Chapter 8: The Electrical System

Chapter 8: The Electrical System
    Chapter 8: The Electrical System

    Chapter 8: The Electrical System


    This chapter is about the electrical system of the vehicle. The main parts of the electrical system are the battery, alternator, and ignition system. The battery is the power source of the whole vehicle. The alternator is a re-charging device which is used to maintain the charge of the battery. The ignition system is used to ignite the fuel at the correct time during the Otto cycle of events (review Chapter 5 for the Otto cycle of events). 

    The ignition in this lesson is not the same as the key ignition; it s about the ignition system that is used in the engine to ignite the air-fuel mixture in the combustion chamber. Prior to 1975, the ignition system consisted of the ignition coil, capacitor, contact breaker, distributor and spark plugs. The ignition coil converts low voltage electricity into high voltage. The high voltage electricity is sent to the distributor through the rotor, then it transmits out the distributor cap through plug wires to the spark plugs. The contact breaker or contact points complete and interrupt the circuit to the ignition coil on the low voltage side. The capacitor absorbs a voltage spike when the points open to avoid burning the contacts of the points.

    In a modern vehicle the ignition system consists of a crankshaft position sensor, which sends a signal to the PCM (powertrain control module or computer). The PCM interprets the signal and sends a signal to the ignition coils on each cylinder. Then the ignition coils fire through the spark plugs. Some vehicles will use one coil for two cylinders, and some have a separate coil for each cylinder. When one coil is used for two cylinders, the spark plugs for both cylinders fire at the same time, but one of the cylinders will be in the exhaust step of the Otto cycle, so it s kind of a waste spark (not used to ignite fuel).

    The ignition system works in conjunction with fuel injection (Chapter 7) so that the correct Otto Cycle of events occurs in the cylinders. The cylinders of internal combustion engines are numbered and the firing sequence occurs in a specific order. The firing order can vary by vehicle make and model. The engine size is also a factor. 

    For example, in an 8 cylinder Chevy engine the cylinders might be numbered 1, 3, 5, 7 on the driver s side (or left side of the engine from the driver s perspective), and 2, 4, 6, 8 on the passenger side. The firing order for this particular engine would be 1, 8, 4, 3, 6, 5, 7, 2. 

    Spark Plug Gap: 
    The purpose of the spark plug gap is to create an electric arc or spark of high heat to ignite the air-fuel mixture in the combustion chamber at the correct time. If the gap is too small then the spark is not hot enough to ignite the fuel. If the gap is too wide, then the voltage is not high enough to create a spark. Either condition can create an ignition misfire, causing poor performance and high emissions.

    to be Continued ....

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