Ignition Systems

The primary purpose of the ignition system in a spark ignition engine is to:

Provide fuel to the cylinders Ignite the air fuel mixture at the correct time Lubricate moving components Control exhaust emissions mechanically

In a basic ignition coil, electrical energy is stored in the:

Primary and secondary windings magnetic field Spark plug insulator Distributor cap terminals Battery plates only

The primary winding of an ignition coil is connected to:

Battery positive and a switching device such as points or an ignition module The spark plug centre electrode The alternator stator windings The starter solenoid S terminal

Coil on plug (COP) ignition systems differ from distributor systems because COP:

Uses a single coil and mechanical rotor Provides one coil for each cylinder mounted directly on the spark plug Eliminates the need for any electronic control Can only be used on carbureted engines

Correct ignition timing is important because it:

Ensures maximum cylinder pressure occurs at the correct point after top dead centre Prevents alternator overcharging Controls starter motor torque Eliminates the need for a cooling system

The secondary winding in an ignition coil typically produces:

Battery voltage only High voltage required to jump the spark plug gap Low voltage for sensors AC voltage for the charging system

The heat range of a spark plug refers to its ability to:

Produce a stronger spark Transfer heat from the firing end to the cylinder head Change ignition timing Increase fuel octane rating

An ignition misfire under load is often caused by:

Too small a spark plug gap Weak coil output or high resistance in secondary components Excessive fuel octane Low charging system voltage only

Distributorless ignition systems (DIS) often use a waste spark strategy where:

Only half the cylinders receive a spark Each coil fires two spark plugs simultaneously, one on compression and one on exhaust stroke Spark occurs only every second engine cycle Spark is provided only at idle speed

Crankshaft position sensors are used in modern ignition systems to:

Measure engine oil pressure Provide engine speed and position information for timing control Control alternator output Activate the starter drive

On a basic electronic ignition system, the module or control unit replaces the function of:

Spark plugs Mechanical breaker points Pistons and rings Battery terminals

A larger than specified spark plug gap will generally:

Reduce the voltage required to fire the plug Increase voltage demand and may cause misfire under load Have no effect on ignition performance Eliminate radio interference

Ignition coils are usually supplied with battery voltage during:

Key OFF only Cranking and run positions of the ignition switch Accessory position only Park position of the transmission

High tension leads (spark plug wires) should have:

Very low resistance and no insulation Proper insulation and controlled resistance to reduce radio interference Direct metal conductors with no insulation Resistance high enough to limit coil output

A coil on plug system often simplifies diagnosis because:

There are no coils to test Fewer components are shared between cylinders, so misfires can be related to individual coils or plugs The ignition system is purely mechanical It does not require any sensors

Ignition advance is required at higher engine speeds because:

The air fuel mixture burns faster at high RPM The air fuel mixture takes a relatively fixed time to burn, so the spark must occur earlier The alternator output decreases at high RPM Spark plugs fire multiple times per cycle

Knock sensors are used so that the engine control module can:

Advance ignition timing until detonation occurs Retard timing when knock is detected to protect the engine Turn the ignition system off during knock Control fuel pump operation only

An ignition system that uses a single coil and distributor is MOST likely found on:

Older engines with mechanical distribution of secondary voltage Modern coil on plug engines Diesel engines only Hybrid electric drives only

Carbon tracking inside a distributor cap can cause:

Improved spark distribution Cross firing and misfire between adjacent terminals Higher charging voltage Starter motor failure

The correct sequence in which high voltage is delivered to engine cylinders is called the:

Timing chain alignment Firing order Compression ratio Stroke sequence

When replacing spark plugs, a parts technician must verify:

Thread size, reach, heat range and design match application requirements Only that the plug physically fits the socket That all plugs are the hottest range available That gaps are all set as large as possible

Ignition system primary current is usually switched on and off by:

The alternator rotor An ignition module, PCM driver, or mechanical points The starter relay The horn switch

A misfire on one cylinder that moves when the coil on plug unit is swapped to another cylinder indicates:

Faulty injector on the original cylinder Faulty coil on plug unit Mechanical engine fault only Incorrect firing order

On an engine with a coil pack and plug wires, a misfire on paired cylinders may indicate:

Faulty alternator rectifier Faulty shared coil in a waste spark system Seized starter drive Low battery electrolyte level

Dwell time in an electronic ignition system refers to:

Time required for the starter to engage Length of time current flows in the coil primary winding before firing Duration of spark at the plug Time between oil changes

Ignition systems on modern engines are often integrated with:

The charging and starting modules only Engine management systems that also control fuel delivery and emissions The cooling fan motor only The power brake booster

When checking for ignition spark using a spark tester, it is important to:

Hold the plug wire with bare hands Use an approved tester and avoid creating open sparks near fuel vapours Disconnect all engine grounds Increase gap beyond the tester specification

Extended cranking with no start and strong fuel smell from the exhaust may indicate:

Ignition system fault with no spark Strong ignition spark and no fuel Correct operation of all systems Only a weak battery

Ignition system service information in the ILM helps the parts technician to:

Ignore manufacturer specifications Select correct coils, modules, sensors and spark plugs for the application Supply any component that is in stock Decide which engine to install

A spark plug that is oil fouled may indicate:

High alternator output Engine mechanical problems such as worn rings or valve guides Correct ignition system operation Low engine coolant level only

Ignition wires should be routed and clipped correctly to:

Increase radio noise Prevent cross firing and avoid contact with hot or moving parts Reduce alternator speed Increase starter torque

An open circuit in a crankshaft position sensor will MOST likely result in:

No effect on engine operation No start because the control module cannot determine engine position High charging voltage Starter running continuously

When inspecting an ignition system component catalogue, a parts technician should note:

Coil and plug specifications, connector styles and system type for correct application Only the price of each component That any coil can be used on any engine That ILM information is not required