Ignition Systems Overview CHAPTER 47 Ignition Systems Overview

Introduction (1 of 2) Ignition systems create a high-voltage spark and deliver it to the cylinders. The ignition system has primary and secondary circuits.

Introduction (2 of 2) Ignition system components include: Spark plugs, ignition coil, device for triggering the ignition coil The ignition system advances or retards the timing of the ignition spark.

Ignition Principles (1 of 20) Ignition system circuits deliver high voltage from the battery via the ignition coil to the cylinder.   

Ignition Principles (2 of 20) High voltage across the spark plug causes pressure. Original ignition system circuits were contact breaker point ignition systems.

Ignition Principles (3 of 20) Contact breaker systems were replaced with electronic ignition system, distributor types.  

Ignition Principles (4 of 20) The waste spark ignition system was the next advancement.    

Ignition Principles (5 of 20) In a direct ignition system, each cylinder has its own ignition coil.  

Ignition Principles (6 of 20) Induction coils convert low-voltage and high-current flow into high-voltage and low-current flow.

Ignition Principles (7 of 20) Ignition systems have primary and secondary circuits.  The low-voltage side is the primary circuit. The high-voltage side is the secondary circuit. Technicians must understand both circuits.

Ignition Principles (8 of 20) Faraday’s law explains induction coil operation. Induction coils increase battery voltage to bridge the gap across spark plug electrodes.

Ignition Principles (9 of 20) Faraday’s law: Relative movement between a conductor and magnetic field allows four ways for voltage to be induced in a conductor. Moving a magnet so the magnetic lines of force cut across a conductor

Ignition Principles (10 of 20) Faraday’s law (cont’d) Moving a conductor so it cuts across a stationary magnetic field Self-induction Mutual induction

Ignition Principles (11 of 20) Value of induced voltage depends on strength of magnetic field. Induced voltage becomes greater with: Stronger magnetic field, more turns of the coil, greater speed at which the lines of force are cut, higher current flow through the primary winding.

Ignition Principles (12 of 20) Primary current interruption disconnects the battery from the coil and stops current flow. Secondary voltage value is based on a ratio of number of turns of the primary winding to number of turns to the secondary winding.

Ignition Principles (13 of 20) Understanding required voltage versus available voltage Required voltage is the amount of voltage required to initially get current to jump the spark plug gap.

Ignition Principles (14 of 20) Available voltage is the maximum amount of voltage available to push the current to jump the spark plug gap.

Ignition Principles (15 of 20) Available voltage must always be higher than required voltage. Ignition systems are designed to have reserve voltage.

Ignition Principles (16 of 20) Available voltage, required voltage, reserve voltage, and misfire.

Ignition Principles (17 of 20) Spark timing is critical to engine operation. Spark plug timing varies according to: Air–fuel ratio, detected knock, engine speed, engine load, engine temperature, air temperature, transmission gear selected, throttle position

Ignition Principles (18 of 20) Spark timing may be advanced or retarded depending on engine revolutions. In the past, base spark timing was indexed to the number one cylinder.

Ignition Principles (19 of 20) Vehicles use electronically triggered ignition systems located on the engine block.  The timing components are fixed in position within the distributor (if used) or on the engine block and crankshaft or flywheel.

Ignition Principles (20 of 20) Older vehicles use mechanical advance systems. Vacuum advance units adjust  spark timing based on engine vacuum.

Standard Components of an Ignition System (1 of 20) Ignition systems include: Battery Ignition switch Ignition coil High-tension leads Spark plugs

Standard Components of an Ignition System (2 of 20) Automotive batteries are chemical-electrical devices. Batteries supply electrical energy to ignition circuit during start-up.

Standard Components of an Ignition System (3 of 20) Ignition switch disconnects electrical accessories from the battery. Ignition switch positions: Lock and off Accessory On/run Start/crank

Standard Components of an Ignition System (4 of 20) Key can only be removed from lock/off position. Accessory position allows power to run accessory features. On/run position activates warning lamps, accessories, ignition system. Start position activates the starter motor relay.

Standard Components of an Ignition System (5 of 20) Keys can be mechanical or an immobilizer system. A transmission shift interlock device requires a vehicle to be in park prior to key removal.

