The ignition system in your car ignites the fuel inside the engine's combustion chamber at the optimal time in the piston stroke to produce the most power while emitting the least amount of emissions as possible. There are many configurations of ignition systems but all operate on the same principle, create a low energy field and collapse it onto a high energy coil and that transfers the electrical energy into the secondary ignition system, i.e. coil wire, distributor cap and rotor (if equipped) plug wires and finally the spark plug.

This system is triggered by the primary ignition system, this system varies depending on manufacturer but all operate on the same principle, use some kind of low voltage trigger system i.e. crankshaft position sensor (CKP), camshaft position sensor (CAS). This low voltage system (1.5 to 3.0 volts) is amplified to 12 volts by using an ignition module (amplifier) and then transferred to the primary side of the ignition coil. The computer PCM (Powertrain control module) controls the engine ignition timing by advancing and retarding the primary trigger signal. In old cars a points, condenser and a vacuum advance unit performed this job.

This ignition coil is a pulse-type it consists, in part, of two coils of wire. These wires are wrapped around two iron cores. Because this is a step-up transformer, the secondary coil has far more turns of wire than the primary coil. The secondary coil has several thousand turns of thin wire, while the primary coil has just a few hundred raps. This allows 40,000 volts or more of voltage to be generated from battery voltage. This electrical signal is generated by the crankshaft position sensor (CKP), camshaft position sensor (CAS). The PCM calculates spark timing by using the computer system.

DIS Distributorless Ignition System

Some ignition systems have a coil for each spark plug. This is called Direct Ignition (DI) system; there are no plug wires in this system just individually controlled ignition coils. The amount of coils or spark plugs depends on the number of cylinders the engine is designed with.

Coil Over Spark Plug Style

The initial power supplied to the ignition system is generated from the battery. All vehicles use an alternator to recharge the battery during normal operation. A low battery can cause an engine not to start even if the engine is cranking over slowly. This is because the vehicle voltage has dropped below 12 volts. If any component of the ignition system is not functioning properly, it can cause an entire ignition system failure. Proper maintenance such as a tune up can help ensure that the vehicle's ignition system operates at peak performance. When an engine misfires under power it is typically caused by the ignition system. To troubleshoot the cause of the ignition system failure scan the PCM for trouble codes and repair as needed. Maintenance to the ignition system includes changing the spark plugs and distributor cap and spark plug wires if equipped. Changing the spark plugs and wires usually is a simple task that most people can perform themselves.

Distributor Cap and Rotor

The distributor cap and rotor are two essential pieces that distribute electrical current to the spark plugs. The distributor cap connects to the spark plugs directly using a spark plug wire. The number of plug wires connected depends on the amount of spark plugs that are in the engine. For example, an eight cylinder engine will have eight plug wires. The rotor is designed to spin inside of the distributor cap, just missing the terminals inside the cap. A worn or damaged rotor can cause your vehicle to run rough, or even stall completely. The rotor is rotating at the same speed as the camshaft which also happens to be 1/2 the speed of the crankshaft.

Distributor Cap and Rotor (appearance may vary)

How to Test an Ignition System

A problem occurs when the contacts inside the distributor cap can become dirty and worn. It is best to replace the distributor cap and rotor every tune up to ensure the contacts are clean to transmit power to each spark plug. The distributor cap and rotor generally have few problems other than worn connections that results in the cap needing to be replaced. There are numerous brands of distributor caps and rotors that are available. It is your decision to select the appropriate brand based on your individual wishes. However, when selecting the distributor cap and rotor it is best to select an OE (original equipment) replacement for proper performance and durability. If a misfiring problem has occurred and you cannot determine the cause of it, it is advisable to inspect the distributor cap and rotor for corrosion. Worn ignition components can cause the vehicle to misfire which leads to wasted fuel, rough running and stalling. Some early distributor ignition systems featured a point set and condenser. A solid state system was later adopted.

If further technical assistance is needed, ask our team of certified car repair technicians.

Related Car Repair Information

• Ignition Questions
• How to Scan for Engine Trouble Codes
• How to Tune Up a Car Engine
• How to Replace Spark Plugs
• How to Set Engine Ignition Timing
• Why Does an Engine Misfire and Run Rough?
• Why Does an Engine Stall?
• Engine Cranks Excessively Before Starting
• Engine Cranks But Wont Start
• Why Does an Engine Hesitate?
• Why Does an Engine Backfire?
• Engine has Low Power
• How Does a Car Computer Work?