3.2 Ignition System Visual Inspection

The spark plug wires, the distributor cap, and the distributor rotor are subject to wear and electrical breakdown. This will impair their ability to deliver a crisply timed and powerful spark. Many of these conditions are most easily detected by a thorough visual inspection. Dirt and moisture on these components are also potential causes of poor spark at the spark plugs.

To check the distributor cap and rotor, remove the cap as described in 5. Distributor. Inspect the contacts inside the distributor cap and at the tip of the rotor for corrosion, wear, or pitting. Corroded contacts can be cleaned and reused, but for wear, pitting, or heavy corrosion, replacement is recommended. The center black carbon brush inside the cap should spring back when compressed.

Cracks or carbon tracks in the distributor cap may cause shorts to ground. The cracks may be fine and difficult to see. Carbon tracks are faint black lines, usually running between two contacts or to ground, left over from high-voltage arcing. Replace a cap that shows any sign of cracks or carbon tracking. For a thorough inspection, be sure also to check under the black radio-suppression shield on the outside of the cap.

To check the spark plug wires, gently bend them in several places to expose cracks in the insulation which may cause spark "leaks." Remove the rubber boots and check them for pliancy and the ability to seal out dirt and moisture. Replace any wire that is cracked, oil-soaked, or dry and brittle.

For a quick-check of the distributor cap and spark plug wires, listen for the sound of the arcing or watch while the engine runs at night. The arc of high voltage to ground because of a crack in the cap or a poorly insulated wire may be visible as a blue spark. Also, use a spray bottle to spray a fine mist of water around the cap and wires while the engine runs. If the cap and wires are in good condition and insulated properly, the added moisture should have no effect. If their condition is marginal, the added moisture may promote arcing and cause the engine to run roughly.