Standard Components of an Ignition System (6 of 20) Ignition coils are step-up transformers. Ignition coils amplify low battery voltage to required high voltage.

Standard Components of an Ignition System (7 of 20) Voltage is pushed through primary and secondary windings. Ignition coils contain thin enameled copper wire.

Standard Components of an Ignition System (8 of 20) Positive and negative terminals are connected to the primary winding. Secondary winding is connected to: Center terminal Primary winding/ground

Standard Components of an Ignition System (9 of 20) High-tension leads connect secondary ignition components together. Leads link: High-tension terminals Distributor cap Spark plugs

Standard Components of an Ignition System (10 of 20) High-tension leads have thick insulation and a carbon-impregnated linen or fiberglass core.

Standard Components of an Ignition System (11 of 20) Coil wires transmit high voltage from the ignition coil to the distributor cap. No coil wire in: Systems with wire mounted inside the distributor cap Distributorless systems

Standard Components of an Ignition System (12 of 20) Spark plug: Plated metal shell with ceramic insulator that has an electrode extending through its center

Standard Components of an Ignition System (13 of 20) Spark plugs have up to 4 side electrodes. Spark plugs are identified by: Thread size or diameter Reach or length of the thread Heat range or operating temperature

Standard Components of an Ignition System (14 of 20) Spark plug components: Ceramic insulator Electrode The metal case: Removes heat from insulator Passes heat to cylinder head Acts as a ground

Standard Components of an Ignition System (15 of 20) Spark plug heat range is determined by: Ribbing design Composition of insulator material Length of the insulator Spark plugs seal the combustion chamber.

Standard Components of an Ignition System (16 of 20) Spark plug is electrically connected to ignition system. Center electrode is hottest part of spark plug. Modern spark plugs: Last longer Are replaced, not refurbished

Standard Components of an Ignition System (17 of 20) Spark plug size = diameter of threads. 14-mm or 18-mm spark plug is used today. SAE and ISO have standards for spark plug: Length Hex size Thread diameter Thread pitch

Standard Components of an Ignition System (18 of 20) Spark plug reach = distance from the spark plug seat to end of the spark plug threads. Spark plug reach: Not too long Not too short

Standard Components of an Ignition System (19 of 20) Spark plug heat range: Between 746°F and 1460°F, or 400°C and 800°C Spark plug operating temperature = temp at sparking tip of spark plug inside a running engine.

Standard Components of an Ignition System (20 of 20) Longer heat path = more heat retention, higher running temperature. Spark plug heat range is affected by: Design profile Manufacturing material Engine operating conditions

Types of Ignition Systems (1 of 35) Ignition systems have evolved over the years. Main difference among systems: The way primary circuits are controlled to produce a secondary spark

Types of Ignition Systems (2 of 35) Contact breaker point ignition systems Contact breaker is a mechanically operated electrical switch. Contact points: Located in the distributor Opened by cam lobes

Types of Ignition Systems (3 of 35) Contact breaker point ignition systems (cont’d) Battery, ignition switch, ignition coil, contact breaker points, capacitor, distributor, connecting wires or leads

Types of Ignition Systems (4 of 35) Opening and closing contact breaker switches interrupts primary current, collapses magnetic field, and increases voltage value. Capacitor absorbs voltage surge across the contacts.

Types of Ignition Systems (5 of 35) Dwell angle = amount of time that contacts are closed. The setting of the contact breaker gap influences the dwell angle.

Types of Ignition Systems (6 of 35) A ballast resistor reduces voltage and current to the ignition coil.

Types of Ignition Systems (7 of 35) Ballast resistors provide correct voltage to the ignition system. Solid-state electronic ignition systems do not need a ballast resistor.

Types of Ignition Systems (8 of 35) Distributor ensures spark to the spark plugs in the correct sequence and at the correct time.

Types of Ignition Systems (9 of 35) Distributor.

Types of Ignition Systems (10 of 35) Distributor includes: Cap Rotor Switching device Shaft with cam lobes

Types of Ignition Systems (11 of 35) Distributor cap: Protects components inside Provides a connection point between the rotor and spark plug leads

Types of Ignition Systems (12 of 35) A rotor arm turns inside the distributor cap. High-tension leads are arranged according to place in the firing order. The distributor houses the mechanical and vacuum timing advance mechanisms.

