Rear Cylinder: NO SPARK - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 71 (permalink) Old 05-09-2008, 12:24 AM Thread Starter
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Rear Cylinder: NO SPARK

On my 1992 VN750, the rear cylinder doesn't fire. Confirmed this in two ways. First I started the bike and pulled the spark plug wires off of the rear spark plugs (one at a time) no change to engine harmonics. I then Pulled the wires off of the front plugs with a notable change to engine performance and sound.

I shut the bike off and hooked up my spark plug tester to the the rear cylinder plugs. Re started the bike. No Spark. I checked the coil IAW the Clymer Manuel. the Primary Resistance was Exactly 2.2 ohms. The secondary resistance was just about in the middle of the range, so I knew that measurement was good.

I swapped the front coil for the rear coil... rear fired front didn't...so i know that the Ignitor works properly, so i was wondering is 2.2 to 2.3 ohms to high? and is it possible for the spark plug boots to loose continuity? I am not getting continuity through the boots. But i don't think this is the problem, because I checked all 4 boots with the same result.
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post #2 of 71 (permalink) Old 05-09-2008, 01:11 PM
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so u switched the coils and the opposite cylinder fired? that would mean the coil

1990 Kawasaki Vulcan 750

.... slightly modified
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post #3 of 71 (permalink) Old 05-09-2008, 11:52 PM Thread Starter
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That's what I thought too..but when i put a new coil on....it started all over again. That is why i was asking is .1 to .2 Ohms that far off that would make the coil not fire?
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post #4 of 71 (permalink) Old 05-10-2008, 08:42 PM Thread Starter
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Ok got another question in this same subject. When i got the bike, the PO also gave me a big box of parts that he had gotten at the local Japanese Bike Scrap Yard. In this box are 4 Coils. I called him up and asked him about them and he said he had no clue to as if they were good or not. So I was wondering is there any other kind of bench test for these other than the Ohms test? Is there a machine like AutoZone uses to check car Ignition Coils? Just wondering before I start trying one by one on the bike, because all 4 of them read .1-.2 Ohms over the max what the manual says is good.
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post #5 of 71 (permalink) Old 05-10-2008, 09:05 PM
 
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Ohms is a reference not a solid figure, you can have great ohm readings and have a dead coil; Run a test light to the primary, is it flikering? If so, then your coil is getting the energy pulse, if its not, then you have to trace back.
Let us know.
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post #6 of 71 (permalink) Old 05-11-2008, 12:41 AM Thread Starter
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Ok Now i feel like an idiot...and I hate seaming this way. Now on cars, there is a positive (+) and negative (-) primary wire. do motorcycles have both? Reason being, I don't know which wire is my Primary Wire, i know the secondaries are the spark plug wires. and I know that the secondaries aren't working... I also understand the theory of putting the test light in...the testlight would work much the same way as a NOID Light on a car's Fuel Injection System. Steady on would mean that there is constant power (which i can't think of a good reason why), a flashing light indicates that the system is running normal, and no light means that either the pickup coil or the ignitor box is bad.

So with that said, we know that that the pickup coils are good, because one cylinder does in fact fire?
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post #7 of 71 (permalink) Old 05-11-2008, 01:18 AM Thread Starter
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Ok hooked up the test light trial and error way. one wire flashes and the other wire does nothing...tried the spark plug tester again..still Nada. Now then I figure green wire = negative (it was the wire that didn't flash) and the other wire would be the positive (it flashed). Now with this new information in my wise years of mechanical knowledge and my youthful years of exploding batteries I have learned that hooking ground to hot and hot to ground causes problems (they don't call me "Sparky" for nothing). So I would think if it was a big deal the coils would be labled + and - on the primary wires like on the old Ford Ignition Coils. But mine are not, so am I safe to assume that the wire placement doesn't matter...or did i fry my new coil?
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post #8 of 71 (permalink) Old 05-11-2008, 09:31 AM
 
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You are correct slim, one will be a solid ground whilst the other is your pulse.
Some cars have a solid positive and the coil driver pulses on the ground side;
So the red wire pulses! That sounds correct according to my wiring schematic. I dont think you can cross them incorrecty if they are not marked.

Ok ; So now the other wire should be a solid ground; Probe that wire and then probe the negative side of the battery and see if there is continuty;
What i have done in the past, is to make my own ground with a peice of wire, you will be bypassing the ignitior on the ground side, whilst the ignitor pulses on the positive; Give that ago, you maybe loosing the ground through the ignitor.

You did mention that if you change the coils around then it will fire. so that means that you had the other coil disconnected or,did you have them both plugged in? Try putting the bad coil on the front cylinder.
The ignitor may not like having both coils hooked up, meaning an internal fault in the ignitor;

This spark tester that your using, is that a generic one or does this have the bulb in it;
Resistance test your spark plug wires also, How are the plugs?
Just throwing out ideas, i am sure you have tested all that, but i have not read the whole story.

I have to run to the shop, but ill keep an eye out for your reply.

Last edited by Mastertech; 05-11-2008 at 09:57 AM.
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post #9 of 71 (permalink) Old 05-11-2008, 10:43 AM Thread Starter
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Yes i checked resistance of wires. They checked out fine. I am not so sure as the spark plug boots because my Ohm tester leads aren't long enough to go all the way down inside the spark plug end. I am going to try to back probe the spark lug side of the boot and check again.

My spark plug tester is a home made tester I made out of a spark plug and some 12 gauge wire soldered onto the threads of the spark plug, I have an alligator clip soldered onto the other end of the wire. I get good continuity between the spark plug and all ground points. The tester works on the front cylinder but not on the rear, so I am quite sure that the tester works.

Plugs are brand new. I replaced them before trying anything else...The old ones looked perfect when i pulled them out. light tan colored, no black, burnt or destroyed electrodes.

I am going to do that continuity check from green to battery ground. I will post more in a few minutes after I run these new tests.

https://www.vn750.com/forum/images/smilies/doh.gif Why didn't I think of grounding out the coil my self. I usually think to do simple things like that. KISS (Keep It Simple Stupid) has always been my motto, but here lately every thing i touch I read to deep into it... Thank you for reminding me to get back to basics.
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post #10 of 71 (permalink) Old 05-11-2008, 10:50 AM
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Quote:
Originally Posted by slimvulcanrider View Post
Yes i checked resistance of wires. They checked out fine. I am not so sure as the spark plug boots because my Ohm tester leads aren't long enough to go all the way down inside the spark plug end. I am going to try to back probe the spark lug side of the boot and check again.
Stick a known good plug in the cap and test at the electrode. a non resister type plug would be best

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