Replacing the Spark Plugs in the V8 Lincoln LS 3.9L

By Quik LS, Jul 13, 2017 | |
  1. Quik LS
    Submitted by: Quik LS

    Replacing spark plugs on the V8 is easy to do but requires working in a tight space, while the V6 is a little more involved as it requires the removal of the intake (which is listed in a separate tech article).

    While you have access to this area, examine the coils to ensure they do not need to be replaced at the same time.

    Spark Plug

    1. Remove the ignition coil.

    NOTE: Use compressed air to remove any foreign material from the spark plug well before removing the spark plugs.

    2. Remove the spark plugs.


    3. Inspect for a bridged gap.
    • Check for deposit build-up closing the gap between electrodes. Deposits are caused by oil or carbon fouling.
    • Clean the spark plug.


    4. Inspect for oil fouling, identified by wet, black deposits on the insulator shell bore electrodes. This is caused by excessive oil entering the combustion chamber through worn rings and pistons, excessive valve-to-guide clearance or worn or loose bearings.
    • Correct the oil leak concern.
    • Install a new spark plug.

    5. Inspect for carbon fouling, identified by black, dry, fluffy carbon deposits on the insulator tips, exposed shell surfaces and electrodes. This is caused by a spark plug with an incorrect heat range, dirty air cleaner, too rich a fuel mixture or excessive idling

    • Clean the spark plug.

    6. Inspect for normal burning.

    • Check for light tan or gray deposits on the firing tip.

    7. Inspect for pre-ignition, identified by melted electrodes and possibly a damaged insulator. Metallic deposits on the insulator indicate engine damage. Pre-ignition may be caused by incorrect ignition timing, wrong type of fuel or the installation of a heli-coil insert in place of the spark plug threads.

    • Install a new spark plug.

    8. Inspect for overheating, identified by a white or light gray insulator with small black or gray-brown spots with bluish-burnt appearance of electrodes. This is caused by engine overheating, wrong type of fuel, loose spark plugs, spark plugs with an incorrect heat range, low fuel pump pressure or incorrect ignition timing.

    • Install a new spark plug.

    9. Inspect for fused spot deposits, identified by melted or spotty deposits resembling bubbles or blisters. This is caused by sudden acceleration.

    • Clean the spark plug

    10. Inspect to make sure the platinum tip is present.

    11. Adjust the spark plug gap as necessary.



    1. To install, just reverse the removal procedure.

    Editors Note: Below is a video I found of this procedure.


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