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Compression Test

Discussion in 'XJ Technical Chat' started by shnuffy, Apr 8, 2010.

  1. shnuffy

    shnuffy Member

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    Hey all, apologies for redundancy of this thread, but the search needs work! Like the ability to search "Topic Titles" ONLY instead of "Topic Titles & Message Text" or just "Message Text." Anyway...

    I want to do a compression test soon. How do I do this? My dad tried years ago but couldn't get the gauge to stick, he figured he need the YICS tool. Is this required? What else might cause the gauge to consistently fall to 0?

    My idea of the process is as follows:

    1. Pull all plug wires.
    2. Pull number 1 plug and install compression gauge, leaving plugs 2, 3 and 4 in their cylinders.
    3. With full throttle, turn the motor over until the gauge stops rising.
    4. Record results.
    5. Repeat for cylinders 2, 3 and 4.

    Am I missing anything here?

    Hopefully this will serve future XJ newbs! :)
     
    shnuffy, Apr 8, 2010
    #1
  2. dawsoner

    dawsoner Member

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    +1
     
    dawsoner, Apr 8, 2010
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  3. iwingameover

    iwingameover Active Member

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    Unplug the TCI or you could get a shock from your plug wires. You also don't want it to start. Just turn over about 10 times.

    YICS shouldn't need blocked off for a compression test.

    If you gauge goes to 0 without releasing it then it's bad or has a crack in the line.
     
    iwingameover, Apr 8, 2010
    #3
  4. shnuffy

    shnuffy Member

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    Sounds good. The TCI is the main electrical connector? What does it stand for?
     
    shnuffy, Apr 8, 2010
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  5. iwingameover

    iwingameover Active Member

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    Transistor Controled Ignition. It's under the left hand side cover.
     
    iwingameover, Apr 8, 2010
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  6. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    You don't leave any plugs in their cylinders.

    Remove ALL spark plugs.

    Unplug TCI (ignition module.) Not to prevent shock but to keep from burning it up trying to fire missing (ungrounded) plugs.

    Attach gauge.

    (assuming fresh battery) hold throttle wide open and crank motor about 4-5 revs should do it before it stops rising. If the needle in your gauge just falls back down, it's the gauge. The gauge should hold the reading until you "release" it.
     
    bigfitz52, Apr 8, 2010
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