35 Ignition System I

© Goodheart-Willcox Co., Inc.


Changes battery voltage to a very high voltage

Sends the high voltage to the spark plugs


Basic Ignition System

Battery voltage is stepped up to about 15,000 volts to fire

the spark plug


Ignition Systems Overview Ignition System with Coil

Battery

Ignition Switch

Coil

BallastResistor

By-Pass Circuit

To Contact Points

Primary Windings

Secondary Windings


Fed to the ignition system by the battery and alternator

Components: ignition switch bypass and resistance circuits


Ignition Switch

Key-operated switch Supplies power to the coil primary

winding directly through bypass and resistance circuits


Primary circuit operates on low voltage 12–15 volts

Secondary circuit high voltage section, 4000–30,000 volts includes wires and parts between the coil

output and spark plug ground


Primary Circuit

Includes all the parts operating at

battery voltage


Secondary Circuit

Includes all the parts carrying coil

output voltage


Ignition System


Step-up transformer Produces short bursts of high voltage to

start combustion High voltage jumps the rotor gap,

passes through the secondary wire, jumps the spark plug gap

4000-8000 volts on old systems 4000-30,000 volts on newer systems


Ignition Coil Windings Primary

several hundred turns of heavy wire wrapped around or near the secondary

Secondary several thousand turns of fine wire

located inside or near primary windings Iron core

concentrates magnetic field


Ignition Coil


Ignition Systems Overview

Conventional Coil



GM Ignition Coil—Out of Distributor Cap



Electronic Coil



Ford Coil Ignition Module



GM Coil Ignition Module



GM 4.2 Liter Inline 6-Cylinder Engine—Individual Coil Packs

Coil Packs

Camshaft Crankshaft Sensors


Coil Operation Current flows through primary winding Strong magnetic field is generated Iron core helps concentrate field When current is interrupted, magnetic

field collapses across the secondary winding

Up to 60,000 volts is induced


Primary Dwell PeriodWhen current flows through the coil

primary windings, magnetic field builds


Dwell Ending—IgnitionWhen current flow stops, magnetic field

collapses across secondary windings


Point Dwell(Cam Angle)

Amount of time, in degrees of distributor rotation, that the points remain closed

between each opening


Pickup Coil Operation


Ignition ControlModule

A. Remote-mountedB. Side of the distributorC. Inside the distributor


Operation—Dwell


Operation—Ignition


Small gear on the cam drives the

distributor at one-half engine rpm


Distributor Functions Controls on/off cycle of coil primary


Distributor Cap and Rotor

Rotating rotor feeds high voltage to each

spark plug wire


Ignition Systems Overview Mallory Distributor Cut-away


Coil Pack

Several coils in one assembly


Wasted-SparkIgnition Coil

One plug fires on compression, the

other on the exhaust stroke


Carry current produced by ignition coil Solid wires

wire conductor may cause radio interference Used in racing

Resistance wires carbon-impregnated strands and rayon braids about 10,000 ohms per foot prevent radio noise


Secondary WiresCarbon-impregnated strands prevent

radio interference


Use high voltage to ignite the fuel mixture

4000 to 28,000 volts make current jump the gap


Seat and Thread Design

14 mm is the most common size


Spark Plugs

A. Non-resistorB. Resistor


Spark Plug Heat Range


Ignition Systems Overview Spark Plug Components

Connector to Plug Wire

Ceramic Insulator

Electrode


Multiple Discharge Ignition

Fires the spark plugs more than once on each power stroke

Promotes complete burning of fuel charge

Often used on racing engines


Spark timing How early or late the spark plugs fire in

relation to piston position Changes with speed, load, and

temperature


Timing Advance

Plugs fire earlier, before top dead center (BTDC)

Gives combustion enough time to develop pressure on the power stroke


Timing Retard

Plugs fire later Used in low speed, high load conditions Prevents spark knock or ping


Advance Mechanisms


Centrifugal Advance


Vacuum Advance


Electronic Spark Advance


Operation


Direct Ignition SystemFour coils are needed for a

four-cylinder engine


Distributor Ignition Firing Orders


Normal Used Plug


Oil Fouled Plug

Worn rings, scored cylinder, leaking valve seals


Ash-Fouled Plug

Poor fuel or oil entering cylinder


Carbon-Fouled Plug

Slow driving, heat range too cold, weak ignition or rich mixture


Preignition Damage

Advanced timing, low octane fuel,heat range too hot


Normal Erosion

Old plug with prolonged use


Gapping Spark PlugsBend side electrode


Wire conductors become burned or broken cause misfire or dead cylinders

Insulation deteriorates sparks jump to ground or another wire causes misfire or dead cylinders


Resistance Test

2,000 -12,000 ohms per foot 50,000ohms overall


Insulation Test Check for sparks arcing through

insulation to ground or another wire Move test light or grounded screwdriver

along each wire If an arc jumps to probe, insulation has

broken down—replace wires


Wire Replacement

Replace one wire at a time, if possible If all wires are removed, use firing order

and cylinder numbers to route wires Use factory routing

35 Ignition System I

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