Running about 3000rpm when engine alarm sounds for about ½ second despite no signs of anything wrong. Fifteen minutes later, engine shuts down completely and without warning. No sputter, no surge, no nothing. Just shuts down.

Two hours later when attempting to refire, I get one short blast of the alarm when turning the key to on position. Engine then cranks but won’t fire. Symptoms of bad crank position sensor are similar except engine refires after about 15 minutes only to die again. That’s not the case here.

Any opinions are welcome.

ttt

You da man Bobby but not many opinions here are there.

Yeah i guess so. I wish i could help you. It was good seeing you down at tiki yesterday.

There was a problem with the 496when it was first introduced. Simptoms are very near what you are descibing. I dont know the details but someone here will.
A buddy had the 496 in his 3/4 ton Suburban and sold the truck after 4 months because it was unable to be located after going to the dealer more than a dozen times. He couldnt get the lemon law because they blamed it on the 4 TV's he had installed.

Maybe one of the 700 sensors is grounded.

I had one do that, Motor would turn over but not start, came out to be the trim sensor on the drive that shorted out, thats tied into the PCM, I was told that you can unplug it, and it will on the circuit, Single plug located behind Eng, with tag Indicating trim. 2002 496 HO.................that was my........1 out of a 100

My brother just bought a boat with a single engine 496Mag HO. He had a similar problem. His dealer replaced a "bad sensor" and it seems to be operating fine now. To my understanding the bad sensor was detecting a overheating problem and shutting off fuel to the motor. The problem was the engine wasn't overheating.

John,
It was good seeing you again at the Tiki Bar. My friend has a 496 HO in his Sunsation 288. Had the same problem except the motor never shut down completely. It went into the Safe Guard mode.It would not turn over 2500 rpm. Turn the key off and back on it would start right back up as if nothing was wrong. Then it would give that one short blast when he turned the key on. The first time the oil pressure sensor was showing he had 100 lbs of oil pressure. They replaced that sensor and it was fine for a season. This last time it was a bit more complicated because the scan tool didnt show any code but it was doing the same thing. They replaced the crank sensor, didnt fix the problem. Finally found a sensor unpluged some were that monitors water pressure. He had the impeller replaced, not sure were the sensor location is that measures that,(sorry) and the sensor was never pluged back in, pushed it in and its been fine. Have you done any work on your boat lately? The mech. that found the water pressure sensor unpluged says he always goes over every ground wire making sure they are tight also.

Randy

Will it run over 3000rpm? If not it may be the neutral rev limit. It thinks you are in neutral. Just a thought.