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BF 9.9 Dies soon after starting

I'm think I will try both suggestions starting with checking continuity of wiring from sensor to cdi plug, and if that checks out then do a coolant line flush light,
 
I would like to know if the sensor is a Positive Temperature Coefficient (PTC) type sensor. That means that the material it's made from increases in resistance as it gets hot.
At room temperature it would have very low resistance between the wire terminal stud and the threads on the sensor body.

Conversely, if it's a Negative Tempeeature Coefficient (NTC) type, the material it's made from decreases in resistance as it heats up. It should have high resistance between the body threads and the terminal stud at room temperature.
 
I think the sensor is probably an NTC that loses resistance as it heats up and provides a ground to "turn on" the engine protection feature causing the power reduction and engine stall. Disconnecting the wire takes ground away and disables engine protection.

But...I think it's possible that wire could be very slightly touching ground someplace where the insulation is chafed or damaged and is causing the engine protection to be activated.
Just a theory though.
 
jgmo said:
I think the sensor is probably an NTC that loses resistance as it heats up and provides a ground to "turn on" the engine protection feature causing the power reduction and engine stall. Disconnecting the wire takes ground away and disables engine protection.

But...I think it's possible that wire could be very slightly touching ground someplace where the insulation is chafed or damaged and is causing the engine protection to be activated.
Just a theory though.
Click to expand...
I just measured the original sensor ; at room temperature = 2.5k ohm after heating up sensor with heat gun reading is .4k ohm so yes resistance drops as sensor heats up
 
Because of the symptoms you're seeing, you might want to look carefully at that wire for any sign of it possibly finding unwanted ground someplace.

It's sort of a "hack job" approach but, just to get my outboard working so I can use it, I would be tempted to snip that wire near the CDI plug and the sensor and splice in a replacement. If it works, I might just leave it that way or choose to dig the original out of the harness and tidy it up during off season.

If a new wire doesn't cure the issue then there's the possibilty of something being wrong with the CDI.

HOWEVER...
...making sure the oil pressure portion of the Engine Protection system isn't causing the problem would be wise before making that call.
 
And , since it appears that your heating the original temp sensor may indicate that there's nothing wrong with it, there's still the possibility that there could be some sort of overheat condition taking place like the "localized hot spot" I mentioned previously. Possibly caused by mineral deposits. Your plan to try flushing could help with that.

As to flushing, NSDON has written about how effective his use of vinegar mixed in water has been. You might want to read those posts
 
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