Johnson V4 90, missing spark

[Jungleboat]

Hi,

Was crusing home and the engine misfired a bit, then ran as normal. Did this a couple of times then slowed to a crawl.

Hard to tell in bright sunlight but the top left cylinder doesn't seem to have a spark?

I tried changing the plug, no difference.

If the weather is any good tomorrow I'll go back to the boat and check for anything obvious but in the meantime:

What's the most likely cause?

How much does a "powerpack" cost for this engine - and what the heck is it? Is that the same as a distributor or something?


The engine is quite ancient, early 80s apparently.






JB

 

[bktheking]

Re: Johnson V4 90, missing spark

There are 2 powerpacks on each side of that motor right off the head (if it is indeed an early 80's 90 hp) . When one powerpack dies you will loose spark but not total spark. I lost spark on one bank once, I retightened the ground to the powerpack and it came back and has been back ever since. Not hard to tell at all, one head will be cold and one will be hot, the one that is cold is dead. Do a spark check with a tester just to be sure. Check the plugs and wiring going to the powerpack as well. Swap powerpacks and see if dead spark follows the powerpack, easiest way to check.


Here is some troubleshooting info:

http://www.cdielectronics.com/downl...1978-1998 65-140 HP (Without Quick-Start).pdf

 

[Jungleboat]

Re: Johnson V4 90, missing spark

That's very helpful, thanks!

All 4 plugs were hot when I took them out but that's because it had just been running and I was checking on the river.

I'll pop up to the mooring today and try checking the ground wires.

One other thing - we ran into a muddy sandbank 10 minutes before, managed to keep it moving and turned around back into deep water. I checked the inlet holes were clear and that it was still throwing water out the back.

I don't think it was over-heating, as it re-started and continued home very steadily at low power for about an hour. But could that episode have caused anything?


JB

PS Yes, I need a fishfinder with depth gauge!

 

[emdsapmgr]

Re: Johnson V4 90, missing spark

The pack is the likely culprit. In addition to swapping the power packs, you can swap the two coils on that side. If anything changes, that will tell you what to replace. If you get no change, you should check the output of the timer base and the stator. Since all these components are expensive, some investigation/testing first will save you $ in the long run.