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Help needed: Harley no-spark situation

  1. #1
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    Help needed: Harley no-spark situation


    Been working on bikes for a long time, but this is probably only the 2nd or 3rd Harley I've worked on, and none of them remotely this new.

    Bought it recently and it wasn't getting spark. Seems like the PO was throwing parts at it trying to fix it, but did not succeed. Here are some of the critical details. If anyone has any pointers as to what I can check next, it would be greatly appreciated. I have a manual, but it's so generic that it's not very helpful.

    1991 FLHTC
    - New battery (~13.5V consistently)
    - New coil
    - New plugs
    - Have tried a used ignition module and pickup trigger out of a known good running bike ('93 Wide Glide)
    - Cranks over good
    - Only gets ~5V at the coil
    - Has approx. 4.4 Ohms at the coil
    - With 12V directly to the coil, it will produce a spark
    - Kill switch, starter relay and all circuit breakers seem good (checking breakers by checking resistance...not sure if there is a better way)
    - The voltage gauge on the dash only ever shows 10-11V
    - At some point during the diagnosis, my radio mysteriously fried (smoke coming out of it, now powers up, but doesn't make a sound)
    - I was comparing the two ignition modules. The one that came with the bike is #32405-91 (correct), and the alternate one that I was trying out of the '93 is #32405-91A. 91 signifies the year it was first used, so the 91A is likely a revision of the original one with some minor differences (just guessing). However, when checking the resistance at each connection and comparing the two, they were TOTALLY different. In my mind, that means they are either completely different by design, or the original one is junk. Either way, neither of them have lead to me getting spark.
    - Most of the wiring seems to be in really good shape (i.e. not hacked to shit)

    I think the root of my problem is that I'm not getting enough voltage to the coil, correct? The next thing I was going to try is disconnecting the stator. I'm hoping to see that it has a short in it, and it is sucking voltage away from the coil. I'm not even sure if that is possible though. Am I naive to assume all of my grounds are good since everything else on the bike is working normally (pretty much, anyway)?

    Any help is greatly appreciated!

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  2. #2
    Lifer
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    Re: Help needed: Harley no-spark situation

    You're getting 13.5V at the battery when running, but only 10-11V on the dash and 5V at the coil inputs? Do you have wiring diagrams? I'd be curious if the dash measured voltage from some common point with the coils. Bad ground, short circuit, or high resistance connectors all seem possible.

    What about unplugging the fried radio, in case that is the source of a short, hence the smoke?

    Full disclosure, my electronic diagnostic is relatively amateur compared to at least a few others here.

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  3. #3
    Member ducatirdr's Avatar
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    Re: Help needed: Harley no-spark situation

    Typically its a weak source to ground (-). I would check the ground to the frame for both the battery and the coil. Check are ground cables, there should be a bare woven wire grounding strap from the inner primary area to the frame. That rusts out and can be nothing but a big resistor on these rubber mounted engines.

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  4. #4
    Lifer jasnmar's Avatar
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    Re: Help needed: Harley no-spark situation

    I'd look for ground problems as well. They can cause all sorts of weird behaviors.

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  5. #5
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    Re: Help needed: Harley no-spark situation

    Thanks guys. I'll start digging for ground issues. Theoretically, could I ID that there is a grounding issue by using a heavy jumper (like a jumper cable) from the negative on the battery to the frame and/or motor? Then if there was a bad ground I would get spark, and then I could find/replace the bad ground?

    Quote Originally Posted by aldend123 View Post
    You're getting 13.5V at the battery when running, but only 10-11V on the dash and 5V at the coil inputs? Do you have wiring diagrams? I'd be curious if the dash measured voltage from some common point with the coils. Bad ground, short circuit, or high resistance connectors all seem possible.

    What about unplugging the fried radio, in case that is the source of a short, hence the smoke?

    Full disclosure, my electronic diagnostic is relatively amateur compared to at least a few others here.
    I don't have 10-11V on the dash when running, because it's never been running. That's just sitting with the key on. I haven't put too much weight on that issue because (in my experience with cars) those usually show how the battery is charging. So if it's not running, it's not charging. So I wouldn't expect an accurate reading. I could definitely be wrong here though.

    I pulled the fuse to the radio just to eliminate it as a potential issue. The radio wiring is a clusterfuck, but I actually think it's an OEM clusterfuck.

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    Last edited by nick5446; 01-30-17 at 04:02 PM.

