Chapter 26 Ignition Systems

Ignition Systems Part of the computerized engine control system Three basic types Distributor-based Distributorless Direct ignition

Purposes of the Ignition System It must generate spark with enough heat to ignite the air/fuel mixture It must maintain the spark long enough to allow for complete combustion It must deliver the spark so combustion can begin at the precise time

Basic Circuitry - Primary Battery Ignition switch Ballast resistor (older systems) Ignition coil primary winding Triggering device Switching device or control module

Basic Circuitry - Secondary Ignition coil secondary winding Distributor cap and rotor (DI systems) High-voltage cables Spark plugs

Primary Circuit Operation Ignition switch on Current flows into primary coil winding A primary switching device stops current flow through the coil This causes the magnetic field to collapse

Secondary Circuit Components Ignition coil secondary winding Distributor cap and rotor (DI systems) Spark plug cables (some systems) Spark plugs

DI Secondary Circuit

Secondary Circuit Operation Collapse of the magnetic field in the primary induces high voltage into the coil secondary This voltage is used to establish a complete circuit so current can flow The excess energy is used to maintain the current flow across the spark plug gap

Knowledge Check Which of the following is NOT part of the primary circuit? A. Ignition switch B. Primary coil winding C. Spark plug D. Switching device C – Spark plug

EI Systems May have a single coil for each cylinder or two cylinders may share a coil The ignition module controls firing order and spark timing Additional energy is released as current flow This allows higher firing current and longer firing times, 1.5 ms compared to DI’s 1 ms

Coil at Plug Secondary Circuit

DIS Secondary Circuit

Ignition Coils Coils are pulse transformers Output dependant upon the number of windings and current flow CEMF increases time to become fully saturated Dwell is the period of current flow

Ignition Coils (Cont.) Typical coil requires 2-6 ms to be saturated Dwell period and primary current are controlled

Secondary Voltage Typical voltage requirement to jump the plug gap is 10,000 volts Most coils have at least 25,000 volts available – called secondary reserve voltage Reserve necessary to compensate for high cylinder pressures

Spark Jumping the Gap

Spark Plugs Provides the air gap Resistor reduces RFI Standard plug electrodes are copper Platinum and iridium electrodes extend plug life

Platinum tipped spark plug

Spark Plug Reach Reach is critical for proper gap placement

Heat Range Heat must be dissipated quickly Heat travels from the electrode through the insulator to the cylinder head

Spark Plug Gaps Correct gap is necessary for proper operation Too wide can cause misfiring Too narrow can cause fouling and misfires

Electrodes May be made of copper, platinum, iridium, or yttrium Various styles of positive and ground electrodes in use

Ignition Cables Carry high voltage to spark plugs Carbon fiber core acts as a resistor Reduces RFI and increases firing voltage Reduces plug wear by reducing current

Knowledge Check Which is not a common spark plug electrode material? A. Copper B. Yttrium C. Nickel D. Platinum C – Nickel

Triggering and Switching Devices A triggering device monitors crankshaft position

Triggering and Switching Devices (Cont.) A switching device controls current flow through the coil primary winding Electronic switching components are part of an ignition control module or the PCM

Engine Position Sensors Magnetic Pulse Generator Consists of a reluctor and pickup coil Metal Detection Sensor The electromagnet is in the pickup coil Hall-effect Sensor Produces a square wave signal Is most commonly used Magnetoresistive Sensor Looks like a magnetic sensor but outputs a signal like a Hall-effect Photoelectric Sensor Uses an LED and moving slotted disc

DI System Operation The camshaft drives the distributor at one-half crankshaft speed The position sensor triggers the switching device The coil is triggered by the switching device

Distributor May contain pick up assembly, ignition module, and coil Rotor sits on top of distributor shaft and spins inside of distributor cap

Electronic Ignition Systems No moving parts Cylinders individually controlled Flexible mounting locations Less radio frequency interference No timing adjustments More time for coil saturation

Double-Ended Coil or Waste Spark Systems One coil fires two plugs These are the companion cylinders One plug fires positive to negative The other fires negative to positive

Coil-Per-Cylinder Ignition Coil-on-plug and coil-near-plug Allows for more time between firings and increased saturation time A single coil failure affects only one cylinder COP require adaptors or plug wires to connect an ignition scope

Twin Spark Plug Systems One plug on intake side of combustion chamber and one on exhaust side Results in cleaner combustion

EI System Operation Biggest differences are in number of coils and the use of CKT and CMP sensors Layout and operation of the sensors are designed to provide fast engine starts and synchronization of the fuel and ignition systems

Hall-Effect Sensors

Magnetic Pulse Generators

Knowledge Check Technician A says a waste-spark system uses one coil per plug. Technician B says a waste-spark system fires one plug positive to negative and the other plug negative to positive. Who is correct? Technician B

Misfire Detection The CKP identifies which cylinder Detected by variation in crank speed PCM uses wheel speed data to determine if crank speed variation is from rough road conditions or misfire

Basic Timing The PCM controls timing and is not adjustable Timing is fixed during cranking Once a certain engine speed is reached, the PCM adjusts timing Timing inputs include RPM, load, throttle position, and coolant temperature

Timing Retard and Advance Timing controlled by ignition module Older systems used mechanical and vacuum systems

Timing Corrections Temperature Engine Knock Stabilizing Idle Advanced with low coolant temperature Engine Knock Timing retarded when knock is detected Stabilizing Idle Used if desired idle speed is not correct

Timing Corrections (Cont.) EGR Advanced when EGR is opened Transition Correction During rapid acceleration/decelerations Torque Control To smooth automatic transmission shifting Traction Control Reduces engine torque by retarding timing