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power loss and tachometer indication loss

Discussion in 'XJ Technical Chat' started by Planehue, Jun 17, 2010.

  1. Planehue

    Planehue Member

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    83 xj750 stock
    On my way to work today I lost power and my tach went to 0 and stayed. I played with the fuel, no change. I had been on the road for at leasst 15 minutes. I could get to speed just real slow. No back fire or popping.
    I started it up after 2 hours. It started fine but only ran on the out board cylinders, 1 and 4. Tach still did not indicate. I am thinking it is a bad ignition coil as that is all that I can see is related to all three items, cylinder 2, 3 and the tach. Do the coils just go bad or is there a possibility it could be wireing?
    Thanks
     
    Planehue, Jun 17, 2010
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  2. skippy344

    skippy344 Member

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    Yes, the coils can go bad, but the TCI can also cause the same troubles.

    Something as simple as wiring to any of these devices can cause issues like that.

    Do a quick look over of all the wiring connectors and wires to the coils, TCI and from the alternator.

    If all that "looks" ok, then its time to start testing the ignition coils with an ohm meter.
     
    skippy344, Jun 17, 2010
    #2
  3. Robert

    Robert Active Member

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    On the 750, the tachometer gets it's input from the TCI. Given you have lost your tach input, I'm wagering your TCI just took a dump. Go ahead and verify the coil resistance values (2.25 to 2.75 ohms on the primary winding and 11k ohms on the secondary) and ensure that the coil wiring to the TCI is sound. Swap coil inputs and see if the problem follows the input, you know it is the TCI or upstream issue. If the problem stays with the 2-3 coil, you have your problem. Another culprit could be the ignition pick-up coils (780-520 ohms) and associated wiring (the inputs to the TCI). That will help determine what exactly is wrong so you can start the repair.
     
    Robert, Jun 17, 2010
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  4. Planehue

    Planehue Member

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    Thanks for the input. Might not get to it till I get home tonight. Then I will start the trouble shooting and let you know
     
    Planehue, Jun 17, 2010
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  5. Planehue

    Planehue Member

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    I looked at it at my lunch. I could not find any visibly loose wires. I checked the values - L/H coil (1&4) pri = 2.9 sec = 15.58 . R/H coil (2&3) pri = 2.9 sec = 22.64. After I put them all back on everthing worked great. I will be doing some good cleaning tonight of all the connections. Thank you very much Skippy344 and Robert your input helped greatly on the troubleshooting.

    Hugh
     
    Planehue, Jun 17, 2010
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