Mercruiser Ignition Troubleshooting

[CorpusTahoe]

I have a 2006 Q6 Tahoe with a MCM 4.3L TKS engine, alpha 1 drive and a thunderbolt IV ignition system. Several weeks ago my boat would turn over but would not start. I followed the Mercruiser troubleshooting guide where I checked for a spark using a spark plug tester. I have no issue getting a spark when grounding out the green wire from the ignition module, but when I try and start the boat I don't get a spark until after I stop trying to start the engine. IE I get several sparks prior to the engine coming to a complete stop, but not while the starter is engaged. The Mercruiser troubleshooting guide recommended replacing the ignition sensor which I replaced along with the distributor and rotor and am still having the same issues. I also noticed the ignition coil is arcing from the purple wire to the center of the ignition coil when trying to start the engine. I checked the resistance on the primary and secondary and they were within typical ranges and wiped it down to ensure it was clean.

Would appreciate any ideas you might have to track down the issue.

 

[achris]

... I also noticed the ignition coil is arcing from the purple wire to the center of the ignition coil when trying to start the engine. ....

Replace the coil. Even cleaned, you won't get rid of the carbon track now there, and it'll keep arcing. Also check your battery voltage at the coil+ while cranking. Shouldn't go below about 11 volts. If it does, recharge or replace the battery. And make sure it's at least an N70Z.

 

[Scott Danforth]

Agreed, you have one of the few true coil issues

 

[CorpusTahoe]

Thanks for the quick reply. I added some dielectric grease to the terminal as a quick check and the boat started right up. Will order a new ignition coal to avoid having to rely on the dielectric grease. I also replaced both my batteries during the troubleshooting process as they had each lost a few cells.