88 4.3 mercruiser wont start

the engine will crank but no spark at coil. i have replaced coil, cap, rotor, Ignition module inside distributor and CD ignition module on exhaust manifold. no change in anything. the boat doesn't a cut off switch for the driver. Any help will be great. I am thinking it could be the shift interrupter but i dont know of a way to test it or where that is located.

Look at the shift bracket where the control cable and short cable meet. There is a micro switch with a roller on the end if the arm. The roller sits in the middle of a V notch.
If it is not and the switch is engaged then that shorts the ignition to ground. this is call the shift interruptor switch.
It gets made when shifting out of gear and kills the ignition for a split second to allow gear and clutch dog to seperate.
If this switch is bad and is in the closed condition allowing it to short the ignition all the time this will cause a loss if 12 volts to coil.
Also look at your key switch and make sure you have 12 volts on the purple wire when the key is in the on position.
The12 volts toignition starts at the key switch and goes back to motor.
Also giggle the main wire harness connector. The large black one at the motor.

Check these and report back.

LakeMonkey said:

the engine will crank but no spark at coil. i have replaced coil, cap, rotor, Ignition module inside distributor and CD ignition module on exhaust manifold. no change in anything. the boat doesn't a cut off switch for the driver. Any help will be great. I am thinking it could be the shift interrupter but i dont know of a way to test it or where that is located.

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I have checked the Shift Interrupter Switch and it is in the proper place with the roller in the notch. I also read online that I could test the Shift Interrupter by disconnection a single wire from it and then should allow motor to start. This didn't change anything, there is still no spark at the distributor. I will need to check the key switch wire when I return to the boat. I have un plugged and re plugged every wire harness I can find. Thank you for your help. Side note: Prior to this issue my daughter and I were out in the boat running very smooth and lots of good power for around 40 min. Then a sudden loss of power for about 5 min then boat died and has not restarted since. I appreciate any advice

Ayuh,.... Is there Power at the coil's (+) terminal, with the key "On",..??

Yes. There is power at the coil Positive terminal with the key on