Modern tune-ups typically involve only replacing the spark plugs and possibly the plug wires. Before performing the tune-up, you must make certain the spark plugs are properly gapped. Improper gapping can lead to poor engine performance.
The section of the spark plug that is inside the engine has two main components: ground electrode and center electrode. The ground electrode is the hook portion and the center electrode is the one protruding from the center of the spark plug. The space between these two electrodes is the spark plug gap.
The proper gap for a 3.8-liter Ford Mustang is .054 inch. This gap is checked by placing a feeler gauge or a spark plug gapping tool between the two electrodes. If the spark plug is .002 inch or more too wide or narrow, slightly pry upward or push downward on the ground electrode to adjust the gap.
Some spark plugs are non-adjustable. These are typically multi-electrode spark plugs. Make certain to thoroughly read the spark plug's instructions prior to attempting to adjust the plug gap.
Some spark plugs may have a note on the box claiming to be "pre-gapped." Regardless of the plug coming with this notation, always check the gap and adjust it if needed.
