lost cylinders 1/4 while on the interstate

[CincinnatiKid]

A bit of a head scratcher.... was riding home on the interstate this afternoon and the bike suddenly lost power. I have a pretty sensitive digital tachometer installed, wired to read from the right side coil. The tach read 0 from the moment the power loss happened. I was able to tap the headers while riding and found 1/4 were not nearly as hot as 2/3. Limped it home on 2/3, thankfully.

Background: New Dyna coils installed a month ago, proven with a 600 mi road trip.

This evening, i made some tests, here are some facts of what i found:
- I have full battery voltage at both coils
- I have robust continuity from the igniter to the coil negative leads, both sides
- I have continuity from each pickup wire, at the pickup itself, to the input into the igniter
- Both pickups exhibit magnetism.
- The seal behind the advance mechanism is a little leaky. but the pickups and the advance mechanism were both oil-free.

the digital tach, reading 0, tells me that the problem is upstream of the coils, no pulses reaching the coils. that leaves the igniter or the pickups.

Any tips or tests to further isolate this issue? in a different thread here, i saw that there is an ohm spec for the pickups. i didn't see it inside my haynes manual. if somebody can share that, that might help.

time to start shopping for parts....

[CincinnatiKid]

$150 for dyna S pickup system.

seems like the move, but it would be cool to definitively find the culprit at play here.w

[salty_monk]

Wire from pickup rubbed through? Ignitor gone bad?

[bobgroger]

Tach shorting out?

[CincinnatiKid]

Tach shorting out?

worth looking into...
I’ll remove it from the circuit and see if I can’t get power back.

[gs11ezrydr]

Remove tach assembly. Remove spark plugs,Reverse the primary wires from #1 #4 coil and reinstall on #2 #3 see if it kills them.If so trace all the wires if ok probably need a new Dyna S assembly..Possibly...Seen them fail in the past.Some last like forever and some don't.

[CincinnatiKid]

Found the issue, though it means my testing gave me a false positive.

at bobgorger’s advice, I made a check on the tach wiring, which was attached to the 1/4 coil negative post.
tach checked out, no problems. Removed it from the circuit and bike still didn’t fire on 1/4.
Went to reinstall the tach wiring and found that the wire from the igniter to the 1/4 coil had broken @ the ring terminal @ the coil. copper broke between the wire insulation and the ring crimp. Bummer. Put a new ring terminal on it, and it’s back to good.

curious as to why I would have seen/heard continuity from the igniter harness plug to the coil terminal when I measured it 2 nights ago, but I guess it’s water under the bridge now.


This begs another question though... the Dyna S module (contact breaker assembly and igniter box replacement) should arrive at my door in a few days. Keep it and install it, or return it?

thank you again to bobgorger for the tip to investigate the tach terminal.

[bobgroger]

Keep it. I have them on all my bikes, and the former location of the Ignitor is a great place to install a SH775 Regulator.