Ignition

Ignition Systems 4/21/2005

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Engine Performance

Ignition SystemsIgnition Systems

Donald JonesBrookhaven College

Engine Performance

Spark and IgnitionSpark and Ignition

• An ignition spark must have two qualities:• Heat to ignite the

air fuel mixture• Duration sufficient

to start the combustion process properly

Engine Performance

Heat and IgnitionHeat and Ignition

• Increasing the number of electrons flowing across the spark plug electrodes increases the heat

• The spark’s heat must be sufficient to ignite the fuel molecules and maintain flame propagation

Engine Performance

Spark DurationSpark Duration

• Spark duration is the length of time a spark is maintained

• Typically between .8 and 1.5 milliseconds• Lean mixtures are difficult to ignite

because the fuel molecules are far apart• Rich mixtures are easier to ignite

because the fuel molecule are closer together

Engine Performance

Ignition OperationIgnition OperationA. Spark plug wireB. Distributor capC. RotorD. Coil wireE. Distributor bodyF. ReluctorG. Pickup coilH. Ignition control

moduleI. Ignition coilJ. Spark plugs

Engine Performance

Primary CircuitPrimary Circuit1. Ignition switch2. Ignition coil3. ICM transistor4. ICM5. PCM6. Other primary circuit

components include the camshaft sensor or crankshaft position sensor and related wiring


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Engine Performance

Secondary CircuitSecondary Circuit

• Coil• Coil wire• Distributor cap• Rotor• Spark plug wire• Spark plugs

Engine Performance

Ignition CoilIgnition Coil• Converts low voltage

into high voltage• Primary windings

• 12 to 14.5 volt circuit

• Secondary windings• Up to 50 kilovolts on

distributor ignition systems • Up to 100 kilovolts on

distributorless ignition systems

Engine Performance

• The ICM controls the flow of current through the coil’s primary windings

• Current flow through the primary windings creates a magnetic field

• The ICM opens the primary circuit and the magnetic field collapses

• A high voltage is induced in the coil’s secondary windings

Ignition Control ModuleIgnition Control Module

1. Primary windings2. ICM3. ICM transistor4. Magnetic field

Engine Performance

Coil Dwell TimeCoil Dwell Time

1. Coil primary circuit2. ICM3. ICM transistor4. Magnetic field5. Primary saturation6. Primary current off

Engine Performance

Secondary WiresSecondary Wires• To reduce radio

interference the core is made with carbon particle impregnated strands

• Easily damaged if handled improperly

• 4000 to 6000 ohms of resistance per foot

Engine Performance

Spark PlugsSpark Plugs

• Connector• Ceramic insulator• Resistor• Center electrode• Air gap• Side electrode


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Engine Performance

Base Engine TimingBase Engine Timing• Ignition timing refers when

the spark plugs fire in relation to the piston’s position during the compression stroke

• For the engine to operate efficiently the combustion process should be completed approximately 23 degrees after top dead center

Engine Performance

Spark TimingSpark Timing• Each combustion

process takes about the same time to complete

• Spark must occur sooner as engine speed increases

• Timing is advanced to occur earlier during the compression stroke

• Spark advance typically retards as engine speed decreases

• Ignition timing is also affected by variables such as load, air/fuel ratios, engine temperature, intake air temperature and intake air density

Engine Performance

Ignition RequirementsIgnition Requirements

• Starting• Idle• Cruise• Acceleration

Engine Performance

Secondary WaveformSecondary WaveformA. Firing voltage

• Primary current flow interrupted

• Voltage required to jump across spark plug electrode gap

B. Spark duration• Time in milliseconds

secondary current is flowing

C. Dwell time• Time primary current is

flowing and saturating coil’s magnetic field

Voltage is displayed vertically

Time is displayed horizontally

Engine Performance

StartingStarting• Requirements for

ignition during cranking are typically lower than for other operating modes

• Richer air/fuel mixtures are used during cranking, which reduces secondary voltage requirements

Engine Performance

IdleIdle• Ignition timing can vary

greatly to help control idle rpm

• Spark is advanced if rpm is too low and retarded if rpm is too high

• KV requirements at idle can also vary from 8KV to 16KV due to engine and ignition system design differences


