NO Spark from one coil 75 hp Force

[seahorse1317]

I have a 1997 75 hp Force with ignition problems on bottom cyl. It started missing last time I went run it, always ran great before. I tested for fire with my spark tester, top two fire steady, last one sparks once or twice a second. I swapped the coils and the problem stays on the bottom. I ran out of daylight to start tracing the wires. I am a auto tech and want to learn the electrical system on this engine. Any one have a wiring diagram for it ? Ser. # OE 264486 If you need to email it send to gsoileau1317@yahoo.com thanks for any help... Greg

 

[seahorse1317]

Re: NO Spark from one coil 75 hp Force

Forgot to ask, What is the most common item that will cause one coil not to fire? thanks Greg

 

[pnwboat]

Re: NO Spark from one coil 75 hp Force

A lot of things can cause your symptoms.

1. If you have the Mercury Thunderbolt ignition system that uses the modular Coil/CD packs, the first thing to check is the "bullet" connectors between the CDM and the stator and the trigger assy. Make sure your ground wire between the CDM mounting plate and the engine block is making good contact. Also make sure the ground wires (Black) from each of the coil/CD pack (they're all tied together) modular connectors are making good contact under the bolt that attaches them to the mounting plate. Make sure one of the pins in the modular plug for #3 Coil/CD is not bent or pushed back.

2. Make sure all six of your flywheel magnets (they're under the flywheel) are intact and not broken or missing.

3. Check your stator resistance (black stators have a higher failure rate that the red ones) between the White/Green and Green/White wires. It should be between 500 - 700 OHMs.

4. With the engine running, you should read 3 volts AC between each of the trigger output wires (Purple, White, Brown) and ground. You can't actually measure the resistance on the trigger assy. itself like on the older Force Prestolite triggers because it uses a "Hall Effect" solid state circuit.