(Updated on February 19, 2021)
When an engine starts running, it produces a great deal of voltage which enters the ignition coils. For older vehicles that have traditional distributors (not modern day ignition systems), this electricity is sent into an electrode of the distributor rotor.
This causes the rotor to rotate and transfer electrical power to separate electrodes which are positioned inside the distributor cap.
From there, the distributor cap transfers electricity to the spark plugs through a series of spark plug wires. This entire process happens each time the cylinders of the engine demand a spark to ignite the air and fuel mixture inside of them for combustion.
As you can see, the distributor cap and rotor are very important parts of the internal combustion process for older vehicles. You cannot afford to have a vehicle with a faulty distributor cap and rotor. If you do, you can expect a lot of problems with the overall functionality of your vehicle.
Signs of a Faulty Distributor Cap and Rotor
You will certainly recognize the symptoms of a bad distributor cap and rotor as they arise. Do not ignore these symptoms for too long or else you may find yourself stranded somewhere because your car won’t move. The only solution is to replace the distributor cap as soon as possible.
Below are the top 5 symptoms of a bad distributor cap and rotor.
1) Cannot Start Vehicle
You need a functional distributor cap and rotor to start the car. Without that electrical spark in the combustion chamber, the engine won’t start running.
You may only have difficulty starting your vehicle at first, but then it will get to a point where you cannot start the vehicle at all.
See Also: What Does a Bad Starter Sound Like?
2) Engine Noises
If you start hearing high pitched squealing sounds (different from a loose serpentine belt) after you start your car, then you may have a dirty distributor cap to the the point that it’s caked with grease and other build up.
If you hear a sputtering, tapping, or clicking noise, then it is either your cap or rotor that has gone bad. Don’t tolerate these noises for any longer than necessary.
3) Check Engine Light
Since a bad distributor cap and rotor affect the internal combustion process of the engine, you can definitely expect the Check Engine warning light to come on. The engine control unit can detect whenever there is improper combustion in the cylinders.
As soon as this is dedicated, the Check Engine light will turn on in your instrument cluster. The warning light alone won’t be enough to indicate that you have a bad distributor cap and rotor.
The problem is that if your vehicle has a distributor cap, there’s a good chance it was made prior to 1996 when the OBD2 protocol arrived so it’s not a simple matter of scanning for codes using your code reader.
Intense shaking may occur in your vehicle when you start it up or change gears. This shaking is a sign that you have engine problems for some reason. You’ll feel the vibrations through the seats because they’re so intense.
This is normally one of the signs of your distributor cap going bad but can signify other problems as well.
5) Engine Stalling
A faulty distributor cap can cause your engine to stall. Voltage must be produced by the spinning distributor rotor for the engine to keep running.
If the rotor does not rotate properly, the engine loses power and stalls out as you’re trying to drive. The longer you let this go on, the worse it will get.
Distributor Cap and Rotor Replacement Cost
When you need to replace your distributor cap and rotor because they have gone bad, you can expect to pay anywhere from $70 to $130 for the job. This total includes both parts and labor costs together.
In most cases, expect to pay somewhere between $30 and $60 for parts and another $40 to $70 in labor. As you can see, this isn’t too expensive of a job compared to others. But be prepared to pay some extra fees and taxes on top of the total estimated price.
Can I Replace the Distributor Cap and Rotor Myself?
For most people, this is a simple task and you’ll save yourself some money by doing so. Back when auto shop class was a thing in high schools, replacing a distributor cap was one of the first things you were taught. But since modern ignition systems are now distributor-less, the task has become a lost art.
Nonetheless, a good service manual will walk you through the process and you may even be able to find a YouTube video for the specific procedure to your vehicle. Just be sure to disconnect the car’s battery to avoid the possibility of zapping yourself.