It's a real common problem on all the ECM/PCM555 engines. I believe that a lot of failures are caused by a restricted IAC muffler, which cause the IAC to run continuiously at 100% Duty Cycle and overheat.

Unbelievable. Port side IAC went bad on last trip out (4 weeks ago). Replaced it, all seemed fine until I went to do the 160 mile round trip to San Francisco Bay yesterday morning.

50 miles out the starboard engine started acting up in the same way, guardian mode, 2 beeps every 1 minute, etc. Had to limp home and am really p*ssed at myself for not replacing both IACs at the same time...

I will start carrying a spare on board.

I did the same thing I carry an extra one in my tool kit

Old thread different engine same problem.Constant alarm over 4000 rpms back off get the two beeps.
Before the season started did exhaust (Imco) new plugs impellers and thermostats.Good oil pressure running 170 where it always does and no codes.I am starting to think coil is breaking down or drive lube level sensor.
One weird thing though when boat was new the two inner baffles came out of the tips on the starboard engine so there is only one on each side.The port still has two and thats the engine that is throughing the alarm.I ask this because the Inco would not line up with the Y-pipes so I went strait through hull.Doubt small blocks with 4 inch exhaust could have a back pressure problem but I am at a loss right now.Might cut the baffles out tomorrow or just start throwing parts at it.Any thoughts?

I already changed the IAC

Weird....

Strange that the IAC fixed it last time you had the issue and not this time. Is this the one that was running hot at idle?

My memory is foggy and I can't remember if the drive lube switch opens or closes to sounds the alarm, I'm guessing closes.. You can always unplug the drive lube sensor and take a spin.

If you need anything let me know, I can make some calls.

Frank

No that was the other motor and I did both impellers and thats fixed.They sure are a lot easier to get to when the manifolds are off.It runs great just the alarm but no codes I had it scanned.Do you think it could be because there are two baffles in that motors exhaust?I doubt it but it is odd I don't even think the 6.2s have a water pressure switch.The other motor is a little louder now that its thru hull only.

I could be wrong but I can't see the exhaust being the cause unless the new hose routing is somehow effecting the cooling system sensors.

It's kinda hard to tell what it is. I'd have to check around with some of my buddies who are still in the business..I'm not current on some of this.

The new exhaust is run exactly as original used the same hoses just had to extend two.The other motor is fine.

The IAC is the most common failure but there may be an issue with crank sensor. On occasion the crank sensor plug in connector will get corroded from even slight circ pump leaks. The sensor is located at the 7 o clock position jsut behind the balancer. Corroded pins will not show up on the scan tool as it is triggering a signal, just not a strong one. They are pretty easy to change out. I would take them both out, check the connectors, clean them then swap them port for stbd. See if the problems moves to the other motor or goes away completely. i have on occasion bought brand new IAC's from merc that were faulty and expensive. NAPA has the IAC's and the crank sensors. They come off of a 2003 Lincoln Mark IV. The IAC cost is $28.00 and the crank sensor is $19.00

The 6.2's do have a water pressure switch. It is located in the top of the power steering cooler at the rear of the motor. I had one of these go so bad that the motor wouldn't start. The scan tool didn't pick up a fault either because it was stuck reading 39 LBS water pressure. NAPA and Advance Auto carry these as well but I would only buy them as a quick weekend fix. These have a steel housing not brass.