In order for your vehicle to start, and for the internal-combustion process to work, a spark must be present to ignite the fuel/air mixture that allows your engine to run -- hence the term "ignition." The battery supplies the necessary electrical current that allows the spark plugs to create the actual spark, but there's more to the process than that. The sparks must be sent to the individual engine cylinders in just the right sequence, and with exact timing, in order for the engine to operate properly. In new cars, that's achieved by means of a computerized ignition system. In older vehicles, the process is controlled by a mechanical system that involves, among other things, a distributor. This type of ignition system is sometimes referred to as a breaker-point ignition since it relies on a breaker device inside the distributor that utilizes mechanically controlled contact points to regulate and direct the flow of electrical current. Tuning up an older vehicle involves changing the spark plugs to ensure continuous and reliable delivery of spark to the engine, as well as other measures that pertain to the proper control of that process by means of the distributor. Whether you want to perform a tune-up yourself or you rely on a professional mechanic or tune-up shop to do it for you, it's helpful to have a basic understanding of how the system works. For demonstration purposes, we removed the parts that comprise the ignition system from a vehicle to display them and show how they all work together. The spark that will eventually ignite the vaporized fuel at the spark plug begins with an electrical charge originating from the vehicle's battery. When you turn the ignition key, 12-volt current flows from the battery to the ignition coil (figure A). The ignition coil transforms the low-voltage current to a much higher voltage -- possibly 30,000 volts or more. The amplified current then travels via the coil wire to the distributor (figure B), which -- true to its name -- distributes the current to several spark-plug wires. The number of spark-plug wires (figure C) that you have in your vehicle matches the number of cylinders in your engine. The voltage then is transferred, in rapidly cycling intervals controlled by the distributor, via the plug wires to each of the spark plugs. The spark that forms at the electrode end of the spark plug (figure D) is what causes the explosive reaction in the vaporized fuel inside each engine cylinder, causing the pistons to move up and down. This "controlled explosion," and the resulting motion of the pistons, is the source of power that is ultimately transferred into the motion of your vehicle. Any interruption to the flow of current in the ignition system will affect how the vehicle runs. Depending on the nature of the interruption, the vehicle may be difficult to start, may run rough or may not start at all. In order to see how the distributor operates, we disassembled our demonstration unit by removing the distributor cap (figure E) to expose the breaker points. The breaker points can be thought of as analogous to an electrical on/off switch. As the breaker (figure F) opens and closes, the contact points effectively connect and disconnect to regulate the flow of voltage through the system -- making certain that electricity arrives at the spark plug at exactly the right time and intensity. To accomplish this, the inside of the distributor assembly (figure G) is equipped with a rotating cam that has a number of lobes. (The number of lobes matches the number of spark plugs that the engine uses.) As the cam rotates, it causes the breaker to open and close. For a six-cylinder engine, the breaker will open and close six times with each complete rotation of the cam. The gap between the open points allows current to flow to a rotor, which sits atop the cam (figure H, right). The rotating rotor comes into contact, in succession, with each of terminals inside the distributor cap (figure H, left), thus directing the current to each of the spark-plug wires in sequence. The distributor is also equipped with an electrical condenser that regulates the amount of voltage to keep the points from burning out quickly. Without a regulator, the points might burn out every thousand miles or so. This is why it's advisable to replace the condenser at tune-up time along with the spark plugs and spark-plug wires.
RESOURCES :
The Complete Idiot's Guide to Trouble-Free Car Care
Author: Dan Ramsey
ISBN: 0028635833
Alpha Books
Auto Repair for Dummies
Author: Deanna Sclar
ISBN: 0764550896
Professional Tips and Techniques for Tune-Up and Electrical Service
Model: 1879110156
Author: Michael Bishop and Dennis Holmes
To order this title from Amazon.com, click here.
Do-It-Right Publishing
New Hall, CA 91322
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