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Engine Performance

CruiseCruise• Cruise is a light load

engine operating condition• Secondary voltage

requirements are less than those required for acceleration mode

• Spark duration increases because the spark KV requirements are low

• As KV requirements increase, spark duration will decrease

1. Secondary voltage

2. Spark duration

Engine Performance

AccelerationAcceleration• Combustion

pressures in the cylinder are very high

• Ignition secondary voltage increases to overcome high resistance caused by these high pressures

Engine Performance

Profile Ignition PickupProfile Ignition Pickup• A CMP Hall Effect Unit

provides a digital signal, called PIP, to the ICM and PCM

• This signal provides the PCM with engine RPM and crankshaft position

1. PIP2. PCM3. Coil4. ICM transistor5. ICM6. Distributor

Engine Performance

Spark OutputSpark Output• SPOUT is a digital signal

produced by the PCM that directs the ICM to open the coil’s primary ground circuit

• The ICM may use only the rising edge of SPOUT to control timing or may also use the falling edge of SPOUT to control dwell time

1. PCM2. Spout3. Coil4. ICM transistor5. ICM

Engine Performance

Distributor Ignition SystemDistributor Ignition System1. PIP - profile ignition pickup2. PCM3. Tachometer signal4. IDM - ignition diagnostic

monitor 5. Coil6. ICM transistor7. ICM8. SPOUT - spark output9. Distributor - CMP

Engine Performance

Distributorless IgnitionDistributorless Ignition• One coil pack is used for each

cylinder pair• Two spark plugs are paired to each

coil pack• The two plugs are wired in series

and fired simultaneously• One cylinder is on the compression

stroke and its mate cylinder is on the exhaust stroke

• Because of the exhaust stroke waste spark, each spark plug is fired every 360 degrees of crankshaft rotation


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Engine Performance

DIS Coil Pack OperationDIS Coil Pack Operation

1. Ignition switch2. Spark plugs3. Coil pack4. PCM

Engine Performance

Typical DIS ComponentsTypical DIS Components• ICM

• May be integrated into PCM

• CMP• PCM• Plug wires• Coil packs• Spark plugs• CKP

Engine Performance

VRS and Trigger WheelVRS and Trigger Wheel• The CKP sensor has 35

teeth spaced ten degrees apart which produce an AC signal

• The missing tooth provides a Cylinder ID signal for the PCM

• Can the PCM differentiate whether a cylinder is on the compression or exhaust stroke?

Engine Performance

Typical DIS SignalsTypical DIS SignalsCrankshaft Position

• 60˚ BTDC• 10˚ BTDC• TDC• 20˚ ATDC

Signals5. IDM6. COIL 1 current7. CMP - Hall Unit8. SPOUT9. CKP - VRS

Engine Performance

Coil On Plug IgnitionCoil On Plug Ignition

1. Camshaft2. CMP3. PCM4. RFI capacitor5. COP coil6. Spark plug7. Trigger wheel8. CKP

Engine Performance

Ignition Related SymptomsIgnition Related Symptoms

• There are four ignition related conditions that can cause driveability symptoms• No spark• Loss of spark• Weak spark• Improper ignition

timing


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Engine Performance

Spark Related ConditionsSpark Related Conditions

XXXPoor Fuel Economy

XSpark Knock

XXLoss of Power

XXMisses/Runs Rough

XXStalls

XXXNo Start

TimingWeak SparkLoss of SparkNo SparkConcern

Engine Performance

Basic TestingBasic Testing

• Common tools• Test light• DVOM• Spark tester• Break out box• Oscilloscopes• Timing light• Scan tools

Engine Performance

Common Circuit TestsCommon Circuit Tests• Primary Circuit

• General circuit condition• Coil voltage supply• Coil primary circuit

ground• Coil primary resistance• Coil dwell - saturation

• Secondary Circuit• General circuit condition• Coil secondary

resistance• Secondary wire

resistance• Secondary required

voltage• Spark duration• Spark plug condition

Ignition

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