How do I tell if it's a power pack issue or higher up?

I have a 1978 9.9hp Johnson that was recently gone through and was running fantastically. I took it out last weekend and it got me out to the fishing spot, but wouldn't start to get me home. Luckily I wasn't too far and had a full trolling motor battery.

In diagnosing it, I noticed both plugs were failing to spark. Both sparks going out at the same time make me think it's something higher up. Wouldn't be likely both plugs went out at the same time and also wouldn't be likely both ignition coils quit at once, right? I did hook up an inline spark tester and couldn't get an indication of current.

So that leaves it either the Power Pack or the Sensor or Coil on the flywheel, right? Are there other things that could be wrong and how do I go about narrowing it down further from there? Do Power Packs quit all at once?
My friend is a lawn mower guy and said it sounds like a bad pick-up coil, but I am unsure how that translates into outboard motors and which part that correlates to.

Any help would be greatly appreciated! Motor model is 10R78M

Force OB motor power packs were notorious for quitting all at once, but even worse ... would work the next day, but then not the next.

Is there any 'ignition kill' circuit n that motor? I'd check that 1st. On motors 25hp and less and I've owned dozens, I've never lost a powerpack. FWIW, you can buy a PDF of the original OMC Factory OEM Johnson Service Manual for $10-$20 and Jim has a page listing some in the Motors forum. That has the test for the Stop circuit (but bypased), where if it passes but has no spark at both plug gaps, then go to the Charge Coil Test.

See attached, if it helps, for another article from online:
View attachment Maintaining Johnson 6hp & 8hp Outboards, 1992 – 2005.pdf

Thank you, most people describing a bad power pack online mention it running "rough" rather than not at all like mine is. Now that I re-read some of them, I'm guessing that they are describing boats with multiple power packs and more than 2 cylinders so that some cylinders keep firing and running the motor. That tidbit about Force motors quitting all at once is helpful!

I did check the kill switch to ensure it didn't get mashed in the kill/short position and found it working as expected. Got continuity to the ground when depressed and continuity stopped when released so it left me confident it wasn't stuck on and bypassing the plugs.

I've been using Leeroy's Ramblings and he describes if everything else has been tested, then try the power pack. Is there a simple way to test the flywheel coil or sensor to ensure it's not higher up before trying a new power pack? Any chance it's the stator?

If anyone stumbles upon this thread, I'd highly recommend you give Leeroy's Ramblings a read for older Johnson 9.9 and 15hp motors. https://www.leeroysramblings.com/Johnson%209.9_15.htm

Again ... OEM Service Manual is worth its weight in gold! This is the data from a similar vintage 8hp JohnnyRude:

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Thank you again, DaleH. Complicated instructions (for me) but thorough and a great explanation of how to test things. I guess I had better learn how to use my multimeter beyond continuity testing.

Frankenfish said:

Thank you again, DaleH. Complicated instructions (for me) but thorough and a great explanation of how to test things. I guess I had better learn how to use my multimeter beyond continuity testing.

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I lost all spark all the sudden on my 20hp and it ended up just being the Power pack ground not making a clean connection.Mostllikely it had never been off before. Took connection loose and cleaned it up a little even though it looked good and spark returned.No problem since.

Went through the steps DaleH provided, wasn't getting bupkis from the sensor. Decided to pop the flywheel off and take a look at it and the darn thing was smashed to bits! Also there wasn't a flywheel key!?!? I've ordered a new key and sensor - but WHERE DID THE KEY GO? Do those things spontaneously disappear?

I've attached two pictures of the sensor damage/carnage.

DaleH, thank you for the troubleshooting guide. Wasn't expecting the damage to be so obvious, but the steps pointed me right to it.

Well...... there’s your problem right there. :shock:

Who went through this motor and how big a hammer were they swinging?

O U C H !

DaleH said:

O U C H !

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The thot plickens. Looking for the missing flywheel key, I found it hugging the flywheel magnet. There's obvious dings and scratches on the inside of the flywheel where this key chattered around. I suspect this is what did the smash job on the sensor coil.

Will this damage on the inside of the flywheel cause any issues? Do I need to grind off the burrs now present on the edges of the flywheel magnets?






Something I'm really confused about - does my motor have a [strike]magneto[/strike] stator? The parts diagram shows a [strike]magneto[/strike] stator but I can't find one at all on the motor. Do only the electric start motors have the [strike]magneto[/strike] stator?

Update - Got the new sensor on and the flywheel re-seated with a new key. The motor fires right up! I even had enough confidence in the repairs that I took the mother-in-law out in the boat!

Did end up stranded and relied on the trolling motor to get the last 200 yards to the boat ramp. Already have that problem fixed, it was a bad fuel line fitting causing it to suck more air than fuel down at the gas tank. Figured something was up when the primer bulb felt "slushy" with air. Life goes on and I have a forgiving mother-in-law.

Thanks again for all the help folks!

Glad you got it fixed ... and that your last minute stranding didn't turn your Mother-in-Law into an 'outlaw' :shock: !