Types of Ignition Systems (13 of 35) Centrifugal advance mechanism controls ignition timing in relation to engine speed. Upper or lower shafts turn to advance or retard ignition timing.

Types of Ignition Systems (14 of 35) Vacuum advance mechanism controls ignition advance in relation to engine load. Light load = advances timing Heavy load = retards timing

Types of Ignition Systems (15 of 35) Types of vacuum on which the vacuum advance operates: Ported Manifold Venturi

Types of Ignition Systems (16 of 35) Gasoline engines have valve timing and ignition timing. Valve timing = valve position in relation to piston stroke. Ignition timing = when the spark plug fires near the end of compression stroke.

Types of Ignition Systems (17 of 35) Electronic ignition systems: Eliminate contact breaker points Contain a power transistor Electronic ignition system components: Stationary Spinning

Types of Ignition Systems (18 of 35) Electronic ignition system triggering device: Magnetic-pulse generator Hall-effect sensor Optical sensor Triggering device sends signal to ignition module to begin ignition process.

Types of Ignition Systems (19 of 35) Ignition modules are used in almost every system. Ignition modules use triggering device information to control the primary circuit. In newer models, PCM controls ignition module functions.

Types of Ignition Systems (20 of 35) Induction-type systems generate AC signal. Systems have: Stator on the distributor body Rotor unit attached to distributor shaft

Types of Ignition Systems (21 of 35) Systems produce: Alternating current voltage Alternating current flow

Types of Ignition Systems (22 of 35) Internal module control circuit receives the trigger signal.

Types of Ignition Systems (23 of 35) The primary winding in the ignition coil: Is continuously turned on and off, causing secondary windings to generate high voltage used to create a spark at each compression stroke.

Types of Ignition Systems (24 of 35) Hall-effect sensors signal ECU to turn primary circuit on/off. Hall-effect voltage is created by deflection of electrons to one side of a conductor.

Types of Ignition Systems (25 of 35) Hall-effect generator is mounted on distributor base plate. Voltage turns on/off to control operation of ignition coil primary circuit.

Types of Ignition Systems (26 of 35) Optical-type sensors use: Light-emitting diode (LED) Phototransistor

Types of Ignition Systems (27 of 35) Phototransistors receive light beam from LED to make a voltage output signal. Control unit determines ignition timing.

Types of Ignition Systems (28 of 35) Distributorless-type systems have multiple ignition coils. PCM uses sensor data to know crankshaft and camshaft position. Distributorless ignition system main advantage: Elimination of mechanical parts

Types of Ignition Systems (29 of 35) Crankshaft and camshaft sensors: Calculate engine speed Determine engine position Sensors advance or retard spark plug firing.

Types of Ignition Systems (30 of 35) Crank sensor contains: Two Hall-effect switches Two concentric interrupter rings

Types of Ignition Systems (31 of 35) Waste spark ignition systems have: Event cylinder Waste cylinder Each set of cylinders enacts the same process. Timing is controlled by the PCM.

Types of Ignition Systems (32 of 35) Direct ignition systems Single ignition coil for each cylinder Each coil is directly connected to spark plug via spark plug boot.

Types of Ignition Systems (33 of 35) Spark timing for distributorless ignition systems is controlled by the PCM.

Types of Ignition Systems (34 of 35) PCM relies on: Mass airflow sensor Manifold absolute pressure sensor Throttle position sensor Cam and crank angle sensors Coolant temperature sensor

Types of Ignition Systems (35 of 35) Some systems include a knock sensor. Manufacturers may include circuitry to monitor detonation or pinging and misfires.

Diagnosis (1 of 14) First step is thorough visual inspection of the ignition system. If vehicle does not have OBDII system, inspect the spark. If vehicle has OBDII system, scan the PCM for related DTCs.

Diagnosis (2 of 14) Diagnostic tools Special spark plug socket Spark plug gapping tool High-tension insulated wire puller Spark tester Digital volt-ohmmeter Test light Oscilloscope

Diagnosis (3 of 14) Oscilloscopes evaluate ignition system condition. Oscilloscopes can test primary and secondary circuits.

