Unreliable spark Tohatsu MFS6C

[Matunucktuna]

Tohatsu MFS6C (2012) has been unreliable. Have run it half throttle, under load, for 45 minutes at a time with no problem. Shut it off, and restarts…wait for over an hour and restarts. Come back to the boat the next day and it either starts right up, or may refuse to start no matter what is done…not even a splutter. I leave frustrated, come back the next day and it starts on first pull.
Yesterday, when it would not start, I checked for spark (holding plug against ground bolt) and no spark. Disconnected kill switch wire…no spark. It is sounding like the igniter, but I have never heard of one acting like this. At $144 plus shipping, I would like to verify that the igniter is the culprit…any ideas? Thanks…

 

[pvanv]

The issue with intermittent electrical items is that you can't measure the failure unless they are failing at that moment. I have never seen a failed ignitor, but anything is possible. Make sure the insulation of the brown kill wire is not damaged.

 

[Matunucktuna]

The issue with intermittent electrical items is that you can't measure the failure unless they are failing at that moment. I have never seen a failed ignitor, but anything is possible. Make sure the insulation of the brown kill wire is not damaged.

Thank you for the response. This version of the igniter only has two quick disconnect terminals and the sparkplug wire. To be sure, I removed both the kill switch wire and the wire feeding the oil pressure light…still no spark.

The issue with intermittent electrical items is that you can't measure the failure unless they are failing at that moment. I have never seen a failed ignitor, but anything is possible. Make sure the insulation of the brown kill wire is not damaged.

Thank you for your quick response!
This version of the igniter only has two quick disconnect terminals, and the spark plug wire. To be sure, I disconnected both the kill switch wire, and the wire feeding the oil pressure light. I also checked the gap to the laminations. Still no spark.

 

[MattFL]

Does the shop manual give a method for testing the ignitor?

 

[Matunucktuna]

Thank you.
I actually just downloaded the service manual for this engine, and it does include a table of resistance values for the igniter connections. I will check the readings tomorrow and post the results.

 

[Matunucktuna]

I measured resistance values of the igniter and compared them to the table in the service manual. The measurements in range were between the plug wire and ground, and also the “resistance cap” measurement.
Any of the measurements involving the stop terminal or led terminal (oil pressure), were extremely high.
Hopefully the table is correct…(although I did notice a major typo).
I will order a replacement and when it arrives, I’ll measure and compare the readings.

 

[km1125]

Did you actually replace the spark plug? I've definitely had cracked insulators before that had intermittent issues. From the first post it appears you used the spark plug to test for spark, but if it was cracked internally you would not have seen a spark at the tip.

 

[Matunucktuna]

Thanks!
Yes, I did replace the plug early on; sorry I should have mentioned that fact in my post.

 

[Matunucktuna]

I finally received the new igniter, and measured the various resistance values. The readings of the new igniter are similar to the original igniter: neither are a complete match to the table in the service manual. (I tried both an analog multimeter and a digital multimeter). Obviously, I was hoping to see the new igniter’s resistance values a complete match to the table values.
The good news is that the motor seems to be working now with the new igniter, but time will tell. If it does continue to work reliably, I will assume the original igniter was intermittent for some reason.