Distributor Cap

What is a Distributor Cap and where is it Located?

Before automotive manufacturers moved to using individual coils per cylinder, the distributor assembly was an important part of the ignition system. The distributor would tell the ignition coil at what moment when to fire and transfer the energy from the coil to a specific engine cylinder in order for engine ignition to occur. Older classic vehicles used breaker points and a condenser for this process (mechanical ignition system), whereas later models used electronic systems that relied on an ignition module and the engine’s computer for more precise timing (electronic ignition system). In modern automobiles, the distributor is no longer necessary as they are equipped with a distributorless ignition system, also referred to as a direct ignition system (DIS). In vehicles that do use a distributor assembly, it is located on top of the engine, either in front or in back of it depending upon the car or truck.

One of the many components of a distributor assembly is the distributor cap. Also referred to as a distributor cover, the cap is mounted to the top of the housing and fits over the distributor rotor, covering it. It also holds in place the wires that connect the individual cylinder points underneath the distributor cap to the spark plugs screwed into each engine cylinder. The distributor cap helps to transfer the electricity from the distributor rotor underneath the cap to the spark plug wire for each cylinder in order for the engine to start.

So, how does a distributor assembly work exactly? Basically, electricity from the battery is transferred to the ignition coil, and the distributor takes the high voltage output from the ignition coil and feeds it through the ignition wires to the spark plugs that are screwed into each engine cylinder in the order of the firing sequence. The distributor uses the rotation of the engine’s camshaft, which it connects to via the distributor shaft, to spin the distributor rotor, which connects directly to the ignition coil, close to (but not touching) the individual cylinder posts (or points) underneath the distributor cap. Each of the postd are connected via a spark plug wire – which connect to the top of the distributor cap via plug terminals - to the spark plug(s) inserted into each cylinder, and are arranged along with the wires according to the engine cylinders' correct firing order sequence. As the rotor spins within the distributor, electrical current is able to jump the gaps between the rotor arm and the individual posts due to the high voltage created by the ignition coil. The electrical current is then transferred from the rotor to the spark plug wire, and then to each spark plug attached to each engine cylinder according to the firing order, allowing for proper ignition spark at just the right time for the engine to start.

When is a Distributor Cap Replacement Needed?

While distributor caps are made of voltage-insulating materials in order to prevent them from being burned by electricity and consist of low-resistance terminals to maximize their conductivity, they are the most commonly serviced part of the distributor assembly besides the distributor rotor. Distributor caps wear out and should be inspected yearly for damage. Over time, the distributor cap can become brittle and crack. Cracks in the cap can allow moisture into the distributor assembly and cause misfire or no fire situations as well. In other cases, carbon build-up between the rotor and cap will lower the ignition coil’s ability to fire the spark plugs. The distributor cap’s electrical connections can also become worn over time, causing similar issues.

If your car or truck uses an ignition system that depends on an ignition distributor and the cap has failed, your engine will not be able to function properly, or at all, and thus your car won’t start when you turn the ignition key. Therefore, obtaining an ignition distributor cap replacement and getting it installed is imperative if you plan on driving your vehicle ever again.

Can I Replace a Distributor Cap Myself?

Replacing a distributor cap is a very simple task and usually only requires removing two or three screws.  Proper precaution to label each spark plug wire before removal will aid in a quick replacement as well.  When replacing a distributor cap, it is recommended to replace the rotor button as well. Since both parts require the same amount of work and receive the same amount of wear and tear, it’s a no brainer.

Need a Distributor Cap Replacement?

There are many components in a distributor assembly and when any one of them starts to go bad, it can cause your vehicle to run rough, idle poorly, stall, make popping noises, or hard start. If you have determined that the failed component happens to be the distributor cap, it’s essential that you obtain a replacement and install it immediately. At 1A Auto, you will find a large selection of aftermarket distributor caps for many makes and models, at great prices.

Shopping for an aftermarket distributor cap replacement is also incredibly easy at 1A Auto - we're here to help you select the right part for your vehicle! Call our customer service toll free at 888-844-3393 if you have any questions about our distributors, warranty, compatibility or to purchase, or you can buy online right here at 1aauto.com. If you are in need of a replacement distributor for your car, truck, SUV or van, then you have certainly come to the right place.