Diagnosis (4 of 14) Parade pattern is a scope pattern showing all cylinders firing in sequence.

Diagnosis (5 of 14) Firing line = lines that indicate the voltage required to ionize spark plug gap. Spark plug ignition patterns stacked vertically = raster.

Diagnosis (6 of 14) Ignition system complaints: Nonstarting Hard starting Lack of power Misfiring Lack of engine responsiveness

Diagnosis (7 of 14) First perform visual inspection. Check high-tension leads; use a scan tool. Check spark plugs; perform spark test.

Diagnosis (8 of 14) Perform spark testing when: Engine will not start One or more cylinders are misfiring There are drivability problems

Diagnosis (9 of 14) Inspect the primary and secondary winding for: Cuts Abrasions Signs of arcing

Diagnosis (10 of 14) Critical to test ignition coil for proper operation Diagnose the pickup assembly. Test if vehicle will not start due to lack of spark. Identify vehicle’s pickup assembly style.

Diagnosis (11 of 14) Faulty spark plug wires lead to: Misfires High exhaust emissions Poor fuel economy Lack of power Multiple ways to test the spark plug wire

Diagnosis (12 of 14) Defective distributor cap or rotor: Prevents spark plug firing Causes weak spark Inspect distributor cap and rotor for: Engine misfire Lack of engine power Poor fuel economy High emissions

Diagnosis (13 of 14) Test crankshaft and camshaft position sensors. Defective crankshaft/camshaft can prevent engine start-up. Test ignition module. Defective ignition module causes engine trouble.

Diagnosis (14 of 14) Find manufacturer-determined voltage or resistance values for each electronic ignition system component.

Removing and Replacing Secondary Ignition Components (1 of 3) Secondary ignition components include: Spark plugs High-tension leads Coil boots

Removing and Replacing Secondary Ignition Components (2 of 3) Replace spark plugs at 30,000 to 50,000 miles. Replace high-performance spark plugs at 100,000 miles. Remove spark plugs per manufacturer directions.

Removing and Replacing Secondary Ignition Components (3 of 3) Periodic replacement for: Spark plug wires High-tension leads COP boots Recommended replacement is 100,000 miles.

Summary (1 of 25) Ignition systems have a primary (low-voltage) circuit to connect and disconnect the ignition coil and a secondary (high-voltage) circuit to send voltage from the battery to the spark plug. Common components of an ignition system are the spark plugs, high-tension leads, ignition coil, and ignition-coil triggering device.

Summary (2 of 25) Principles of an ignition system involve a circuit activating the ignition coil, which converts the battery’s low voltage to high voltage. The voltage then travels to the spark plug in each cylinder, igniting the air–fuel mixture and creating enough pressure to push down the pistons.

Summary (3 of 25) The original contact breaker ignition system was replaced with an electronic ignition system of the distributor type. Modern systems are direct ignition systems (or coil-on-plug), which have a dedicated coil for each cylinder.

Summary (4 of 25) The amount of available voltage should always be higher than the amount of required voltage. As ignition components age and become worn, required voltage increases and available voltage decreases.

Summary (5 of 25) Spark timing is affected by any of these factors: air–fuel ratio, detected knock, engine speed, engine load, engine temperature, and throttle position.

Summary (6 of 25) Spark timing must be correct in order to give the air–fuel mixture enough time to burn. Modern vehicles have electronically programmed spark timing via the PCM; older vehicles mechanically advance or retard the spark timing.

Summary (7 of 25) Common points on an ignition switch are the lock and off functions and the accessory, on/run, and start/crank positions. Automatic transmission vehicles may employ a transmission shift interlock device to ensure that the gear selector is in park before key removal can occur.

Summary (8 of 25) Standard ignition coils contain primary and secondary windings around a rod-shaped laminated iron core. The main difference among types of ignition systems is the method used to control the primary circuit to produce the secondary spark.

Summary (9 of 25) In the primary circuit, a magnetic field develops that is interrupted by the ignition triggering device, thus collapsing the field and returning stored energy to ignition coil terminals. Because the secondary winding has approximately 100 times as many turns as the primary winding, it can produce 100 times greater voltage.

