Factory Specifications for Mustang Spark Plug Gaps

by John Walker
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Spark plugs are the igniter within an engine. The gap on a spark plug is the distance between the electrodes. Electricity running through the plug will arc over the gap igniting the fuel in the engine. The proper gap ensures that the fuel will ignite each time. The average gap is 0.035 and 0.045 thousandths of an inch. Ford Mustangs raise that level just a little bit.

Factory Recommendations

The Ford recommended spark plug gap for the Mustang engine is 0.054 thousandths of an inch. You can measure the gap on the plug using a gap gauge available from any auto parts retailer. Adjusting the gap too high can cause misfires in the engine. Too low of a gap will result in a weak arc, which also can cause misfires. Aim for between 0.052 and 0.056 thousandths of an inch. Use the gap gauge to bend the arm on the spark plug out if the gap is too small. Lightly press the arm down with your finger if the gap is too large.


Routine maintenance with regard to the spark plugs occurs every 20,000 to 30,000 miles. You should check the wires, plugs, and distributor, if installed. Look for cracked or separated wires on the plug wires. Inspect the interior connection for signs of corrosion on the wire on both ends of the wire. Replace any damaged wires. Look for signs of soot, oil, carbon buildup, or physical damage to the plug. Soot, carbon buildup, and oil indicate excessive firing or weak seals. Physical damage can be the result of extreme explosions within the chamber. You should contact a mechanic for a full inspection at that point. Replace damaged or fouled plugs immediately. Always work on one plug at a time to avoid connecting the wrong wires.


Generic or stock spark plugs for four- and six-cylinder engines need to be gapped. Most spark plugs for eight-cylinders come pre-gapped but you should check them. Several aftermarket performance plugs are pre-gapped at the proper levels to allow for optimum performance. Platinum and iridium plugs offer more stable and consistent spark improving performance and gas mileage. The upgraded plugs are available for all makes and models of engines.

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