A running engine sends a large amount of electricity through the ignition coils to the rotor, which turns inside the distributor. The rotor routes the energy in a specific through the spark plug wires ultimately to the engine’s cylinders in the correct firing order.

The distributor rotor and cap keep the distributor’s contents separate from the engine and keep the distributor’s working parts clean and tidy – while supporting the incredibly high volts of energy and delivering them to the appropriate spark plugs. The spark plugs utilize the spark from the distributor to ignite the fuel mixture, which is what keeps the engine running.

High voltage runs through this entire distributor system during the operation of your vehicle, but if there's an issue this voltage won’t get distributed to the correct spark plugs to ensure that your engine will run. Usually a faulty distributor rotor and cap will produce a few symptoms that alert the driver that service may be required.

1. Engine misfires

Engine misfires can occur for a number of reasons. Checking your distributor rotor and cap to see if they need to be replaced is one way to ensure that everything is in solid working order.

2. Car doesn’t start

When the distributor cap isn’t on tightly or is malfunctioning, the engine is unable to send the spark through the entire circuit required to move the cylinders – which ultimately make the car run.

3. Check Engine Light comes on

Your Check Engine light can mean a number of different things, but when you see this light on along with some of the other symptoms listed here, it’s time to call a professional to see what the code is from your car’s computer.

4. Excessive or unusual engine noises

Your vehicle may make some very strange noises if the distributor rotor and cap are malfunctioning – specifically because the cylinders will try to fire but fail. You might hear a tapping, clicking, or sputtering sound when the distributor rotor and cap are failing.

Any time you have routine service performed on your vehicle, ask that the ignition system be checked for defects or problems. If you experience any trouble starting your car get assistance from a qualified mobile automotive technician from YourMechanic.

This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Distributor Rotor and Cap and was authored by Valerie Johnston.


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