85 43 no spark

"The boat will run great until

"The boat will run great until it decides to shut down. Then i will have no spark, the tach will bounce right before it quits few minutes later it will start back up run for a bit then do it again? cap rotor all look good, any ideas?"

My bet is a dying coil. Could

My bet is a dying coil. Could be the tach is contributing. Disconnect the tach and see if it dies next time out. If it does then get a new coil.

Thank you Guy. I will try that

Thank you Guy. I will try that. On the coil does it have to be a marine rated?

"Sealed coils are the same for

"Sealed coils are the same for marine or wheeled vehicles; either oil or epoxy filled (except for maybe brass studs, washers and nuts). The epoxy filled is for high vibration protection.

Merc PN: 392-805570A2 COIL, IGNITION (oil filled)

I put a BLASTER epoxy filled coil on my 4.3L recently; put the 10 yr. old coil in the tool box as a spare.

If by chance (I doubt it) your engine has points let us know; may need a different coil."

"Thanks again, there are no po

"Thanks again, there are no points. what are the chances that the thunderbolt IV is going bad?"

"You'll have to test it im

"You'll have to test it immediately when it dies. If the coil doesn't fix it, the optic trigger sensor under the rotor could be going out if it's covered in rust and corrosion. Check it w/a digital ohm meter before you run it w/all wires removed for a base reference. Test it asap wires removed when it dies.

Tests for Thunderbolt Ignition:
W/ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!

#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

#2 - If 12 volts is present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

#3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

#4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced."

"THANKS AGAIN, I apperciate th

"THANKS AGAIN, I apperciate the info I will give it a shot and see what happens."