help with 496 mercruiser

[bugum]

I just bought a boat that came with a 2005 496 mercruiser and bravo outdrive, the prblem i am having is that as long as i keep the rpms at 1500, she runs great, but the minute i go over that the motor knocks and pings and looses power. But then if I shut it off and restart it, it will run good but only at 1500 rpm. If I start the motor and immediately get up on plane it runs good for about 30 seconds then looses power and shuts down. any suggestions?

 

[Don S]

Re: help with 496 mercruiser

Assuming you have done the basic preventive maintenance items like tuneup, and fuel filters. It's time to get it hooked up to a diagnostic tool and find out what is happening. Did you have an alarm of any kind?

 

[Philster]

Re: help with 496 mercruiser

They only real diagnostic without doing what Don suggests is noting the oil pressure. What pressure is she running at when things go bad?

 

[tpenfield]

Re: help with 496 mercruiser

I just bought a boat that came with a 2005 496 mercruiser and bravo outdrive, the prblem i am having is that as long as i keep the rpms at 1500, she runs great, but the minute i go over that the motor knocks and pings and looses power. But then if I shut it off and restart it, it will run good but only at 1500 rpm. If I start the motor and immediately get up on plane it runs good for about 30 seconds then looses power and shuts down. any suggestions?

Did it do this on the sea trail before you bought the boat?

I'm thinking fuel and timing, are the things to check out.

 

[burp]

Re: help with 496 mercruiser

The 496MAG engine has a bunch of sensors which can create problems. Too many to guess which one is the culprit and throw parts at.

Follow Don's advice, he is usually spot on with his advice and diagnosis.

 

[CharlieB]

Re: help with 496 mercruiser

With absolutely NO RETURN on electrical parts, you will soon learn that following Don's advise will save you a lot of money, time, and greatly lower your frustration level.

 

[bugum]

Re: help with 496 mercruiser

Assuming you have done the basic preventive maintenance items like tuneup, and fuel filters. It's time to get it hooked up to a diagnostic tool and find out what is happening. Did you have an alarm of any kind?

I took your advice and ran a scan it had about 13 codes so I addressed the lower numbered ones.
I replaced the manifold heat sensor which took my code count to 4. The scan still shows a code on sea water temp and
Pitot code. Hopefully these items won't affect the performance . We shall see by Friday when she goes for a run.

 

[Buzzards Bay]

Re: help with 496 mercruiser

How did you make out with your diagnostic repairs?
I am doing a sea trial on a potential purchase of a boat with a 496 Mag HO next week. Anything I should be paying particular attention to besides holding tightly to my hat?