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Hi, looking for some help. I have an overspeed alarm showing on my smartcraft gauge. Here's what happens:
  1. If I put the hammer down, the overspeed alarm will go off when I near 4000 RPM
  2. If I gently get her on plane, the alarm will not sound until around 4000 RPM
  3. I can push through the 4000 RPM barrier at times
  4. It does seem to be somewhat trim sensitive. If I trim it all the way down, it will trigger the alarm (though it never did this when I bought it.) If I trim it up just right, sometimes it doesn't trigger the alarm. But sometimes it does. I'm really at a loss here.

Some other facts - First, I have scoured the internet for weeks. I know some people like to point to websites that might have the answer. I probably already read it. I am really hoping a mechanic savvy person reads this and can help.

- The boat started doing this last year. It is a 2004 engine. I have owned the boat since around 2012/13 and it never had this issue.

- All routine maintenance has been done. I still need to change inline oil filter (called for at 300 hours)

- I recently change the Thermostat and Poppet. T-stat was stuck open and changed poppet because I had it apart. Temps are now in line with service manual specs.

- Water pressure seems on spec according to manual also - at idle and on the way to 4000 RPM. I did not get to wide open throttle.

- I read in the Mercury Guardian page that it could be due to prop, engine height, or engine trim. While it is trim sensitive, I didn't have this problem until a year ago. Nothing has changed there. I want to make this right because this will be my last year with this boat and I want it running perfect when I sell.

- I also read that you shouldn't rev the engine in neutral. I did that before I knew better. That is the only thing I can figure. It had something to do with a shift switch. Computer telling the motor it's over revving because it thinks it is in neutral instead of Forward.

Any help would be appreciated. Motor is real clean and has 346 total hours.

Thanks in advance.
 

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thats a real interesting deal there, i had a motor act like that ( 40 ) hp once, it sounded like the clutch slipping when ya gassed it , the rpm s would go way up and i would have to back down to get prop to keep grabbing. turned out the prop hub was spun and slipping, replaced and all good..
 

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Bobby, have you verified the operating RPM with a second device ? If the Indicated RPM is consistent with your Smartcraft guage & say a timing light w/ tach then possibly the ECM is throwing an errant code. The latter is just a guess on my part but I'd definitely want to make sure the reading on my Smartcraft guage was correct. Your dealer could verify this as well with a laptop. Mike
 
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