5 Symptoms of a Bad Distributor Cap
Older engines use a distributor instead of an ignition coil. The distributor cap transfers power to the spark plugs through a set of spark plug wires. This entire process occurs every time the engine’s cylinders need a spark to ignite the air-fuel mixture in the cylinders for combustion.
The distributor is a rotating part that consists of a rotor and a distributor cap. The distributor is powered by the vehicle’s electrical system. There are small metal tabs on the inside of the distributor cap. As the rotor spins, each tab completes a circuit that circles around.
The spark plug wires are then connected to the distributor cap in the correct firing order to ensure that each spark plug fires in the correct order.
Signs of a Bad Distributor Cap and Rotor
A bad distributor cap can cause misfires and other driving problems. Below are the main symptoms of a bad distributor cap and rotor:
1) Unable to start vehicle (Vehicle starting problems)
To start your car, you need a properly working distributor cap and rotor. Without an electrical spark in the combustion chamber, the engine will not run.
In some cases, the problem may develop gradually and you may not be able to start your vehicle after several tries. If the distributor cap is to blame, the problem may get worse and you may not be able to start your vehicle at all.
2) Engine noises (V-belt squeaking)
The distributor is a rotating part. If you hear a high-pitched squealing noise after starting the car (probably a different sound than a loose belt), your distributor cap may be very dirty and caked with grease and other debris.
If you hear popping, knocking, or clicking noises, your cap or rotor is faulty. Don’t tolerate these noises any longer than necessary.
3) Check the engine light
Since a faulty distributor cap and rotor affect the combustion process in your engine, you can definitely expect the check engine light to come on. The engine control unit can detect whenever improper combustion occurs in the cylinders. When this is enabled, the check engine light in the instrument cluster will come on. The warning light alone is not enough to indicate that the distributor cap and rotor are bad.
The problem is, if your vehicle has a distributor cap, it was probably manufactured before 1996 when the OBD2 protocol was introduced. So, simply scanning the codes with a code reader won’t do the trick.
The process of OBD1 diagnostics varies slightly from vehicle to vehicle. Vehicles with OBD1 have a small diagnostic box under the hood that allows you to connect a jumper cable between two pins to put the vehicle into diagnostic mode. For instructions on how to use your vehicle’s diagnostic box, consult your vehicle’s owner’s manual or visit the online forums for your particular vehicle.
4) Shaking
Your vehicle may shake violently when starting, especially when idling. This shaking is most likely due to an engine misfire and indicates an engine problem. The strong seat transmits the vibration and the engine does not start smoothly.
This is usually one of the signs that indicates a bad distributor cap, but it may also indicate other problems.
5) Engine stall
A bad distributor cap can cause your engine to stall. The spinning distributor rotor needs to generate voltage to keep the engine running.
If the rotor isn’t spinning properly, your engine will lose power and stall if you continue driving. The longer you leave this, the worse it will get.