496 quit on power reduction
 

all running great. Pulled back for no wake zone. Engine quits, no start, scan shows IAC High output, cam sensor ,cranksensor map high input... Any ideas. Looks. Like pmc burp....

Before we get rolling with this I WILL NEED your year model of the engine and the engine serial number and is your app completely stock from OEM Mercruiser ? If not stock details please. Without this info its a dart throwing contest.

Need to know if you have a tach signal when cranking the engine over ???

2004 stock 496 ho wil get serial tomorrow and check tach signal, Had weird crackling noise in engine bay, could not pin point it. Almost sounded like leaves burning, no smoke no smell..

I would check the IAC connector / connection and IAC wiring and the IAC itself for extreme overheat and or melted and for shorts. I would check all fuse portions and relays engine related and look for any melted portions and or shorts.

Your engine still cranks over is this correct ??? ---- If so look for TACH signal as well. Also while cranking I would check to make sure ignition spark is not jumping across / arching somewhere externally. ( your words crackling noise) = my guess without eyes or ears or hands on it.

Make sure ignition wires are not jumping spark especially number 7 and make sure all spark plug boots are connected and again NONE are jumping spark or split or worn thru and that applies for all spark plug wires. This possible could be one of your problems along with a IAC related problem.

ALSO CHECK THE FUSE FOR THE IAC CIRCUIT

Also check cranking voltage and does the battery cables become hot while and or after cranking. Make sure you have the safety stuff on board like a working fire ext and no gas fumes.

I still want the engine serial number because there is always the CAM and Crank Sensor to deal with. The CAM sensor is an issue all within itself depending on engine serial number.

Have you tried giving it a little throttle when starting it? If the IAC is down you may not be getting enough air to keep the engine running. Also, cam, crank, and map sensor share the same 5 volt reference power. Make sure you have a solid 5 volts on the gray wire. While your in there you might as well check the ground integrity as well, the ground wires are typically black with a tracer color on it.

Will check all. Did have an AIC connector fry on me when first started up after installing all new plugs and wires. Replaced and ran a trip or two since no issues. AIC was my first suspect but found no heat or melting....

Serial OWO40139, tach drops from 500 to 0 on start or crank, checked wires and pmc platform. Found AIC disconnected, do not remember leaving off while limping home but might have with the crackling noise. Reconnected and engine fired up. Will try another run when the tides comes up... Maybe AIC overheat? I put new mufflers in the throttle bodies.......

You have to clean and make sure the IAC cavity and long hose connected is NOT RESTRICTED especially from a old IAC muffler that could has got sucked into and or the freakin BELT DUST so all of that needs to be 100% clean and free. THESE are IAC killers and cause very HIGH IAC duty cycles and still set IAC codes along with poor running conditions, and or hard engine starts to engine stalling especially on de-acceleration .

Man my first words in my POST # 4 - " I would check the IAC connector / connection ". Sometimes you get lucky and sometimes you guess right and sometimes you are just that good. I like to think all 3. lol

The reason for the CAM & CRANK fault codes was because the engine stalled on its own while seeing RPM. FYI

wow i have been reading horror stories about the IAC and the iac muffler. i think i will be buying a spare to have on hand at all times.

at least half are owner self inflicted ^^^^^ You can search what is up here for what can cause IAC failures - I know I listed a bunch as well. If you take care of all engine related items they can last. I have some 10 plus years still running the same IAC. Not hard to do at all. Easiest first step is cleaning your flame arrestor 100 % perfectly all the time inside and out. Next is to clean 100 % the throttle body and throttle plate and of course the IAC cavity, IAC hose and of course a new IAC muffler once a year min for starters - this alone can double the life. There is more