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Š Goodheart-Willcox Co., Inc.


 Changes battery voltage to a very high voltage  Sends the high voltage to the spark plugs

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Basic Ignition System Battery voltage is stepped up to about 15,000 volts to fire the spark plug

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Ignition Systems Overview  Ignition System with Coil

To Contact Points

Battery

Ignition Switch

By-Pass Circuit

Ballast Resistor

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Secondary Windings

Primary Windings Coil


 Fed to the ignition system by the battery and alternator  Components:  ignition switch  bypass and resistance circuits

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Ignition Switch  Key-operated switch  Supplies power to the coil primary winding  directly  through bypass and resistance circuits

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 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

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Primary Circuit Includes all the parts operating at battery voltage

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Secondary Circuit Includes all the parts carrying coil output voltage

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Ignition System

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 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

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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

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Ignition Coil

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Ignition Systems Overview  Conventional Coil

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Ignition Systems Overview  GM Ignition Coil—Out of Distributor Cap

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Ignition Systems Overview  Electronic Coil

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Ignition Systems Overview  Ford Coil Ignition Module

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Ignition Systems Overview  GM Coil Ignition Module

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Ignition Systems Overview  GM 4.2 Liter Inline 6-Cylinder Engine—Individual Coil Packs Coil Packs

Camshaft Crankshaft Sensors

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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 © Goodheart-Willcox Co., Inc.


Primary Dwell Period When current flows through the coil primary windings, magnetic field builds

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Dwell Ending—Ignition When current flow stops, magnetic field collapses across secondary windings

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Point Dwell (Cam Angle) Amount of time, in degrees of distributor rotation, that the points remain closed between each opening

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Pickup Coil Operation

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Ignition Control Module A. Remote-mounted B. Side of the distributor C. Inside the distributor

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Operation—Dwell

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Operation—Ignition

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Small gear on the cam drives the distributor at onehalf engine rpm

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Distributor Functions  Controls on/off cycle of coil primary

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Distributor Cap and Rotor Rotating rotor feeds high voltage to each spark plug wire

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Ignition Systems Overview  Mallory Distributor Cut-away

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Coil Pack

Several coils in one assembly

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Wasted-Spark Ignition Coil One plug fires on compression, the other on the exhaust stroke

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 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

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Secondary Wires Carbon-impregnated strands prevent radio interference

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 Use high voltage to ignite the fuel mixture  4000 to 28,000 volts make current jump the gap

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Seat and Thread Design 14 mm is the most common size

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Spark Plugs A. Non-resistor B. Resistor

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Spark Plug Heat Range

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Ignition Systems Overview  Spark Plug Components Connector to Plug Wire Ceramic Insulator Electrode

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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

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 Spark timing  How early or late the spark plugs fire in relation to piston position  Changes with speed, load, and temperature

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Timing Advance  Plugs fire earlier, before top dead center (BTDC)  Gives combustion enough time to develop pressure on the power stroke

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

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Advance Mechanisms

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Centrifugal Advance

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Vacuum Advance

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Electronic Spark Advance

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Operation

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Direct Ignition System Four coils are needed for a four-cylinder engine

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Distributor Ignition Firing Orders

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Normal Used Plug

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Oil Fouled Plug

Worn rings, scored cylinder, leaking valve seals Š Goodheart-Willcox Co., Inc.


Ash-Fouled Plug

Poor fuel or oil entering cylinder Š Goodheart-Willcox Co., Inc.


Carbon-Fouled Plug

Slow driving, heat range too cold, weak ignition or rich mixture Š Goodheart-Willcox Co., Inc.


Preignition Damage

Advanced timing, low octane fuel, heat range too hot Š Goodheart-Willcox Co., Inc.


Normal Erosion

Old plug with prolonged use Š Goodheart-Willcox Co., Inc.


Gapping Spark Plugs Bend side electrode

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 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

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Resistance Test 2,000 -12,000 ohms per foot  50,000 ohms overall

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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

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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

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35 Ignition System I