Conducting a visual inspection of the distributor is the best way to determine if it is faulty. There are also certain signs of a malfunctioning distributor. For example, if a car begins to sputter, the engine is not receiving enough power. A distributor transfers a high-voltage pulse to the cylinders to power the engine, so a faulty distributor is a common cause of loss of power.
When inspecting the distributor, look for build up or corrosion. The distributor must be free of debris and moisture to work properly, so cleaning the distributor is one way to diagnose and fix a faulty distributor. You also need to check the points of contact. Look for frayed wires, disconnected wires and burning patterns near the connection points.
The only other way to diagnose a faulty distributor is to determine whether or not the wires connected to the distributor are firing. To test this, disconnect one wire from the distributor and place the tip of a screwdriver on the wire. It is extremely important to do this while the engine is turned off. Only turn the engine on after you are no longer touching the wires and the screwdriver. If the wire fires, then it is working correctly. Repeat this test on each wire to isolate the problem.