Troubleshooting Common Distributor Cap Problems

When trying to track down the possible cause of your car's engine “missing,” you should look at the distributor cap as one of the possible problems. If your car or truck is not getting the right spark to its cylinders, its engine is not going to run as efficiently as it should. You might trace the problem to your spark plugs or to your spark plug wires. But, having checked these components and finding them to be working properly, you will have one option to look at: the distributor and its cap.

Removing Your Spark Plug Wires

The probable cause of a malfunctioning distributor is not usually hard to spot. Before checking the cap for problems, remove the spark plug wires that are connected from the spark plugs to your distributor. Before pulling these wires off the distributor cap, be sure to make a note of the order in which they are connected. If you connect them in the wrong order, your car engine will certainly miss, and probably it won't run at all. Secondly, use a spark plug wire removal tool. These wires have a carbon core that is fragile. If you break this core while pulling the wire, it will interrupt the flow of electricity to your spark plug, and your car won't run right.

Removing Your Distributor Cap and Rotor

To remove your distributor cap, pull off the clips that hold the cap in place on the distributor. You should find these clips near the upper edge of the distributor, where it meets the cap. These clips snap onto the cap. Once your clips are off, remove the cap and the rotor. The rotor rests on the distributor shaft, located in the center of the distributor. You should be able to simply slide the rotor up the shaft until it comes off. 

Checking Your Distributor for Problems

Examine the inside surfaces of the cap. Look for wear near the metal contacts, and in places where the rotor might have touched as it turned. Also, look for cracks in the plastic and for wear to the rotor. In the center of the cap, you'll find a spring loaded button. This is what makes the rotor turn inside the distributor. You should be able to easily turn it. If it binds up, this could be the root of your problem. If this is the case, you should replace both the cap and the rotor. Similarly, if you find excessive wear in the cap or on the rotor, replace these components.

Reconnecting Your Distributor and Rotor

To re-install your distributor and rotor, fit the rotor over the distributor shaft, and slide it to the bottom of the shaft. Replace the cap on top of the distributor, so that the clips line up with the clip flanges. Then, snap the clips in place. When re-attaching your spark plug wires, check the notes you made for the proper order in which you should snap them back into place on your distributor cap. With everything in place, start your car engine and check to be sure it is running smoothly.