The proper operation of the spark plugs is vital to good engine performance and economy. Use the correct plugs as listed in the specifications. On 1970 through 1974 models, check the gap and the condition of the spark plug electrodes each 6000 miles. Install new spark plugs each 12,000 miles. The fuel injection engine introduced in 1975 used long-life spark plugs. You need only replace such spark plugs each 15,000 miles. Adjust the gaps of the new spark plugs before you install the plugs in the engine. The correct gap for 1970 through 1974 engines is 0.60 mm (.024 in.). The correct gap for fuel injection engines is 0.70 mm (.028 in.).