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FJ600 Pickup Coil Question

Discussion in 'XJ Technical Chat' started by Phenromedes, Nov 4, 2021.

  1. Phenromedes

    Phenromedes New Member

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    Hello all,

    I'm in the process of restoring my '84 FJ600 and have run into an ignition issue. I get spark on plugs 2 and 3, but not 1 and 4. Following the How To: Ignition Troubleshooting, I've just completed the test of swapping orange and grey on the 6-position TCI connector, and the problem did indeed swap.

    At this point, it appears the problem is the pickup coils, per that guide. The issue I have is that, when following my Clymer manual's testing procedure for the pickup coils, I get the correct 120ohm+/-20% reading on both orange-black and grey-black.

    So I have two questions, born out of the lack of availability of pickup coils for a 1984 FJ600:
    1: Is it possible for the pickup coils to give the correct ohm readings and still be faulty?
    2: Is there a separate component on the bike called a "pickup" that is NOT the pickup coils?

    Thanks in advance.
     
  2. Jetfixer

    Jetfixer Well-Known Member

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    Not sure if they fit an FJ600 but my Seca's run Honda CB750 coils these swapped right in and have replaceable wires can still be bought new ...cheap. I don't recall checked ohms all I know is they work great .
     
  3. jayrodoh

    jayrodoh YimYam Premium Member

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    I believe he’s referring to the pickup coil, swapping the pickup output to the TCI moved the problem from 1&4 to 2&3.

    I’ve never seen one ohm out okay but not work, is it mounted securely and in the right spot? I don’t know if that bike is similar to my XJs but I’ve easily broken a mount by turning the crank with a crescent wrench.

    There is a “pickup” but generally it’s one piece rotor that triggers both coils 180 degrees out. Again not familiar with that bike but I suspect it’s the same. Got a pic?
     
  4. Simmy

    Simmy Well-Known Member

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    The later model 600’s went to single pickup coil.
    You’re not using a later TCI by any chance? They’re obviously not compatible
     
    jayrodoh likes this.
  5. Phenromedes

    Phenromedes New Member

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    I've attached a picture of my pickup coils mounted. The lower right, orange wire coil is the one that seems to be failing. Visually checking the gap, both seem to be good.

    I'm pretty sure this is the right TCI, as it's TID14-31 on a green/white sticker, which matches what Chacal has in his ignition guide, and a few other resources.
     

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  6. Rooster53

    Rooster53 Well-Known Member Premium Member

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    If this is like the earlier version of XJ's the TCI when only one pickup is functioning will fire the opposite cylinders. So if 1,4 pickup is the only working pickup, then 2,3 cylinders will fire - and yes it will backfire like crazy with this situation. Does it start and run on two cyclinders?

    Yes, it can be shorted to chassis preventing the signal from triggering the TCI. So be sure to check to chassis with it disconnected from the TCI - it should be open

    Also, does it have a rev limiter as indicated by a Y/B wire on the six pin TCI connector? I think some of the older versions of limiters cut spark to just
    two of the cylinders.
     
  7. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    Possible, but not probable, especially if the engine exhibits this problem at all operating temps (from cold start all the way to fully warmed).


    No, although PICKUP coils and IGNITION coils can get confused when just the word "COILS" is used.


    This actually sounds like an ignition coil issue, I would test those and/or check for pinched/broken/etc. wiring between the TCI output harness and the ignition coils input.....even though your results seem to negate that possibility. But ignition coil failure is much more common than p/u coil failure.

    QUESTION: did the engine ever run correctly previously? And if so, what changes/work was done on the ignition system/wiring betwene the time it worked and now-doesn't-work condition?
     
  8. Rooster53

    Rooster53 Well-Known Member Premium Member

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    I meant to add this earlier, the 49A-10 on the reluctor should match the TCI number, which I believe it will if you have the green / white sticker as described.
     
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  9. Phenromedes

    Phenromedes New Member

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    It does not run on two cylinders, but does crank and spark. I've only got spark on 2/3, but not 1/4 unless I switch orange and grey on the 6-position TCI connector. I also have attached a picture of my TCI box, which does show a Y/B wire, but I don't think I understand what you mean about shorting to the chassis. If I disconnect the pickup coil connector (4-pin TCI connector) from the TCI, I get 120 ohms between orange/black and grey/black. This is in line with what the Clymer says should happen.

    I don't think it's the ignition coils, as I just installed the set HCP24241SET from you that I recently ordered, and they bench tested perfectly, with 2.8-ish primary and 13k secondary. The bike has not run recently. It sat for 10 years, and I'm in the process of doing a resto-mod on it. I didn't try to start it before tearing it down because of how rusted the tank was.

    This is correct. I've attached a picture.
     

