The distributor cap should be removed for visual inspection. Check the cap for:
Inspect the distributor cap and rotor. Courtesy of American Honda Motor Co., Inc.
- Distributor cap locating tab. This tab assures proper location of the cap onto the distributor housing.
- Distributor cap holddown. The distributor cap must be securely attached to the distributor housing to prevent contamination and to assure its location.
- Dirt and water in the cap. These contaminants will require additional voltage in order to fire the spark plug. If available voltage is not enough to overcome this resistance then no spark will occur at the spark plug.
- Center carbon insert. All of the high voltage coming through the coil on its way to the spark plug must pass through this insert. Any additional resistance caused by wear or contamination can cause the engine not to start or to misfire.
- Tower inserts. The inserts are made from aluminum or bass so it is possible for them to oxidize. Aluminum oxide is an abrasive that can cause excessive damage to the distributor. If the insert is made from brass then the oxidation will appear green in color.
- Cracks. If any cracks are present on the distributor cap then replacement of the part is required.
- Carbon tracking. Carbon tracking indicates that the high-voltage of electricity has found a low-resistance conductive path over or through the plastic. The result is a cylinder that fires at the wrong time, or a misfire.
Also check for:
- Physical or electrical damage is easily recognizable.
- Electrical damage from high voltage can include corroded or burned metal terminals and carbon tracking inside distributor caps.
Things to look for when inspecting a distributor cap.
- If the distributor cap has a mild buildup of dirt or corrosion, it should be cleaned. If it cannot be cleaned up, it should be replaced. Small round brushes are available to clean cap terminals.
- Wipe the cap and with a clean shop towel, but avoid cleaning these components in solvent or blowing them off with compressed air, which may contain moisture. Cleaning these components with solvent or compressed air may result in high-voltage leaks.
- Check the distributor cap and housing vents. Make sure they are not blocked or clogged. If they are, the internal ignition module will overheat. It is good practice to check these vents whenever a module is replaced.