Pulse generator

Discussion in '1st & 2nd Generation 1983-1989' started by a1gatorz, Mar 2, 2015.

  1. JasonWW

    JasonWW New Member

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    I may have some bad news. I found a similar thread on these forums where an 87 bike had really weak spark and the pulse generators measured 270-280 ohms. He swapped in a set that were within spec and the spark became healthy again.

    So there seems to be a direct relationship between the signal strength from the PG's and the strength of the spark. Until now we were thinking the PG's only supplied a signal to the ignition box and the strength of the signal did not matter much, but it seems we were wrong.

    From doing a lot of reading I've also learned the air gap between the pulsers and the metal trigger is also very important. Most specs seem to say 0.012"-0.017" or 0.3mm-0.4mm. Any bigger and you sometimes lose some performance and or spark energy.

    So I hope you can double check the PG resistance and it actually reads in spec, otherwise you really might have 6 bad units.
     
  2. a1gatorz

    a1gatorz New Member

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    Thank you so much for that Jason ! Because let me tell you , I was really starting to think I was going bonkers ! Even more so since I rechecked all six again with a buddies high dollar meter & got exact same readings . Like the ones your talking about , its looking more & more that when they do fail. They seem to be failing in pairs ? As odd at that seems to be to us all ? I'm planning on checking all the other things we discussed today . Where did you find the info on the air gap ? I haven't come across anything like that in my manuals . I don'r quite understand how to adjust that ? Also you mentioned earlier that theirs a thread with all the known misinformation printed in the manuals ? Can you send me a link ? Looks like I need to track down a good pair of P\G's .
     
  3. NormK

    NormK New Member

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    We recently had a problem with the air gap on the pulse coil on an Enfield , closed it up slightly and problem solved
     
  4. JasonWW

    JasonWW New Member

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    The air gap is not mentioned in a lot of manuals because the factory sets them up so you can't really adjust them, but like any mass produced product the tolerances can vary. If you loosen all 7 bolts/screws I'm sure you can move it a tiny bit. Certain Honda manuals from the early 80's, as well as other brands, would list the air gap. It's also possible that newer bikes are more tolerant of the air gap than older ones, so the factory omits the air gap data.

    Due to the strong magnets, you would need a set of brass feeler gauges or you could measure a single business card and use it as a gauge. Basically, the closer the gap, the stronger the pulse/spark. You just need to allow for metal expansion once it all gets nice and hot.

    I'll try and search for the factory service manual errors, but it's a hard search subject.
     
  5. JasonWW

    JasonWW New Member

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    Here is a small sampling of pulse generator resistances:

    A1gatorz has 6 of the 87 PG's that all measure between 260 and 380 (is that right?).

    Artee has an 87 bike and he said his were in the factory 450-550 range and his bike runs fine.

    Another member, Fatso1277, had an 87 bike with weak spark and the PG's measured 270-280 ohms. He swapped them for a set with factory specs 450-550 and the spark got way better, but the engine had other problems and never ran so it's hard to draw a conclusion on this one.

    Joe has an 88 and 89 set from good running engines and all 4 measure 290-300 ohm.
     
  6. JasonWW

    JasonWW New Member

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    From what I can gather, the 86 (and older VF750 bikes) used 450-550 ohm PG's and the 88-89 bikes had 200-400 ohm PG's.
    What if the 87 bikes were a transition year with early bikes having 450-550 ohm PG's and later bikes having 200-400 ohm PG's?

    Here's a theory.

    The 86 bike has similar crank triggers and PG specs to the earlier 1st gen V4 bikes, but with a different ignition box and 4 separate coils. Factory's typically carry over parts if possible.

    In 87, they came out with a more advanced ignition box with newer style crank triggers, but they carried over the older 450-550 ohm PG specs until mid year when they switched the spec to 200-400 ohm. The 87 PG's I've seen in pictures sure look the same as the ones Honda used in the VF750 and VF1000 from 84-86. Not the big mounting bracket, but the small mounting tabs. It's feasible Honda made a new big bracket for the 87 bike and used older PG mounted to it. Especially if they had a large surplus of old PG that they needed to get rid of.

    Thats why all the 88-89 bikes have 200-400 ohm PG's while the 87's seem to have both 450-550 ohm as well as 200-400 ohm PG's.

    Just a theory.
     
  7. a1gatorz

    a1gatorz New Member

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    Jason , I must admit something SCREWY is going on hear ! I can't for the life of me understand why so many sets of P\G's are falling in the 300 ohms range ? Across so many different bikes & owners ? I do know that both the Clymers & Haynes state " L models 200-400 ohms & all other models 450-550 ohms " . The factory Honda manual for my model VFR700F2 H only states for my specific bike at 450-550 ohms . Where are you finding 88-89 readings ?
     
  8. a1gatorz

    a1gatorz New Member

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    Well I am now more confused then ever . I hate to say it , cause it really IRKS me to be beaten on something with my own bike ! I'm to the point off raising both arms & crying UNCLE . A local repair shop has quoted me no more then 2 hours ( at $85 an hour ,very reasonable ? ) to diagnose my problem . I'm feeling very defeated right now . What do you guys think ? The closer I'm getting to summer the more it hurts to not have my baby up & running ?
     
