On older engines, distributors are used instead of ignition coils. 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.
Signs of a Faulty Distributor Cap and Rotor
A failing distributor cap may lead to misfires and other issues with drivability. Below are the top 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 run.
Sometimes the problem starts gradually where you will be able to start the vehicle after a couple of tries. If the distributor cap is the cause the problem is likely to get worse to a point where you cannot start the vehicle at all.
See Also: What Does a Bad Starter Sound Like?
2) Engine Noises
The distributor is a rotating component. If you start hearing high pitched squealing sounds after you start your car (which will likely sound different than a loose serpentine belt), 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.
The process for OBD1 diagnostics are a little different for each vehicle. Vehicles with OBD1 should have a small diagnostic box under the hood that allows you to connect a jumper wire between two pins to put the vehicle in diagnostic mode. See your vehicle’s manual or check an online forum for your specific vehicle to learn how to use your vehicle’s diagnostic box.
4) Shaking
Intense shaking may occur in your vehicle when you start it up, particularly while idling. This shaking is likely the engine misfiring, and a sign that you have engine problems. You may feel the vibrations through the seats because they’re so intense and the engine will not run smoothly.
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.
How Does a Distributor Work?
A distributor is a rotating component consisting of a rotor and a distributor cap. The distributor is powered by the vehicle’s electrical system. Inside the distributor cap there are small metal tabs. As the rotor spins, it completes the circuit with each tab in a circle.
The spark plug wires are then attached to the distributor cap in proper firing order, allowing each spark plug to fire in the correct order.
Distributor Cap and Rotor Replacement Cost
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When you need to replace your distributor cap and rotor because they have gone bad, you can expect to pay anywhere from $250 to $500 for the job. This total includes both parts and labor costs together.
In most cases, expect to pay somewhere between $100 and $200 for parts (distributor rotor and distributor cap) and another $150 to $300 in labor. As you can see, this isn’t too expensive of a job compared to others.
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 taught in high schools, replacing a distributor cap was likely one of the first things you learned how to do. But since modern ignition systems have no distributor, 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.
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An internal igniter broke and I installed an external igniter to a distributor for my Toyota Corolla, however, whenever it’s not on the engine there is spark on the plugs, I try to put the distributor on the car, the spark cuts. What could be a problem ?
How are you testing spark outside the car?
Thanks for the info
Thanks for the info…jus talked to the tranny experts who riled out my teanny needing work… and it was only one culprit left😆…everything else is redone and in tact. We redid it all jus to go bacc to the distributor🙄…we have the HEI cap and rotor already but didn’t think to replace the distributor itself…had a lil stutter or stall but was burning rubber and not overheating or leakn anything…😚 -ms. 72 olds
I have 71 VW and had starting problem engine shaking until I read this article and checked the distributor cap and rotor sure enough needed replacement changed new ht leads, cap, rotor the car starts first pop now thanks
Glad to hear we helped you out!