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Low voltage on red/white ignition wire

Discussion in 'XJ Technical Chat' started by Johnc2432, Oct 11, 2020.

  1. Johnc2432

    Johnc2432 New Member

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    Hi all
    I'm renovating my brothers old xj650 which hasn't moved since 2004.
    There is no spark at any of the plugs. I have multiple new batterys and cleaned up every connection and earth I can see.

    I have 12.8v at battery but only 9.7v at thd ignitor red/white wire.
    When I unplug the coils I get 12.8v on thd red white wire.

    I dont get a spark when turning over ( I use a spark testing light) but it does singularly spark when the ignition is turned off.

    Is this tci fault? It seams unlikely 2 coils fail ssmd time. Why would coils be drawing hhd voltage down so much?

    Both the coils and tci get warm. I expect the coils to get warm , but tci??

    Can the tci fail in a way that the coils draw more because the signal wire is giving faulty signal?

    What does the spark at ignition off signify?

    Thanks

    John
     
  2. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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  3. Johnc2432

    Johnc2432 New Member

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    Hi, Fuse box has been replaced with new blade fuse box. The wiring generally is all good and complete with hardly any volt drops across switches connectors. This is how I have got down to coils or tci. Its just unusual in my mind for 2 coils to not work at same time, but when I connect up thd coils voltage on the red/white wire drops from 12.8 to 9.7 .
    In my mind then the coils are dropping the voltage, but may not be the fault of the coils if the coils are being asked to do something by the TCI that causes thd drop??
     
  4. Franz

    Franz Well-Known Member

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    Are the grounds to the coils clean the one that attaches the coil to the frame?
     
  5. Johnc2432

    Johnc2432 New Member

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    Yes. I cleaned them back today and the earth wire terminal. I thought that too. Voltage the same as before.
    Thanks
     
  6. Franz

    Franz Well-Known Member

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    Have you tested the battery voltage under load when cranking the engine? Think it needs to be about 10 volts to make the TCI transistors work. The TCI has two transistors one for each coil so even if one had failed one ignition coil would be working. Unlikely it is the TCI, do you have a sidestand switch and if so have you checked the connectors on that?
     
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  7. Johnc2432

    Johnc2432 New Member

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    The 9.7v reading was taken with new battery ignition on. I haven't measured whilst cranking. I also supplemented the battery with a car battery via jumper cables to see if different result. It wasn't.

    There is no sidestand switch or clutch switch both were removed a long time ago when the bike was running daily. Looking at wiring diagram there is a white/black wire going from side stand relay to TCI. Looks like that is ground side of the switches so when switches removed should be grounded to the frame or just disconnected?
    That wire goes to the connector on the TCI that also has the signal pick ups so maybe that wire if isn't properly grounded it interrupts the signal in , so doesn't signal out to coils?
     
  8. Franz

    Franz Well-Known Member

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    The black wire with the white stripe. I disconnected that from the TCI and my engine started. I think when it's connected to the TCI it stops the bike starting when the sidestand is down. The relay is normally closed it opens when the sidestand is down to cut the power. As you don't have them now and you are getting power to the coils must be something else.
     
  9. Franz

    Franz Well-Known Member

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    You could try disconnecting the black white stripe wire to the TCI .
     
  10. Polock

    Polock Well-Known Member

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    the tci opens/closes the (-) to the coils. it gets it's signals from the ignition pickups down on the crank. 3 wires from the pickups, one common and another for each pickup.
    measure the resistance of those wires to each other. none of those wires should have any connection to ground.
     
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  11. Rooster53

    Rooster53 Well-Known Member Premium Member

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    If the coils are pulled low by the TCI and you remove power it is normal for the plugs to spark one time.

    Your coils should not be heating up if the TCI is working correctly. If they are getting warm with just the key on then that indicates that the TCI output transistors are either commanded always on or shorted.

    With ignition on bike not running:

    Check the Orange and Gray (ignition coil low side) wire on the TCI 4 pin connector, they should be close to battery voltage after the switch has been on for over 3 seconds.

    If they are both reading approximately 1.3 VDC, then the output transistors are conducting - try grounding the B/W wire that goes to the TCI - do the Orange and Gray wires go high near battery voltage? If so, then the TCI is not functioning correctly internally, if they remain low at 1.3 VDC then the output transistors are likely shorted or a wiring error is present.
     
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  12. Johnc2432

    Johnc2432 New Member

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    Just to close this thread. I found an exact part number tci on ebay for £29 and took a punt.
    Now havd spark and 12.8v on red wire so tci was faulty.
    Thanks all for comments
     
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