need help, why did my 496 blow at 4400rpm?

harley · Sep 29, 2004

Has this happened to anyone else? I have a 2004 Sonic 31ss with T-496 HO's. We were running the lake at about 70mph, 4400 RPM. when the starboard motor made some pretty bad noises and stopped instantly. The motors have 68 hours on them, the oil has been checked every time out and changed at 50 hrs. We usually run the boat around the 50mph zone with an occasional run faster. The smartcraft read out on the motor say "cam and crank sensor faults" which to me sounds like a timing chain. This is the first time we have ever ran the boat for any length of time at that RPM.

The good news is... We are still on warranty and it is the end of the boating season here. Now I must weigh my options, do I replace the 496 and be done with it or do I trade the motors in for 500's or 525's. HELP

CAUSIN TROUBLE AGAIN · Sep 29, 2004

common problem for the 8.1

cam and crank sensors are a problem all the time in the truck 8.1 G.M master tech told me....easy check take the sensor out of your good motor and try it in your problem engine not hard to do.. 15 min time

cfm · Sep 29, 2004

That's too bad. If it was meant to happen I guess it was a good time for it to happen - in Warranty - end of season, etc/etc.

I would discuss options with the Dealer since There are things they are subject to do as part of the warranty agreement.

Wally · Sep 29, 2004

Re: common problem for the 8.1

CAUSIN TROUBLE AGAIN said:
cam and crank sensors are a problem all the time in the truck 8.1 G.M master tech told me....easy check take the sensor out of your good motor and try it in your problem engine not hard to do.. 15 min time

I've heard that too! Landscape owner i know keeps a spare in each of his trucks for field repairs!!!

Rock Steady · Sep 29, 2004

Sorry about the mishap.... but heiii yeah get the 525's if you can... would be awesome...

Reckless32 · Sep 30, 2004

Yep have your sensors checked especially the crank. Big problem on earlier 496HO models. Had two new (at the time) boats experience this problem locally back in early 2002. Motor goes into safe mode and basically shuts down. The older motors also had recalled push rods. I'd run a check with Mercruiser to see if that S/N engine had been done for that as well. Other wise your motor will detonate if that's not already the problem.

need help, why did my 496 blow at 4400rpm?

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