  6. #6
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    Re: Help needed: Harley no-spark situation

    Here are some pictures for you curious cats
    Attached Thumbnails Attached Thumbnails Help needed: Harley no-spark situation-img_7912-jpg   Help needed: Harley no-spark situation-img_7913-jpg   Help needed: Harley no-spark situation-img_7927-jpg   Help needed: Harley no-spark situation-img_7928-jpg  

    Help needed: Harley no-spark situation-img_7938-jpg  

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  7. #7
    Lifer
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    Re: Help needed: Harley no-spark situation

    Quote Originally Posted by nick5446 View Post
    I don't have 10-11V on the dash when running, because it's never been running. That's just sitting with the key on. I haven't put too much weight on that issue because (in my experience with cars) those usually show how the battery is charging. So if it's not running, it's not charging. So I wouldn't expect an accurate reading. I could definitely be wrong here though.
    Excuse me while I hang my head in shame. Seeing 13.5 I assumed that was running output. You know, besides the whole 'no spark' thing.
    I wouldn't read that much in to the dash being 10-11v then either. Maybe a little low, but tough to say if it's related. In theory, it should show roughly what the terminal posts show when your ignition is on, with the draw from the radio, lights etc. Usually reads a bit low due to voltage drop. Does seem like a big delta.
    Quote Originally Posted by nick5446 View Post
    Theoretically, could I ID that there is a grounding issue by using a heavy jumper (like a jumper cable) from the negative on the battery to the frame and/or motor? Then if there was a bad ground I would get spark, and then I could find/replace the bad ground?
    Wouldn't that identify a short circuit, a positive wire shorting/grounding to the frame? When you contact the grounded jumper, you're completing the circuit back to the positive, as if you did it between the two terminal posts. I'd probably use a multimeter instead, in case it isn't enough power to make a spark.

    After that, check the ground straps and grounding points (see shop manual for locations). Then it's on to wire tracing/diagnostics. Find the wiring diagram, and follow the power from the regulator to the ignition coil. Then from there to the coil. Inspect the connectors, check for corrosion. Use continuity tester and/or ohms to see if the wire flows power. If you don't have a shop manual, I bet the H&D forums can point you in the right direction. If you've never used one, I think you'll be surprised at how much they can offer when it comes to electrical diagnosis. Acceptable voltage and ohm ranges, and sometimes useful procedural steps. Like 'if this works, then look here instead'.

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    Last edited by aldend123; 01-30-17 at 04:25 PM.
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  8. #8
    go faster cdovego's Avatar
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    Re: Help needed: Harley no-spark situation

    Random guess, is the stereo stock? Safe money says no by it frying itself. Either way I'd pull the stereo, confirm no bare wires behind it and check that off the list of questions.

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  9. #9
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    Re: Help needed: Harley no-spark situation

    Quote Originally Posted by aldend123 View Post
    Excuse me while I hang my head in shame. Seeing 13.5 I assumed that was running output. You know, besides the whole 'no spark' thing.
    I wouldn't read that much in to the dash being 10-11v then either. Maybe a little low, but tough to say if it's related. In theory, it should show roughly what the terminal posts show when your ignition is on, with the draw from the radio, lights etc. Usually reads a bit low due to voltage drop. Does seem like a big delta.

    Wouldn't that identify a short circuit, a positive wire shorting/grounding to the frame? When you contact the grounded jumper, you're completing the circuit back to the positive, as if you did it between the two terminal posts. I'd probably use a multimeter instead, in case it isn't enough power to make a spark.

    After that, check the ground straps and grounding points (see shop manual for locations). Then it's on to wire tracing/diagnostics. Find the wiring diagram, and follow the power from the regulator to the ignition coil. Then from there to the coil. Inspect the connectors, check for corrosion. Use continuity tester and/or ohms to see if the wire flows power. If you don't have a shop manual, I bet the H&D forums can point you in the right direction. If you've never used one, I think you'll be surprised at how much they can offer when it comes to electrical diagnosis. Acceptable voltage and ohm ranges, and sometimes useful procedural steps. Like 'if this works, then look here instead'.
    I was thinking my jumper cable hypothesis would mimic a good grounding strap. So, if it worked like that, then I could confidently say it's a grounding issue and chase that.

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  10. #10

    Re: Help needed: Harley no-spark situation

    More then likely a bad ground. Things tend to shake loose also.. plus corrosion. One other issue I have found because of the built in vibration factor sometimes wires my look good on the outside but be broken inside where they bend or get pinched against the frame or tank. So you need to check the continuity of each wire.. a lot of work... HD making Mechanics out of riders since 1900..
    Good luck

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  11. #11
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    Re: Help needed: Harley no-spark situation

    Quote Originally Posted by cdovego View Post
    Random guess, is the stereo stock? Safe money says no by it frying itself. Either way I'd pull the stereo, confirm no bare wires behind it and check that off the list of questions.
    It is stock.

