Distributors and Ignition
A distributor routes high-voltage current from the ignition coil to the correct spark plug at the correct moment. It is found on older engines; modern engines use coil-on-plug systems instead, with no moving distributor cap.
What it does
A rotor arm turning inside the distributor cap passes high-tension current to each plug lead in firing order. Timing is set by the distributor’s position relative to the camshaft drive.
Signs a distributor is failing
- Misfire under load or at higher revs
- Difficult starting, especially in damp weather
- Rough idle or backfiring
- Visible tracking marks or carbon lines inside the cap
When to replace them
Caps and rotor arms are wear items on distributor engines, commonly replaced at major service intervals along with leads and plugs.
What to confirm before ordering
Have these ready and the counter can usually confirm the part in under a minute.
- Engine code and the number of cylinders
- Whether cap, rotor arm or the complete distributor is required
- Lead set type and length
- Whether the ignition timing will need resetting after fitting
Distributors and Ignition by vehicle
Pick your vehicle for the years and engines covered, and what is specific to that application.
Distributors and Ignition questions
Why does my car misfire in the rain?
Moisture on a cracked distributor cap or perished leads lets high-tension current track to earth instead of reaching the plug. It is one of the clearest signs the cap and leads are due.
Should the cap, rotor and leads be replaced together?
Yes. They form the high-tension circuit and age together. Replacing one and leaving the others usually means returning to the job shortly afterwards.