no spark on #2 cylinder

[naughtyG]

So after fixing all my electrics the old '86 ran fine... for a few days.

Then it started missing, and then feeling like it was running on 3 pots, only going to full power when in higher revs. I thought it might be the #2 coil, as I had noticed a break in the insulation of one of its wires.

I replaced the #2 coil with one from my 2000, no go. I replaced the HT lead as well, still no go. Tried the #2 spark plug in another cylinder and it fires fine. All three other spark plugs give a good spark, but nothing on #2.

Any ideas? :ummm:

 

[tugla]

coil wires broken in the connector or not making good connection.....maybe

 

[dannymax]

Could be corrosion in the plug cap G, there's 3 or 4 contact points in them that can give problems. unscrew the brass fitting that grabs the sparkplug tip and the resistor, small brass disc and spring will fall out.

If you don't have COP's, that is.

 

[naughtyG]

Is there some kind of test I can do on the harness side of the #2 coil wiring? What should I see on there? Voltage pulses? Resistance?

To me it points at the TCI unit..

 

[Rusty McNeil]

Not really answering your specific question but one test to do to eliminate carb or synch issue versus spark issues;

Use a clamp on inductive timing light on the high tension wire and see if its firing that way. Your not timing anything just seeing if the coil is firing.

Many times I've used this to discover that what I thought was a firing issue was actually an inadequate fuel supply at idle due to clogged pilot fuel jet, clogged idle circuit, poor synch (Throttle plate closed to far at idle) or improperly adjusted a/f screw or whatnot.

Another clue is if the bike seems like it suddenly "wakes up" and is firing on all cylinders again as you roll into the throttle. If it does this it probably is a fuel issue.

 

[Rusty McNeil]

Could be corrosion in the plug cap G, there's 3 or 4 contact points in them that can give problems. unscrew the brass fitting that grabs the sparkplug tip and the resistor, small brass disc and spring will fall out.

If you don't have COP's, that is.

+1,
Very common problem

 

[Rusty McNeil]

I've also had what looked like perfectly good plugs that wouldn't fire, replacing them fixed it. Although you stemmed to have eliminated this possibility.

The plugs ( At least the NGK standard part number) ought to read about 4000 ohms or so between tip and body. When I've had problems with the plugs in this regard the reading was extremely hard to get without digging deep and hard through the surface with the meter probe, or impossible to get a reading at all.

 

[wildweasel_pt]

The wire from the TCI to the coil connector may be broken or the connector prongs are corroded or oxidized (TCI connector and coil connector)? If the plug is sparking when removed then you have no problem with Coil or HT lead. When you start it and let it idle for a while then remove the plug if its wet then your idle circuit is working.

 

[dannymax]

Not really answering your specific question but one test to do to eliminate carb or synch issue versus spark issues;

Use a clamp on inductive timing light on the high tension wire and see if its firing that way. Your not timing anything just seeing if the coil is firing.

Many times I've used this to discover that what I thought was a firing issue was actually an inadequate fuel supply at idle due to clogged pilot fuel jet, clogged idle circuit, poor synch (Throttle plate closed to far at idle) or improperly adjusted a/f screw or whatnot.

Another clue is if the bike seems like it suddenly "wakes up" and is firing on all cylinders again as you roll into the throttle. If it does this it probably is a fuel issue.

Hell of an idea, never been a big fan of grounding a plug....

 

[Rusty McNeil]

I don't know about our TCI or the Dyna's specifically but in general "some" ignition modules can be damaged when operated without a load.
Whenever I used to do the spark check by removing the plug I always made sure to get a good ground clip on the loose spark plug so it had a definite path to ground, rather than just trying to hold the thing up against the engine or something...

 

[naughtyG]

I definitely have the syndrome of 'waking up' suddenly at higher revs which could point at a fueling issue, but I have tried holding the spark plug to ground while hitting the starter and I get no spark on #2. Plenty of spark on other three plugs.

I've replaced the coil - no spark
I've replaced the HT lead - no spark
I've tried another plug - no spark

I'm going to try a continuity check on that coil wire and hope that is it.

Is there no way to check if the pulse from the TCI is coming through ok?

 

[alorio1]

Youre TCI couold be bad, each coil has it's own diode which supplies the coil with voltage. I could be badly mistaken so don't let me take you into deep waters, but here is the info I have on TCI's and this is a C&P from some other site;

I do not have a schematic for the DCI PCB but it appears to have 4 independent
channels, one for each coil/sparkplug channel. There is one of these diodes in
each channel. In addition to those diodes, there is on the PCB edge next to the
heat sink row. This diode had what appeared to be heavy deposits of oxidation.
When I attempted to de-solder the diodes, all but one fell apart.

--The Fix:
Since this is the low voltage flash circuit for the coils, I picked up a couple
packs of 3 amp/400 PIV diodes from Radio Shack as replacements (RS #
276-1144/P/N 1N5404). There is plenty of room on the PCB for them but I did have
to clean out the lead holes real well. The PCB is also double sided so you must
ensure the complete connection is made to both side. I flowed the solder on both
sides just to be sure. After the new diodes were installed, I applied a
conformal coating to the areas affected by the work. This way if the new
components worked I would not have to de-solder the terminal connection again to
remove the PCB to access the component side.

After reinstalling the PCB into the housing/case, I plugged it up to the
connectors on the bike and rechecked the supply voltage, it was now at full
battery supply voltage. I cycled the main key switch several times to see if the
plugs would still spark when the switch was taken to the Off position, they did
not spark. I reattached all the spark plugs to the installed plugs and tried to
start the bike and it started right up! I blipped the throttle a couple times
and all seemed to be good, but shut it off at that point until I get everything
back together for a ride. I will give a follow-up report after I get a ride or
two in. I have since resealed the DCI cover with a Hi-Temp silicone and
reinstalled it. I am in the process of reinstalled everything else I
disassembled during the troubleshooting process.

 

[naughtyG]

Thanks Alorio.

From this I deduct that with the key on, one of the wires (red/white I assume) should have +12V, and the other coloured wire is the grounding one to produce the spark?

 

[johnpclynch]

+12v on the Red/White, ground on the other (this ground is disrupted to collapse the magnetic field and induce your high voltage spark)

I had the same symptoms as you, and this is what was wrong with mine

 

[naughtyG]

I'm gonna investigate some more, I hope mine's as easy as that!

 

[bazwell]

Um, check if you have 12v on one side of the coil. Then, run a wire from earth and then just act like a human set of points, touching and releasing the earth wire to the coil. You should get big fat sparks.