300M, Concorde, Intrepid, LHS, 1998-2004

Spark Plugs


Inspection & Gapping

Check the plugs for deposits and wear. If they are not going to be replaced, clean the plugs thoroughly. Remember that any kind of deposit will decrease the efficiency of the plug. Plugs can be cleaned on a spark plug cleaning machine, which can sometimes be found in service stations, or you can do an acceptable job of cleaning with a stiff brush. If the plugs are cleaned, the electrodes must be filed flat. Use an ignition points file, not an emery board or the like, which will leave deposits. The electrodes must be filed perfectly flat with sharp edges; rounded edges reduce the spark plug voltage by as much as 50%.

Check spark plug gap before installation. The ground electrode (the L-shaped one connected to the body of the plug) must be parallel to the center electrode and the specified size wire gauge (please refer to the Tune-Up Specifications chart for details) must pass between the electrodes with a slight drag. NEVER adjust the gap on a used platinum type spark plug.

Always check the gap on new plugs as they are not always set correctly at the factory. Do not use a flat feeler gauge when measuring the gap on a used plug, because the reading may be inaccurate. A round-wire type gapping tool is the best way to check the gap. The correct gauge should pass through the electrode gap with a slight drag. If you're in doubt, try one size smaller and one larger. The smaller gauge should go through easily, while the larger one shouldn't go through at all. Wire gapping tools usually have a bending tool attached. Use that to adjust the side electrode until the proper distance is obtained. Absolutely never attempt to bend the center electrode. Also, be careful not to bend the side electrode too far or too often as it may weaken and break off within the engine, requiring removal of the cylinder head to retrieve it.

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Fig. Inspect the spark plug to determine engine running conditions

Removal & Installation

2.7L, 3.2L And 3.5L Engines

The V6 engines use platinum resistor spark plugs.

Extreme care must be used to prevent spark plug cross threading, mis-gapping and ceramic insulator damage during plug removal and installation.

Cleaning of the platinum plug may damage the platinum tip.

Always remove the ignition coil assembly by grasping at the spark plug boot, turning the assembly 1/2 turn and pulling straight back in a steady motion.

  1. Disconnect the negative battery cable.
  3. Remove the intake manifold.
    Prior to removing the ignition coils, spray compressed air around the coil area, spark plug and spark plug tube.

    On 3.5L engines, it is necessary to loosen the screws by alternating back and forth. Do not lose the spacers under the coil when loosening the screws.

  5. Remove the ignition coil.
  7. Remove the spark plug using a quality socket with a rubber or foam insert.
  9. Inspect the spark plug condition.

To install:

  1. Install or connect the following:
    To avoid cross threading, start the spark plug into the cylinder head by hand.

    On 2.7L Engines Tighten to 12.5 ft. lbs. (17 Nm).

    On 3.5L Engines Tighten to 20 ft. lbs. (28 Nm).

    Tighten spark plugs.

    Install ignition coil assembly onto spark plug.
    Hand tighten coil screws.
    Tighten ignition coil screws to 60 inch lbs.( 6.7 Nm).
    Connect and lock the electrical connector.
    Install the intake manifold
    Connect the negative battery cable.