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Help, spark on number 1 cylinder only

Discussion in 'XJ Technical Chat' started by limpusfamily, Jun 10, 2011.

  1. limpusfamily

    limpusfamily New Member

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    Hello everyone, I am a new nember and was hoping all you XJ riders out there maybe able to help me.

    I have a 1981 XJ750 which was running fine until I read one of your blogs about stopping the battery sencor warning light flashing by connecting a wire from the white/ red wire (battery sencor) with a 2k ohm resister to the positive terminal of the battery. this I might add did stop the warning light from flashing but the bike hasn't run since.
    I have a manual and have checked the coils (which have power to them) checked the pickup coils, check all fuses and connections. I have 2 spare TCI boxes and have changed them around, I also have a spare regualator which I have also changed, but the bike still will not start.
    It has spark only on the number 1 cylinder

    Does anyone have any ideas as I have tried everything I can think off. I have to admit that I am no expert on electrics.

    You know what they say about experts! X is past tense and spurt is a drip under pressure.

    I am sure that it is only something very simple but I can't put my finger on it. Looking forward to your responce.
     
  2. RobDrech

    RobDrech Member

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    I would start by undoing the resistor to see if the mod is what is causing the issue.
     
  3. limpusfamily

    limpusfamily New Member

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    Thanks for your reply.

    I have disconnected the wire and resister but I must have shorted someting out as the bike still will not start, only spark on that one cylinder.
     
  4. RickCoMatic

    RickCoMatic Well-Known Member

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    The Mod IS NOT ... To the Battery!

    The Mod is: Rear Tail-light -to- Sensor Pigtail ... WITH a 2K Ohm 1/2 Watt Resistor ... Between the Tail-light and the Sensor Pigtail

    )))-Tail light --------> 2K Ohm .5 Watt Resistor >-----Sensor wire.

    The Power source is SWITCHED, Low Pwr., --- Not +12V Hot
     
  5. limpusfamily

    limpusfamily New Member

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    Thanks for the reply.

    So I misread the bit about the resistor and I have shorted something out. What have I overpowered and how do I fix it?

    I have a spare bike as parts, what part do I have to replace to get the bike up and running.

    Thanks again
     
  6. KrS14

    KrS14 Active Member

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    Kind of hard to say without some more info, as the batt sensor circuit has absolutely no relation to the starting circuits.

    First thing i'd do is charge up that battery so it's 105% ready to power that bike.

    Also, have you changed out the fuse box for modern blade type fuses? Or are you running original fusebox still?
     
  7. limpusfamily

    limpusfamily New Member

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    Thanks for you help

    The battery is new and charged, the fuses are the original but I have checked them and they seem fine.

    The bike cranks over fine but only spark on one cylinder. The spark on the number 1 cylinder is strong but none on others.

    As I said, the bike was running fine before I hooked the wire to the battery sensor. I have removed the wire to the sensor but still nothing.

    Look forward to some more ideas.

    Thanks again
     
  8. mlew

    mlew Well-Known Member

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    Get a meter and check them, just because they look good does not mean they are. Remove and clean them if necessary. Make sure you have 12 volts to the ignition circuit.
    Since you have spark on #1 you should have it also on #4 since they are the same coil. If not you have a bad coil , wire or plug cap. Check the coils and cap with a meter.
    How is the condition of the plugs? new or used.
     
  9. RickCoMatic

    RickCoMatic Well-Known Member

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    See that you have the Spark Plug Wires run correctly.
    L-1,4 / R-2,3
    Meter the Coils and Spark Plug Wires.
    It's strange to have Spark on 1 and not on 4.

    Are the Wires breaking-down and shorting-out before the charge reached the Plug?

    Do you have someone nearby that could loan you a known good-working Igniter Box to let you Plug-in for a Test?
     
  10. pirok

    pirok Member

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    If #1 has a good spark #4 should have that too! They operates in pairs.
    #1 and #4 fires simultaneously and so does #2 and #3. Even if the TCI box has an error - if #1 fires, #4 has to make a spark too.
    Examine the wire from the left handside ignition coil and the spark plugs #1 and #4 to start with.
    The resistor thing puzzles me - it should have no impact on the ignition circuit.
     
  11. limpusfamily

    limpusfamily New Member

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    Thanks guys

    I haven't had a chance to have a crack at it today
    I have checked the coils, pickup coils, ignition and changed the TCI box but I will check the fuses and go over it all again.

    Keep the ideas coming in as it maybe something simple I have over looked.


    Thanks again.
     
  12. SQLGuy

    SQLGuy Well-Known Member

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    There's only one fuse for ignition, so it's all or nothing if the fuse is bad. However, the stock fuse boxes will cause all sorts of intermittent problems. If you have only been doing spot checks, you may think you're getting spark from only one plug, when in fact you're getting intermittent spark in general.

    An easy diagnostic step would be to get a fuse holder and some alligator jumpers from Radio Shack or an auto parts store, put a 10A fuse in the holder, and then use the jumpers to bypass 12V straight from the thick Brown wire coming into the fuse box to the Red/White wire going to the coils.

    Also, read the troubleshooting guide here: http://xjbikes.com/Forums/viewtopic/p=274100.html

    As Pirok said, these plugs fire in pairs. The only ways you could have good spark from #1 and no spark from #4 would be if your high voltage wires are crossed (i.e. #4's plug connected to plug #3), or if the gap was bridged on plug #4.
     
  13. RickCoMatic

    RickCoMatic Well-Known Member

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    Begin your Troubleshooting by having you Battery Tested for AMPS.

    If you're running off the Top of that Battery, ... the Voltages drops-off fast if the Battery isn't getting a deep charge.

    AutoZone has a Tester.'
    They do it for free.
    Just bring in a Fully Charged Battery.
     
  14. limpusfamily

    limpusfamily New Member

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    You blokes out there really know your stuff. I have got my bike up and running again, the problem was low voltage from poor connections in the fuse box. I replaced the fuse box, cleaned up the wiring and she is as good as new. Well maybe not new. I have also fixed the flashing warning light, no damage done.

    Everybody who owns a xj should read the forum titled "How to: Ignition Troubleshooting" written by SQLGuy

    Thanks again and its good to know you have some support in this world.
     

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