  9. NormK

    NormK New Member

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    I would be surprised if the shop would sort it out in 2 hours, if they can't buy new pulse coils then they are no further ahead than you are at this stage. I ask the question once again have you tried testin the coils as I described earlier, until you do that you are not able to prove anything regarding how good the spark is. If the spark is good with this test I will then agree that the pulse coil or ignition box can improve the spark, till then I'm not convinced, but glad to be proven wrong if it helps
     
  10. NormK

    NormK New Member

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    Ok so does anybody know if this coil system is Kettering or CDI?, not sure if it would make any difference but can somebody explain to me how the pulse coils can control how much spark a coil can dump? I would love to know
     
  11. a1gatorz

    a1gatorz New Member

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    Not having my own oscilloscope , I'm left to do the best I can . Maybe the shop does ? Couldn't hurt for me to ask ?
     
  12. NormK

    NormK New Member

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    I won't mention testing the coils again you obviously don't thing it is important
     
  13. JasonWW

    JasonWW New Member

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    Joe has an 88 and 89 set from good running engines and all 4 measure 290-300 ohm.

    Maybe we should start a new thread just to get folks to test their PG resistance on known, good running bikes. Or we can start a poll and form a database.
     
  14. JasonWW

    JasonWW New Member

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    It's definitely Kettering, you can tell by the wiring diagram. The ignition coils have a constant 12v source which means the ignition box has to send a brief ground signal to collapse the coil and produce a spark. It's similar to a points setup, but the points are replaced by transistors where it gets the name TCI or Transistor Controlled Ignition.

    CDI ignition coils are not powered all the time. Their igniton box puts out a short positive burst of power which is then amplified by the coils.

    I'll have to get back to you about how the PG strength effects the spark strength as I'm just not that familiar with the inner workings of the ignition box.
     
  15. JasonWW

    JasonWW New Member

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    I sent a email to Rae-San Electronics as he is familiar with several honda bikes from the 80's and speaks english. Same language always helps. :) Hopefully he can shed some light on this PG resistance issue.
     
  16. JasonWW

    JasonWW New Member

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    Okay, I just heard back from Rae-San. He essentially says that the pulse generators are an on/off signal and that the resistance has no effect on the spark strength. He further explains that the 86 bikes with only 2 crank triggers can use the higher resistance PG's and that the 87-89 bikes, that have the 11 crank triggers, will need a lower resistance PG in order to be more sensitive. So I'm betting the manual is wrong and that 87-89 bikes PG should measure 200-400 ohms (Which they all do except for Artee's bike. Maybe we can get him to measure it again?)

    Below is a copy of the letter if you want to read all the details. My parts are colored blue:

    Hi,

    I'm working with a group of fellow's on the Honda VFR700/750 bikes from 86-89. As you know these are the 180* crank bikes with 4 coils. The 86 bikes seem to have a unique ignition box just for it using a camshaft sensor. The 87-89 don't use a cam sensor, thier ignition box is different internally and their crank triggers are very different from the 86 as well.


    The 86 I think uses a single bump on the crank sensor (NOTE: I believe he's confusing the 86 bike for the oolder 1st gen engines that use the dual coils and 360* crank) - this is fine for a 360deg crank where you can do wasted spark and fire on both the compression and exhaust strokes - with the 180 crank - you need to be able to tell which stoke you are on to fire the correct cylinder - hence 4 coils instead of 2 used on the 360 degree crank models.
    This is the "cam" sensor - the crank tells when to fire, the cam tells which one of two to fire.

    note that in this case there is only one pulse from the pickup per crank revolution - these are the higher resistance ones.
    We are all a bit confused with the pulse generator resistance measurements. Our Service manuals state the resistance should be between 450-550 ogms on all years 86-89. We have tested quite a few and the 86 bikes seem to be in that 450-550 range, the 88 and 89 bikes seem to be around 290-300 ohm and the 87's are a mixed bag. Some are 260-370 and others are 450-550.

    Now the 87-89 - i speculate here - but without a cam sensor I would assume they use a crank sensor with several; smaller bumps, probably with one missing - usually about 7 at spacing for 8. the missing bump is used for absolute crank position determination and then the computer
    works out which one to fire with the bumps -
    these bumps come more often - for the same rpm - and hence the pickup coil needs to be "faster" - to do this it ends up being a bit lower in resitance due to the need for less turns - it will probably generate a bit less voltage - but the computer / ignition will be designed with that in mind.

    It's really confusing us. On one hand, if the bike runs well with pulse generators in the lower range, then fine. they are working, but would the spark energy be a bit low?

    no - spark energy is a function of the dwell and coil current only - not the pickup coils.

    If we swapped in a higher resistance set would that increse the spark energy?

    Nope - they only act as triggers and the higher resistance ones would react a bit more slowly - resulting in a bit of retard on the timing -
    possibly not noticeable - Id have to measure one to work that out.

    Or do the pulse generators only act as a signal to the ignition box, like an on/off signal?

    yep

    Any help here would be appreciated.

    Thanks,
    JasonWW

    hth
    Ray
     
  17. NormK

    NormK New Member

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    Thanks Jason, exactly as I thought, now I wonder if a1gatorz will do as I have been banging on about and test the coils, plugs,plug leads and plug caps, and can you thank Rae-San for his efforts
     
  18. JasonWW

    JasonWW New Member

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    I told A1gatorz to at least measure the coil voltage while cranking. I read about a guy who had all sorts of no spark problems and he kept messing with it for years and then he put a new battery in and it fired right up. :hss: His old battery would crank over the engine, but the coil voltage was too low to actually fire it off. People told him to measure the coil voltage while cranking, but he skipped that step.
     
  19. NormK

    NormK New Member

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    Yup, I have seen batteries drop to 8 volts when cranking and that just isn't good enough to fire a spark
     
  20. JasonWW

    JasonWW New Member

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    Roger, your bike is an 87, right? Do you think you could measure your PG resistance?
     
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