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.
Removal & Installation
4.6L, 5.4L & 6.8L Engines
- Disconnect the negative battery cable.
Remove the coil on plugs as outlined under Ignition Coil in this section.
NOTERemove any foreign material from the spark plug wells with compressed air before removing the spark plugs.
- Remove the spark plugs.
- Inspect the spark plugs
- Adjust the spark plug gap as necessary. Proper gap is 0.52-0.56 in. (1.32-1.42mm).
- Install the spark plugs and tighten them to 13 ft. lbs. (18 Nm) for 4.6L and 5.4L SOHC engines. For 5.4L DOHC and 6.8L engines, tighten the spark plugs to 15 ft. lbs. (20 Nm).
- Install the coil on plugs.
- Connect the negative battery cable.