayz, kill switch ignition switch, loose plug on the ECM, maybe chasing two different issues. Funny that on a new IAC it ran fine all day next day issues come up again. Back to a fuel issue, what was the fuel load day one vs half of day two when problems came up?

There was no melted plastic on the old IAC, but the spring was gone. The fuel load on day one was full two 40 gallon tanks, the second day there was a little over half in each tank. I tried switching tanks and also played with the kill switch no luck. Another one hour tow back to the marina....

Could be a loose connection, wire rubbing, broken wire. Do a "wiggle test". With the engine running start moving, pushing, pulling, shaking all the wires and connections. See if the engine reacts when you are doing this.