Topic: Suddenly No spark, but have power at coils, electronic ignition culprit?

[vorhese]

I went to start up my 750 this morning, and it started right up and then stopped.  No spark. I have a fully charged battery. I'm getting full voltage at the coil and at the electronic ignition power connection.  I've disconnected every connection and put them back in. Neither coil is firing.  The only thing i can think of at this point is something happened to the elec ign, but it'd be odd for both to go out suddenly and not getting spark from either.  I have under 2 hours to figure this out... any ideas?

[flybox1]

any chance the ground wires from the ignition have been damaged? Some electronic ignitions use a verity small gauge signal wire and they are susceptible to being pinched or broken.

+1
and along those lines, the other day i had cylinders drop out, and one of the small male black/white wires from the coils had come out of its female attachment.
must have caught it on the underside of the tank.  its all i could think of.

[vorhese]

I've got a simplified wiring right now, a simple power wire from the battery with a inline fuse, straight to the elec ign and coils. That wire is hot.  The blue and yellow wires from the elec ign back to coils seem fine.  But I don't know how to test them.  I have a multimeter but my ohms only go down to 200, and even then, I'm not sure what to test for. One coil or one elec ign pickup may possibly go bad, but not two at the same time... so bizarre.  I'm on the verge of slicing open the power wires down by the pickup and see if I'm getting power down there.    How do I test the signal coming back from the elec ign at the blue and yellow wires?

EDIT: I put my multimeter on ohms 200  and connect the elec ign red to blue for one test, and red to yellow for the other.  Each briefly reads something like 40, 180, and then stays on 1. 

Is there a way to test the yellow and blue wires from the elec ign when cranking the bike? It should be sending some sort of signal to the coils right? I just don't quite understand what to test for.

And is there a way to trick the coils to spark with the elec ign?

[vorhese]

I used this test to test the coil

I plugged the multimeter in to the primary side (black and blue wires and black and yellow wires) and got 4.5 ohms. I changed the meter to 20K and I plugged one into one primary wire and one into the plug and got no reading. I tried both primary wires, both coils, nothing. I tried it on my other running cb750 and got the same results.

[vorhese]

Ok I plugged both plugs per coil together and got 14,500-15,000. I think the coils are good.

[mystic_1]

as I understand it (disclaimer: I am not 100% on this) the Blue/Yellow wires are "ground" wires. This allows the coil to send a spark when the "signal" gets it ground.

Close.  The blue/yellow wires ARE ground wires, but the spark happens when the ground is DISCONNECTED.


When the blue or yellow wires is grounded, this allows power to flow through the primary part of the appropriate coil, energizing it.  When the ground is disconnected, the magnetic field inside the coil collapses and the plugs fire.

You should be able to bypass the ignition module and test them the coils/plugs as follows:

Remove both of the spark plug which connect to the coil you're testing, and stick them back into the plug wires, then ground both of them to the engine case.  Now disconnect the blue or yellow coil wire as appropriate per the coil you're testing.  Turn on the key and the kill switch.  Ground the coil wire for a moment, then observe the spark plugs as you disconnect the coil wire.  You should see a spark.  If you do, the problem is in your ignition module.

mystic_1

[flybox1]

I used this .pdf extensively when testing my charging system, before enlisting the help of the forum.
gather the test info, then report back...
http://www.hondachopper.com/garage/troubleshooting_charging_system/troubleshooting_charging_system.pdf

excerpt from hondachopper.com....
Testing coils
The coils on these bikes are very easy to test. There are two sides to the coil. The primary and the secondary. The primary
side is the small connectors that attach to the wiring harness. The secondary side is the spark plug wire connectors. We
are going to test resistance, so the coil must be isolated and de-energized. Basically, disconnect the wires from it. You do
not want it attached to the wiring harness for testing.
PRIMARY RESISTANCE
Set the multimeter to measure ohms. Use one test lead on each of the small terminals that attach to the wiring harness. If
using stock coils, you should get a reading of approx 5 ohms. If using DOHC or most aftermarket "hot" coils the reading
should be about 3 ohms. If your readings are very far off from the given values, the coil is probably bad. If you do not get
a reading, or if it flickers in and out, then there is a broken wire and the coil is bad.
SECONDARY RESISTANCE
Set the multimeter to measure ohms. Once again we are going to isolate and de-energize the coil. Use one test lead in
each of the spark plug wire connectors. You may have to wiggle them around to get them to a spot where you are getting
a reading. Depending on the coil you should get a reading of 5Kohms to 20Kohms. I don't have a manual with me so I will
edit later for the actual cb750 specs. If you get no reading, the coil is bad. This test can also be performed with the plug
wires and caps in place. Due to the extra resistance though you should get a reading between 10Kohm to 50Kohms
depending on the coil, wires and caps. If this is done first, and there is no reading, do the test without the wires. If you get
a reading with no wires and no reading without, then the wires are most likely your problem.
INSULATION BREAKDOWN
These coils have a solid metal core running through them. It is used solely for mounting. It is not a ground. Sometimes the
insulation inside the coils starts to break down and the coil will short to the metal core. Set the meter to measure ohms, or
use the continuity function if your meter has one. You can use resistance(ohms) because even if it has no resistance it will
read 0 ohms. This shows that there is continuity. Continuity means that electricity can pass. A wire has continuity, but if
you cut it in the middle, it does not.
What we are going to do is use one test lead on the center mounting bar. The other test lead is going to go to each of the
primary terminals, and each o the secondary terminals. In effect we are doing 4 tests. If any one shows continuity to the
center core, then the coil is bad.
One other thing to remember is that the coils do get hot with use. It is possible for a coil to test good, but once it gets hot,
the insulation inside starts to get gooey and breakdown. If it starts to misfire after it is hot, let it warm up until it happens
and check the coil while it is hot. This can be tricky because it still needs to be disconnected first.

[vorhese]

So I tried the hold to ground and let go to fire the coils. Worked like a charm.  I cut a little bit of wire away at the elect ign to check for hot wire, and I do have one.  I think the thing is done, not sure how old it is.  I put in an old set of points and it's firing like a champ.

[scottly]

I've got a simplified wiring right now, a simple power wire from the battery with a inline fuse, straight to the elec ign and coils. That wire is hot.  The blue and yellow wires from the elec ign back to coils seem fine. 

No ignition switch or kill switch? If power was applied continuously, it may have over-heated the ignition. Just what electronic ignition do you have?