Distributor Caps: The Plastic Lid Over the Distributor

The distributor cap is the plastic cover over the distributor, with contacts inside that the rotor arm sweeps past to route high-voltage spark to each cylinder. It’s a wear item on engines with mechanical distributor ignition (mostly pre-2000 cars).

Failure modes

Internal cracking — the plastic cracks from heat and age, eventually carbon-tracking inside the cap. Spark "leaks" along the crack rather than jumping to the right contact. Symptoms: misfire, especially in damp weather; intermittent rough running; sometimes visible green-blue marks inside the cap when removed.

Contact erosion — the contacts inside the cap erode where the rotor brushes them. Eventually the gap to the rotor becomes too large for reliable spark transfer. Symptoms: hard starting, weak spark, gradual power loss.

Replacement

Always replace the cap and the rotor arm together. Replacement is straightforward — the cap is held by clips or screws, lifts off the distributor housing.

Brand

Bosch, NGK, Beru, Marelli cover OE-equivalent caps. Match by engine code and ignition system.

Find distributor caps for your engine on the Distributor Caps collection.