|
Ignition System
The engine in a vehicle needs three things to run: fuel, air, and spark. Fuel System section presents how the engine receives fuel and air, now it is time for the spark. The ignition system on vehicles has changed over the years, but its purpose has been the same – to ignite the fuel-air mixture. The ignition converts chemical energy of the fuel into wanted mechanical energy of motion and wasted thermal energy. This section gives you the knowledge to identify and perform basic maintenance procedures on a vehicle’s ignition system.
Purpose of the Ignition System
As mentioned earlier, fuel, air, and spark must all be present for the engine to run. The purpose of the ignition system is to:
- Step up voltage.
- Ignite the fuel-air mixture efficiently and in a timely matter.
Step Up Voltage
One of the purposes of the ignition system is to step up voltage. Basic electrical principles were presented in Chapter 7, Electrical System. You know now that automotive batteries have a surface voltage of about 12 volts DC. This is sufficient for running accessories such as lights and radios, but not powerful enough to ignite the air-fuel mixture within the combustion chamber. Common voltages at the spark plug can range from about 10,000 to 50,000 volts. These high voltages are created with a coil, a step up transformer.
Ignition
Automotive engines are considered four-stroke engines (intake, compression, power, and exhaust). To get to the stroke that is wanted, the power stroke (that’s the one that gives the vehicle power to move), the engine must cycle through the other necessary strokes. In addition to this, most automotive engines have 4 to 8 pistons working together to provide the mechanical energy. Not only does the ignition system have to ignite the fuel-air mixture, it also needs to ignite it at the correct time. Some of the ignition system components carry low voltage (12 volts) while others support high voltages (10,000 to 50,000 volts). The ignition system is designed to monitor and control the ignition to make the vehicle run smoothly.
Trouble Guide
Engine Will Not Start (but does rotate)
- Moisture on ignition system components
- Worn or incorrectly gapped spark plugs
- Faulty ignition module or coil
- Cracked, burned, or corroded distributor cap or rotor
Generations of the Ignition System
Over the years automotive manufacturers have come a long way in making the “power” (ignition) stroke more efficient. This has been done by advancements in technology. The purpose over the years has been the same: to increase the voltage that induces a spark. Modern technology has made the power stroke more reliable and efficient. It should be noted that the following dates of the ignition generations are approximated. Depending on the automotive manufacturer, the implementation time of the ignition system generation may vary. The generations of the ignition system are commonly divided into the following eras:
- Conventional Ignition System
- Electronic Ignition System
- Distributorless Ignition System
Conventional Ignition System
The conventional ignition system was common in vehicles from about 1920 to the mid 1970s. This system is sometimes considered a mechanical type ignition system. Tune-ups during this age were frequent – sometimes every 5,000 to 10,000 miles. Common components in the conventional ignition include the battery, ignition coil, condenser, contact points, distributor cap, distributor rotor, spark plug wires, and spark plugs.
Electronic Ignition System
The electronic ignition system was common in vehicles from about 1975 to the early 1990s. Tune-ups during this age were required about every 25,000 miles. Common components in the electronic ignition system include the battery, ignition coil, ignition module, distributor cap, distributor rotor, spark plug wires, and spark plugs. The main advantage over the conventional ignition is the elimination of the contact points that physically rub on the distributor shaft. This elimination decreased the number of components that needed servicing. The ignition module in electronic ignition systems controls the spark.
Distributorless Ignition System
The distributorless ignition system was actually introduced in the mid 1980s, but really became popular in the early 1990s. Some manufacturers call this a direct ignition system. Tune-up intervals on the distributorless ignition systems vary, but some manufacturer’s boast up to 100,000 miles. Common components in the distributorless ignition system include the battery, individual ignition coils, electronic control module, spark plug wires, spark plugs, crankshaft sensor, and camshaft sensor. The advantages over the electronic ignition are the elimination of a mechanical distributor, increased voltage at the spark plug, better timed spark, and a more efficient running engine.
Ignition System Components
Changing technology has made major advancements in many parts of the ignition system. Over time some components were eliminated, others were added, while others stayed pretty much the same. The following is a list of the most common components on modern day vehicles:
- Battery
- Ignition Coil or Coil Packs
- Ignition Module
- Distributor Cap and Rotor
- Spark Plug Wires
- Spark Plugs
- Crankshaft and Camshaft Sensors
Battery
The battery, used in all three ignition generations, is a critical component in many systems: electrical, starting, charging, and the ignition. Electrical energy must be present to ignite the air-fuel mixture. The problem is that a 12-volt battery does not have enough push (electrical pressure) to create the spark that is necessary in the combustion chamber, but it is the starting point of power.
Ignition Coil
The ignition coil, used on all three generations, steps up the low voltage to the high voltage needed to ignite the air-fuel mixture. The conventional and electronic generations usually had one coil, while the distributorless generation has coil packs – a series of coils to induce voltage for each individual cylinder.
Ignition Module
The ignition module, used on electronic and distributorless ignition systems, is basically a switch that turns the low voltage from the battery on and off to the ignition coil(s). It is a transistor that is timed and controlled by an on-board computer. In conventional ignition systems, contact points controlled system spark mechanically.
Distributor Cap and Rotor
The distributor cap and rotor, used on conventional and electronic ignition systems, distributes or sends high voltage to each spark plug. The rotor rotates inside the cap, connecting and sending high voltage to one terminal at a time.
Trouble Guide
Engine Misses
- Faulty spark plug wires
- Worn spark plugs
- Worn distributor cap or rotor
Spark Plug Wires
Spark plug wires are used on all generations of electrical systems. On the conventional and electronic ignition systems, spark plug wires connect the distributor to the spark plugs at each cylinder. In the distributorless ignition system, the spark plug wires connect the coil packs to the spark plugs. The spark plug wires carry high voltage electricity.
Tech Tip
Changing Spark Plug Wires
Changing the spark plug wires is relatively easy. A couple of tips should be taken into account. Engines have certain firing orders that cannot be mixed up. Remove and replace only one wire at a time to avoid mixing up the wires. It is also a good practice to use dielectric grease in the boot end of each spark plug wire to inhibit corrosion.
Spark Plugs
The spark plug, used in all generations of ignition systems, completes the high voltage circuit. Voltage at the spark plug needs to be great enough to arc across a gap thus creating a spark. This spark is what ignites the air-fuel mixture. The center electrode on the spark plug is commonly made of copper or platinum. The gap between the center electrode and the grounded electrode is usually between 0.020 to 0.080 of an inch. Most engines have one spark plug per cylinder.
Tech Tip
Changing Spark Plugs
When changing spark plugs, it is recommended to use anti-seize compound on the threads. This prevents seizing that can result from the reaction when different metals come in contact with one another – especially important on vehicles with aluminum heads. This also allows easier removal of the spark plugs during the next service.
Crankshaft and Camshaft Sensors
The crankshaft and camshaft sensors are used on distributorless ignition systems. They keep track of piston and valve positions in the engine to efficiently time the spark.
Summary
The ignition system is designed to ignite the air-fuel mixture in the combustion chamber. Ignition systems have gone through three stages: conventional, electronic, and distributorless. Even though the ignition system may seem complex with computers, ignition modules, and sensors, there are things that the do-it-yourselfer can do to maintain and tune-up the engine to make it run smoothly for thousands of miles.
Top of Page
|
