Have a friend that has a 2008 boat with a standard 496 engine. They were running down the lake about 3000-3500 rpm when he backed out of the throttle the engine died. He took boat to mechanic and they replaced the IAC but said IAC went bad and caused the ECM to burn out. Mechanic said next week he is going to try another ECM to see if it will not throw that code again.

I can see where this is possible but have never heard of the ECM going bad when an IAC goes bad. Has anyone else heard of this?

Has happened tons of times with the 496's. Whipple and some others can sometimes fix the ECU.

IAC, pigtail to the IAC, and ECU can all be harmed. Be careful ! Don't want to burn out another ECU.

Do a search as there are tons of threads on this.

Edit in: some are putting separate fuse in the pigtail harness to keep it from knocking out ECU in the future.

Also the IAC 'muffler' getting very dirty. The muffler is a small air filter for where the IAC sources outside air.

Okay, jus type in IAC to the search box and 75%+ of the threads that will come up are for 496's. Make sure you read a bunch of them....especially those that mention the wiring pigtail and ECU. Oh, and we have figured out which Ford part # it is also.

Thanks for quick response. Will do some reading.

I edited above to include the IAC 'muffler' also.

DO NOT put another ECM on there without installing a known good/new IAC...
...AND checking the pigtail for melt/burn/compromise.

Else, you will have two blown ECMs. My local buddy who only get's on OSO occasionally has a 496 Mag ECM that had the same damage, and he had Whipple fix it.
I'm not sure if he'll sell it or not. If you want me to find out, let me know.

If I recall correctly a new ECM / PCM is a bit more money thru whipple than a merc dealer like myself. If buying a new one buy it thru your local Merc dealer. Also not all ecm 's are repairable. Some even have more than one internal problem as well. Also I have been here and there repairing a few ECM's and PCM's along with testing them.

You also can ohm test the complete IAC circuit, connector and the IAC itself to see if problem(s) still exist.

First and foremost send your PCM to whomever to get tested making sure its bad. to begin with. There is more than one player whom can do this.

How did the shop determine your PCM was bad ? Scan of the engine showing bad PCM fault code - correct ??

Also the Merc ecm 555 for 4.3 and 5.7 and 6.2 use the exact same IAC as the 496 and has ruined those ECM 555's thru out as well - its not just the Merc 496 only that can have this issue for a failed IAC driver and or even more issue than that.

Volvo Penta rarely has this problem of failing ECM / PCM 's from sensor(s) like Merc does just saying.

If you find out you need a PCM for a 496HO. I have a good one no longer needed.