Do a comp check...Sounds like a rocker nut backed off or a broken push rod...That will kill the power and you would be running on 7 cyls. That would not throw any codes either. (it might be and easy fix. Pull the valve cover and fix it)

When a Fault Code is set there should be a soft alarm (two beeps per minute) and there will also be a reduction in Available Power (Rev Limit) to 90%.

With a hard alarm (constant beep) there can be an additional reduction in Available Power, and depending on the fault, it could go as low as 0% (engine shutdown).

You said that the WOT RPM dropped to 4400, which is exactly where 90% Available Power would put you. However, you should get an alarm and your performance at idle would not be affected. But don't get me wrong, I completely agree with the guys above who say that a scan is the best place to start.

I think you would have heard it if you had a rocker nut back off or broke a pushrod, but you could have dropped a cylinder for some reason, either mechanical, ignition or fuel.

Not a CKP, you would have a no start condition if the CKP was toast. It sounds like a non-critical sensor has "failed in range" meaning you will have no alarm, but possibly have a sticky code set which has limited your RPM range and does not sound an alarm. Could be a CTS, or an ETS, but definetly not a CKP.

If you want a scanner for yourself get one from:

http://www.rinda.com/marine/marine.htm

Get the Mercruiser Scan Tool, and you can scan your motor, and all your buddies motors too, as well as reset your IAC's, and perform a variety of other diagnostic and maintenance issues.

i had that happen to me a few years ago. i got back to the dock and opened the hatch. i was so pissed off and everyone knew it and they just kept making it worse. everyone had something to say. im checking everything and making sure everything was right and i remember this guy just standing there telling me" your not going to find the problem like that" then bam!! there was the plug wire. plugged her back in closed the hatch and told the guy to have a nice day. i love easy fix stupid things.

Being in Owasso, I would say take it up to Morton Marine. They are mostly a bass boat dealer, but also sell runabouts with the merc 496 and HO engines. They are a certified mercruiser service center. I had them winterize my boat in 2006, and they also helped out with getting my boat on its new trailer in 07. They have always treated me right and are good guys. If your engine is stock merc, take it by and have them run a scan.

If it isn't stock merc, I'm not sure who I'd send you to. My engine builder, Brad Smith, is in Joplin, and does a huge amount of high end marine engines. If you want to go that far, give him a shout.

The alarm could be broken.

I think you would have heard it if you had a rocker nut back off or broke a pushrod, but you could have dropped a cylinder for some reason, either mechanical, ignition or fuel.[/QUOTE]


I had a rocker nut back off completely and there isn't a sound except a very slight rough idle. Only loss of rpm down about 300 -400. Motor "carried" very well as a friend put it. Would even plane and run very fast on 7 cylinders.

I'm not at all saying from a distance that this is your problem. I am saying however, that it could be the problem and your description matches my past symptoms.

Good luck & borrow a scan tool

Yes I went to them and they said that there was not enough facility to work on a 30 ft boat. I was sure hoping they would take a look at it. I am going to see if they can pull the codes if not I am going to contact Ugly Johns and have a "interview" with them and how I expect my boat to be fixed.

Sunday I will pull the valve covers off and see what I can see, I just hope the gaskets are reusable. I am also going to pull the plugs and ohm the wires also and also check the fuel pressure statically sitting in the shop with the motor running.

check the spark plugs have seen these go bad for no reason motor will still idle and run pretty well:)