Could PU coils ohm good and still be bad?

[wayne z]

OK, still no spark from the rear coils. I have exhausted all my capabilities. Have tried 3 different ignition boxes and all 3 (the original and a loaner and a bought used one from a runner) still don't correct the problem.

I have cleaned all the connectors and continuity tested all involved circuits of the rear ignition coils and PU coils. Also changed the ignition coils and wires.

There is 12+ volt reading at both, supply and control wires to the ignition coils with power on and engine not started. Idling on the front cyls, the control wires of the rear coils show pulsed readings instead of steady 12 volts. I don't know if this is normal or not, seems to tell me the coils are getting a signal? Still no spark at the test sparkplugs.

Only part not changed yet is the PU colis. I have a loaner from Sean, a purchased one from a good runner and the original installed one. They all ohm the same, at 116 ohms to all pins using the black wire as neutral.

Could the PU coils test good with the meter and still not work correctly?
I'm ready change it out and see.

Thanks,
Wayne

 

[Fire-medic]

That is a yes. They may go open (infinity-no reading) once they get hot.

 

[scuff]

yep I had it happen to me on my Dodge pick-up, never on a motorcycle, but very frustrating never the less...

 

[D-Max2012]

Happened to my 91, two summers ago..

 

[Fire-medic]

It has happened to me twice w/my VMax in 22 years of ownership.

 

[wayne z]

OK, I think I found the problem. I bit the bullet today and pulled the seemingly good testing PU coils.
Look what I found stuck to the rear coil. This could surely affect the coil's magnetic signal.
It was prolly laying in there somewhere out of the way and found this location when the bike fell off the stand twice while I was fighting the fire.

 

[D-Max2012]

Hope that resolves your issues..

 

[Fire-medic]

Geex, I don't think there's that much of an air gap between the rotor and the pick up coil. Anyway, let's see what happens now.

 

[wayne z]

Geex, I don't think there's that much of an air gap between the rotor and the pick up coil. Anyway, let's see what happens now.

The driver bit was stuck to the back of the coil, 90 degrees from the air gap.

 

[wayne z]

OK, back to the drawing board. I changed the pickup coils and still no fire at rear coils. Every electrical part on this bike has been swapped except the Vboost controller and servo. I tried unpluging it and also tried unplugging the tach, for they both get signals from the gray wire to the coils and ignition box, just in case they were faulty and corrupting the ICU signal.

Guess I will go back and inspect very closely all the circuits, pins and connectors involved.
Anyone have any other ideas?

 

[D-Max2012]

you've already changed the ECU. you've already changed rear spark coils.. you get no spark on the rear cylinders, but you're seeing this "No Spark" on a test spark plug.
"thinking out loud here"
That doesn't make sense, if the two in the front are firing.
So, if the wires going to #2 and #4 are swapped somehow to #3 and #1, the timing would be totally off.
Also, I'd take the actual plug out of #1 and #3 to look for spark directly. Check for fuel on these two while you're in there.. It would be messed up if you had a double whammy going on here. A busted test plug and no fuel on the rear carbs. Just food for thought.

 

[wayne z]

Thanks but those thoughts already crossed my mind and I tried 2 new test plugs at the same time. Also picked them up and held closely to ground while engine running in case plugs were internaly shorted, not even the smallest arc can be seen.

I am going to look more carefully at the connectors and wiring.

 

[D-Max2012]

I am going to look more carefully at the connectors and wiring.

Yes.. I agree..
My 91 was neglected when I got her. While trying to resolve my own PU unit failing after she warmed up, I found many connectors that needed attention. So I took the time to unplug (one at a time), each connector I could reach, and inspect the connectors. Most were good, so those only got a shot of dielectric grease. There were some that needed a micro filing to remove corrosion and a re-crimp of the blade connector, along with grease.

 

[wayne z]

OK I FOUND it!

Thinking about it some more, I realized that the only thing left that needed more scruitiny was the red/white wire that supplies power to both rear coils.

So i checked continunity again and got shaky readings when I wiggled the harness above the #3 area.

I used a stickpin and multimeter and started probing the wire.
Shure enough, I found the wire was corroded in two inside the insulation about an inch foreward of a factory splice.

I cut 3 inches foreward of the splice and 3 again and still was getting lot of green powder when stripping. I tried a jumper there and it RUNS on 4 now!.

Tomorrow I will keep clipping and stripping until I get fresh looking wire, solder and shrink tube the splices.

It's been a learning experience for sure. I now completly understand the Vmax wiring.

 

[D-Max2012]

GREAT!!.. Glad to hear you nailed that biotch. :eusa_dance:

 

[Fire-medic]

Yes, I've had a dissolved wire inside the insulation close to the factory crimped terminal. When I started doing the same thing, looking for a break in continuity, I was able to feel the powdered copper wire where the stranded wire had deteriorated. I did the same thing, stripped it back to good, shiny copper wire, and no green corrosion, soldered up a short splice and a new connector, and that was it.

Now you can enjoy your bike.

 

[alorio1]

Good trouble shooting Wayne.....Now I know where to bring my bike with electrical issues.

 

[scuff]

always nice to hear the conclusion of a problem that's what makes this forum so great, weather's getting nice let's go RIDE !!!!!!!

 

[wayne z]

OK, I took her for a couple test rides today, with a fire extinguisher LOL.

Runs fine but still have a little electrical glitch. Seems the oil light and neutral light are crossed somewhere.

Now, the oil and neutral light come on with key on and oil light goes out when shifted out of neutral. Runs awesome though!
Gimmie a day or so, I'll figure it out, I love the challenge of hard problem LOL.

 

[one2dmax]

That is about the only pair of wires you can mix up and the colors are not coordinated where they plug in (under the left side panel).