Help with ignition diagnosis

I've lost ignition on #3 cylinder.
I cleaned, gapped and swapped plugs...#3 still doesn't fire.
Spark shows at #3 plug
Swapped #2 & #3 plug wires...#2 doesn't fire, #3 fires.
Ohmed coils...21.1Kohm through NKG(5kohm)plug boots on secondary.
Did not check primary side.


Ok,
I want to bounce my diagnosis off yoozguyz to make sure that I am not missing something stupidly simple or some XJ quirk that I am not aware of.
According to the Yamaha factory service manual, if I am seeing things correctly, the most likely problem would be insulation breakdown in my #3 plug wire. If the pick up coils were bad the issue would be with both coils or both wires from one coil. Not one cylinder...
Same goes for the TCI, if it were the problem I would be having issues with 2 or all cylinders, not just one.
If the primary or secondary side of the ign. coil were the problem I would loose both cylinders...
Occam's Razor says bad plug wire? I haven't had an opportunity to check for arcing in the dark yet.

So, waddaya think? Am I even close or am I blowing smoke up an exit orifice?

 

If you've got spark on 2 but not 3 it's either the plug, the cap, the wire or internal to the coil.

You might try swapping the caps. The internal resistor can fail.

 

The plug caps are brand new but I will try swapping them. Not to mention that the coil, wires and caps ohm out correctly at just over 20K.

If the coil(secondary or primary) were bad, wouldn't it effect both cylinders?

 

what leads you to believe it's a ignition problem?

 

Swapped the plug wires and the problem followed the wire.

What else could it be ? If it was a compression problem or carb/fuel issue it remain in the #3 cylinder and not follow the #3 plug wire...
Or am I missing something?(seriously, I know I can miss the forest for the trees!)

 

FWIW

I have no problem with the labor involved with cutting into the coils and replacing the wires. I just don't want to do it and then find out the issue was the ign. coil itself or the pick up circuit... By the same token I don't want spend more than I have to but will install the Dyna coils if necessary.

 

try taking the the plug that doesn't fire now and swap it with 1 or 4 plug

 

Already did that. The plug works fine in #4.
I still have to try swapping the caps but I have to wait for the sun to get a bit higher.(the neighbors are funny that way!)

 

Luv, I've done post-mortem on a few coils and have found that in 3 out of 4 cases (the breadth of my experience) the high tension leads were faulty. The coils themselves were fine (with the afore mentioned single failure). I'll suggest that you cut back the #3 line about 5-6mm and reset the cap. If that doesn't buy you happiness, I'd look into replacing the high tension lines. It is possible, there is a write up in our DIY links section.

 

Polock,
Just swapped #3 and #4 plug caps. #3 cylinder still doesn't fire. Then I verified that the problem follows the plug wire (swapped #3 wire with #4 cap to #2 cylinder and #2 wire to #3 cylinder) the problem does follow the wire.

Robert,
I just replaced the plug caps a month ago (thanks Chacal!) and cut the leads back 3/8" then. I'll try it again.It certainly can't hurt!


No dice! Damn!

Forgot to submit this before I ran out to trim the lead!

 

i've got 2 spare coils and 3 bikes and it's a nice day for a ride
just say where and when

 

PM sent!

 

We've covered (and argued about) this before.

These are wasted spark systems that fire their two plugs in SERIES. As such, the only ways you could be firing one plug and not the other on a single coil are:

1. The non-firing plug is (relatively) shorted somehow, like a bridged gap. Sounds like you've already eliminated this possibility here by swapping plugs around.

2. There is some other false path shorting out the non-firing side of the coil. This is a tricky one because of the way these wires are set up. In your case, it's particularly weird because you're seeing pretty normal resistance (maybe just a bit low) from cap to cap. Still, if your observations are correct, it sounds like the #3 side of your coil is arcing to ground either from the wire (which should be relatively obvious) or inside the coil body. If it's from the wire you should be able to move the wire away from the chassis and get intermittant spark on #3; in that case, coil surgery would be a solution. If it's inside the coil body, and new coil will be needed.

 

Yes, something that test just fine with a multimeter can easily be shorted out at 5K volts.

Pull the tank and run it in the dark. Leaking wires are easy to see in the dark.

 

OK!

Polock to the rescue!

Swapped out the coil and problem solved. She's up and running again.

Thanks Tim and sorry about Bob!

 

something tells me you ain't seen the last of Bob
i believe he was serious about buying my bike right there

 

There's a reason why I don't have much to do with my neighbors!