Summary (10 of 25) Basic contact breaker point ignition systems are comprised of the battery, ignition switch, ignition coil, contact breaker points, capacitor, distributor, and appropriate voltage-connecting wires and leads. The purpose of the distributor is to transfer the spark to the spark plugs with the correct sequence and timing.

Summary (11 of 25) The distributor cap provides rotor and spark plug lead connection. The distributor controls ignition timing in relation to speed via a centrifugal advance mechanism and ignition timing in relation to vehicle load via a vacuum advance mechanism. Vehicles regulate voltage to the ignition system via a ballast resistor, which is inserted in the primary circuit and lowers the voltage.

Summary (12 of 25) Spark plugs all have at least one, and up to four, side electrodes, as well as an internal resistor to suppress voltage spikes and prevent radio frequency interference. Spark plugs are identified by thread size or diameter, reach or length of thread, and heat range or operating temperature.

Summary (13 of 25) Spark plug components include the metal case, insulator, terminal, side electrode, and center electrode.

Summary (14 of 25) To work effectively, spark plugs must have proper reach (distance from sealing area to end of spark plug threads) and proper heat range (operating temperature, generally 746°F to 1,460°F [400°C to 800°C]).

Summary (15 of 25) High-tension leads carry a high-voltage spark from the ignition coil to the distributor cap and on to the spark plugs. Engine timing can refer to valve timing or ignition timing.

Summary (16 of 25) How long the contacts are closed and current is flowing in a contact breaker system is determined by the dwell angle. Electronic ignition systems electronically trigger the primary circuit (rather than using a contact breaker). The triggering device of an electronic ignition system can be a magnetic pulse generator (pickup coil) or a Hall-effect switch.

Summary (17 of 25) Ignition modules process information from various sensors and then interrupt the signal to the primary winding of the ignition coil. Induction-type systems use a magnetic pulse generator with a stator and a reluctor attached to the distributor body and shaft, respectively.

Summary (18 of 25) Induction-type systems produce an alternating current voltage. The internal module control circuit receives the trigger signal. The reluctor teeth spin past the stator, turning on and off the primary winding and causing the secondary windings to generate a high-voltage spark at the end of each cylinder’s compression stroke.

Summary (19 of 25) Hall-effect systems use a potential difference, or voltage, which is used as a switch device. In a Hall-effect system, the magnetic field is alternately blocked and exposed by an interrupter ring. Some ignition systems use a phototransistor to receive light from an LED and transform it into a voltage output signal.

Summary (20 of 25) In distributorless ignition systems, the distributor is eliminated so crankshaft and camshaft position sensors help determine when to send a signal to the coil’s primary windings by monitoring which cylinder is approaching its power stroke. In a six-cylinder, waste spark engine, each set of two cylinders is paired with an ignition coil. The cylinders alternate between an event cylinder and a waste cylinder.

Summary (21 of 25) The PCM controls spark timing for distributorless ignition systems via information from the following sensors: mass airflow sensor, manifold absolute pressure sensor, throttle position sensor, cam and crank angle sensors, engine speed sensor, knock sensor, and coolant temperature sensor.

Summary (22 of 25) Special tools and equipment for ignition system diagnostics include the spark plug socket, spark plug gapping tool, high-tension wire puller, spark tester, test light, a digital multimeter, scan tool, and an oscilloscope. Oscilloscopes test the condition of the secondary circuit and can show if voltage to any of the cylinders is too high, too low, or nonexistent.

Summary (23 of 25) The first step in diagnosing ignition system issues is to conduct a visual inspection to look for loose connections, broken or corroded terminals, or any components that need replacing. Inspect the primary and secondary circuit wiring for cuts, abrasions, and signs of arcing.

Summary (24 of 25) Test the ignition coil for primary and secondary winding resistance. If the vehicle will not start, performing a spark test is a good step. Test to ensure that the spark plug wire, distributor cap and rotor, crankshaft and camshaft position sensors, and ignition modules are in proper working order.

Summary (25 of 25) Always follow manufacturer-recommended procedures for diagnosing each ignition system component. Spark plugs and spark plug wires will wear over time and require replacement; check the manufacturer’s recommendations for replacement schedules.

Credits Unless otherwise indicated, all photographs and illustrations are under copyright of Jones & Bartlett Learning.