johnson 90 blown power packs

[baltra]

After rebuilding my 1985 johnson 90, it has blown partially 2 power packs, only one cylinder on each side gets a spark. After replacing the first pack, it worked fine for a little while, but then it failed. Before rebuilding the engine, the two old power packs worked just fine for the longest time, never had a spark problem, even after running with the batteries in short circuit and burning my radio, gps, fish finder and all other electronic onboard, all cylinders always got full spark, but now, I can't keep the engine running good! Any suggestions on what to check (and how to) that can be blowing the packs?
Thanks!!

 

[Fleetwin]

Re: johnson 90 blown power packs

Those engines don't like poor electrical connections. Especially the negative battery cable to engine block connection. Remove it, clean it and reinstall.

 

[Joe Reeves]

Re: johnson 90 blown power packs

Any suggestions on what to check (and how to) that can be blowing the packs?

Voltage To Powerpack Failures
(Magneto Capacitance Discharge Systems)
(J. Reeves)

The usual cause of having those type powerpacks fail repeatedly is having a very small of voltage applied to the Black/Yellow wire (Kill Circuit) at the pack. Test as follows.

Disconnect the Black/Yellow wire at the powerpack.

Insert either a ampere meter or a volt meter set to its lowest DC voltage reading between that Black Yellow wire and ground.

With the ignition key in the OFF position, observe the meter reading. Now turn the ignition key to the ON position and again observe the meter reading.

Any reading, movement of the meter needle, would indicate that battery voltage is being applied to that Black/Yellow wire. If a reading is present, remove the other end of that Black/Yellow from the raised terminal of the ignition switch.

If the reading ceases to exist when the Black/Yellow wire is removed from the ignition switch, replace the switch. If the reading continues to exist, there would be a short of some kind in either the engine or instrument wiring harness.... to determine which, simply unplug the large RED electrical plug at the engine which would eliminate the instrument cable.

Note that the black/yellow wire must not have any other wire attached to it for the following reason!

Keep in mind that any accessory that has 12 volts running to it, especially when turned on, will have voltage flowing thru it and trailering out thru its black ground wire to complete the circuit. If that accessory has it's black ground wire attached to the "M" terminal that the black/yellow wire is attached to.... you will have voltage flowing directly to the powerpack.