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  10. Rooster53

    Rooster53 Well-Known Member Premium Member

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    I should have looked a bit closer earlier, but I believe the troubleshooting guide you are using is confusing the issue. The XJ that was used for that guide is an 82 750 Seca, and it has the pickup coils on the 6 pin connector.

    https://www.xjbikes.com/forums/threads/how-to-ignition-troubleshooting.21932/#post-185964

    The drawing I have shows the FJ600 pickup on the 4 pin connector, and you just confirmed that above.

    So, what you have proved so far is that the ignition coils, plug wires, and associated wiring with the ignition coils are working. What you have isolated to is either a bad channel in the TCI, a bad pickup or wiring, or still a possible issue with the rev limiter messing with the TCI.

    With the pickup connector unplugged from the TCI measure from the gray and orange wire to a good chassis ground - it should be open as the pickups are isolated from chassis.

    To continue with the troubleshooting if the pickups ohm OK and open to chassis you could then swap the orange and grey wires on the 4 pin connector. If the same plugs (2,3) still spark then there is a bad channel in the TCI, or as said above the Rev limiter is shutting it down.

    I don't really know how the Rev limiter works in the FJ so just guessing here, but I personally would try removing the Y/B wire and see if the TCI comes to life.
     
  11. Phenromedes

    Phenromedes New Member

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    This may have been an exercise in stupidity on my part. Doing some continuity tests, I found that I had continuity through the fuse box with the fuses removed. That led me to test continuity between a few other places, including from battery + to the chassis, and there was continuity there, which I believe is really bad. In addition to this, a used TCI box arrived last night, and, after swapping that in, I had spark on all four plugs. This goes against the test results I've seen so far, so I'm very confused. I think, at this point, I need to ensure I have no bad ground, so I just need to find out where the ground wire near the battery box needs to terminate.
     
  12. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    I researched this topic a bit when trying to figure out TCI's, and this is what I found, it probably works the same way on all Yamaha models that have this feature (some XJ900's do use a rev-limiter):

    https://jetav8r.com/Vision/IgnitionFAQ.html#a6p0


    6.1 THE REV LIMITER

    The VISION has a "REV-LIMITER" circuit that kills the FRONT coil ignition if the TACH reads over 12,000rpm. The TACH reads the fire pulse from the TCI to the REAR coil. If the circuit malfunctions you'll most likely lose the FRONT CYLINDER ONLY.


    6.2 DISCONNECTING REV LIMITER

    *** CUT YELLOW/BLACK striped WIRE in 6-prong plug at TCI!! *** (Tape the ends)



    6.3 HOW TACH & REV LIMITER WORK

    The Tach has 4 wires connected to it:
    BROWN = +12 volt Power
    BLACK = -12 volts Ground
    GRAY = Ignition pulse signal that the tach reads. It is a splice "tap" off the Gray wire from the TCI to the REAR cylinder coil.

    ** That's why if you lose the rear cylinder ignition you lose the TACH. **

    The GRAY wire signal from the TCI is a "square wave" trigger to the Coils primary winding. It is normally "near" ground and the trigger is +12v to fire the coil and pulse the tach.

    To be exact: in the Tach I dismantled the GRAY wire became ORANGE after the 3-prong connector block outside the instrument cluster (contrary to every wiring diagram I have).

    YELLOW/BLACK stripped wire = this is the Rev-Limit connection. This is a single wire between the Tach and TCI. When the "Rev-Limiter" switches ON (IN THE TACH) it grounds the YELLOW/BLACK wire.

    You can try this yourself: at the TCI disconnect the YELLOW/BLACK wire in the 6-prong plug in the side of the TCI. Then while the bike is running, ground the pin where the YELLOW/BLACK wire would be connected. It causes the same thing:

    The "Rev-Limiter" KILLS THE IGNITION to the FRONT CYLINDER coil.

    If you're curious how I know this... I connected an "oscillator" to the Tach, powered it up and ran the tach up to... well, pegged it. It thinks it's connected to the engine. At 12,000 exact it grounds the Y/B wire.


    6.4 INSIDE THE TACH

    Inside the Tach are 2 small separate circuit boards. One is the Tach. And the other is obviously this "Rev-Limit" switch. I say "switch", but this is a "solid-state" switch (NOT a mechanical one). An IC chip on this board is obviously counting RPM. Now WHY Yamaha put the rev limiter in the Tach?

    I have no idea. In most systems its INTERNAL to the TCI since it is already doing "THE MATH" in the timing chip. But this was early generation stuff and maybe they couldn't pull that info "OUT" of the timing chip. So instead of adding ANOTHER rpm counting circuit to the TCI they just used the one they had to put in the Tach anyway.
     
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