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  12. #12
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    Re: Help needed: Harley no-spark situation

    Quote Originally Posted by MUZ720 View Post
    More then likely a bad ground. Things tend to shake loose also.. plus corrosion. One other issue I have found because of the built in vibration factor sometimes wires my look good on the outside but be broken inside where they bend or get pinched against the frame or tank. So you need to check the continuity of each wire.. a lot of work... HD making Mechanics out of riders since 1900..
    Good luck
    Thanks man, I think you're probably right. I feel like I've checked all of the other boxes.

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  13. #13
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    Re: Help needed: Harley no-spark situation

    12v directly to the coil leads to static/noise in the speakers. How is that even possible?

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  14. #14

    Re: Help needed: Harley no-spark situation

    its a ground issue and or bad coil wires..

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  15. #15

    Re: Help needed: Harley no-spark situation

    Was this bike ever repainted to your knowledge?

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  16. #16
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    Re: Help needed: Harley no-spark situation

    Thanks guys. I poked around for a few minutes but didn't immediately find anything. I probably won't be able to work on it again for a few days.

    I'm fairly certain it was repainted. Why?

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  17. #17

    Re: Help needed: Harley no-spark situation

    Well you need to take everything out of that fairing to paint it correctly plus remove all body parts. It would make sense that wires where disconnected and such. Also things might not been re installed with great care or to factory specs for that matter. And could be a reason your having your issues now.

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  18. #18
    Member ducatirdr's Avatar
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    Re: Help needed: Harley no-spark situation

    I believe the dash was black from the factory and someone wanted it to be color matching. If I were you I would take the time to clean every ground location starting with the engine to frame and all the dash to frame contacts. It's a lot of work but with the amount of oxidation on this bike I expect it was left in a temp swinging location or outside. The bike got cold and then warmed up and got cold. This attracts moisture like a cold glass of water on a warm day. Even in an unheated shed this moisture trap occurs. (use of a simple fan blowing on the bike can reduce this by quite a bit) This causes oxidation to form on the bare metal surfaces used for the electrical ground. That is a resistor. Things rust and form a gap and the temp cycles and previous vibration cause more gap. Then it finally stops working...

    Every ground location should be shiny metal. I expect it looks like the fins on that engine now.

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  19. #19
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    Re: Help needed: Harley no-spark situation

    The dash was definitely painted in-place (poor masking job), but I'm assuming the bags and tank came off. I'll be chasing grounds again some night this week.

    I grounded the coil straight to the battery, but that didn't make a difference.

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  20. #20
    go faster cdovego's Avatar
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    Re: Help needed: Harley no-spark situation

    I still say start with the stereo, more proof you may very well find a loose black ground wire dangling around behind it. Imagine if it was that easy?

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  21. #21
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    Re: Help needed: Harley no-spark situation

    I have intentionally not touched the bike for a few days. I'll get back to it on Monday, starting with cleaning grounds.

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  22. #22
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    Re: Help needed: Harley no-spark situation

    ill talk to my A tech on Tues when hes back in. maybe he can point you in a direction but wiring on those can be a bitch.

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  23. #23
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    Re: Help needed: Harley no-spark situation

    Quote Originally Posted by SVRACER01 View Post
    ill talk to my A tech on Tues when hes back in. maybe he can point you in a direction but wiring on those can be a bitch.
    That'd be awesome, thanks! I've also found (now that I'm using a high quality multimeter) that the coil reads ~12.5V for the first half second I put the leads to it and then immediately drops to 5-6V. Not sure if that's any indication of anything.

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  24. #24
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    Re: Help needed: Harley no-spark situation

    Quote Originally Posted by SVRACER01 View Post
    ill talk to my A tech on Tues when hes back in. maybe he can point you in a direction but wiring on those can be a bitch.
    Well? Well???

    I also noticed last night that the circuit breaker for the ignition was only 15A, so I put in a 30A (as spec'd) - didn't make a difference.

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  25. #25
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    Re: Help needed: Harley no-spark situation

    I'm leaning towards a ground problem
    Having owned a number of older harleys , in my experience it's always the wiring thats the weak point due to vibration.
    I had a similar issue on my old dresser and it turned out to be a bad ground , took me forever to find it,turned out it was the radio was the culprit
    I started by disconnecting everything that wasn't necessary to make the bike run and then worked backwards from there.
    Good luck , but on a positive note you own the best motor ever put out by harley , totally dead nuts reliable

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