Theory Module - JustAnswer

Engine controlmodule (ECM)

Powertransistor

Ignitioncoil Spark plug 4

Powertransistor

Ignitioncoil

Spark plug 3

Spark plug 2

Spark plug 1

Crankshaft position sensorCamshaft position sensorKnock sensor (some engine types)Barometric pressure sensorIntake air temperature sensorEngine coolant temperature sensorThrottle position sensorClosed throttle position switch

INPUTS

16.01Theory Module

��

��

After completing this module, you will be able toapply your knowledge of ignition systemoperation, to diagnose ignition relatedperformance problems more efficiently.

This technical training module is for use by professional Mitsubishi Motors dealershipservice technicians. The descriptions and procedures in this publication supplementexisting service manuals, technical service bulletins and other documents provided byMitsubishi Motor Sales of America, Inc. (MMSA). As a result, the use of these sourcesmay be required to ensure a proper repair.

SAFETY IS YOUR RESPONSIBILITY

A Caution alerts you to the possibility of damage to either tools,equipment, or to the vehicle itself. A Caution recommends a proceduremust be done in a certain way to avoid potential problems resulting fromimproper technique or method.

A Warning alerts you to the highest level of risk. Warnings inform you aprocedure must be done in a particular way to minimize the chances of anaccident that could result in personal injury or even loss of life.

WARNING

CAUTION

NOTE

Within this module you will find Notes, Cautions and Warnings. These references provideguidance to help you do your job efficiently and safely. The definition for these terms arelisted below.

The purpose of a Note is to help you do your job more efficiently. A Notemay also provide additional information to help clarify a particular point orprocedure.

No part of this publication may be reproduced, storedelectronically, or transmitted in any form or by any means withoutprior written approval from Mitsubishi Motor Sales of America, Inc.MMSA reserves the right to make changes in the descriptions,specifications or procedures without prior notice or obligation.

When you see a Note, Caution or Warning, be sure you understand the message beforeyou attempt to perform any part of a service procedure. Also keep in mind it is impossiblefor MMSA to anticipate or evaluate every service situation a technician may encounter.For that reason, you have the final responsibility for personal safety - yours and thoseworking around you. Be sure to always wear proper protective clothing and safetyequipment, use the proper tools and follow the repair procedures as outlined in variousservice publications provided by MMSA.

Copyright � 1999 Mitsubishi Motor Sales of America, Inc.Corporate Technical Training Department

Distributor and Distributorless Ignition Systems

Theory Module 16.01 1 Mitsubishi Motor Sales of America

Apply knowledge of ignition system operation todiagnose ignition related performance problems moreefficiently.

• Explain the operation of distributor anddistributorless ignition systems.

• Identify and explain the function of each componentin both types of ignition systems.

• Identify possible component failures and how thosefailures affect ignition system performance.

• Explain the process of fault isolation within a circuitfor each ignition system component.

• Identify the types of ignition system failures that canset diagnostic trouble codes.

Review this material as needed. When you are ready,complete the Knowledge Check at the end of thismodule.

Your performance in completing this module may beevaluated for course credit.

Diagnosing Engine Management Systems #65 Videofor self–study (Optional)

About 1 hour, 15 minutes

MODULE GOAL

OBJECTIVES

DIRECTIONS

WHAT YOU WILL NEED

TIME TO COMPLETE

TO FINISH

FINISH



Module Signposts

ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ

Activity

Feedback

Refer to the appropriate service manuals,technical service bulletins or other relatedmaterial.

Refer to the related video material for moreinformation.

Perform the following activity and answerthe related questions.

Complete the Knowledge Check to verifyyour understanding of the material.

Video

Reference



The ignition system is used to produce a spark at theproper time to begin combustion of the air–fuelmixture in the combustion chamber. Mitsubishi Motorsvehicles use both distributor type and distributorlessignition systems.

16.01–1


Powertransistor

Ignitioncoil

Distributor

Spark plugs

1

3

4

2

Crankshaft position sensorKnock sensor (some engine types)Baro sensorIntake air temperature sensorEngine coolant temperature sensorThrottle position sensorClosed throttle position switch (some models)

�

�

�

�

�

�

�

INPUTS

The ECM uses several sensor inputs to determine theproper time to produce a spark. When the ECMdetermines that an ignition spark is needed, it controlsa power transistor to interrupt current flow through theignition coil primary winding.

As a result, high voltage is generated in the ignitioncoil secondary winding that is routed to a mechanicaldistributor. The distributor rotates according to a linkwith the engine mechanical system.

The distributor routes the high voltage to the correctspark plug (electrode gap). A spark jumps the gap toignite the air–fuel mixture. The ECM controls thepower transistor to energize the ignition coil primarywinding to prepare for the next spark.

OVERVIEW

Distributor Type Ignition System



16.01–2


Powertransistor

Ignitioncoil Spark plug 4

Powertransistor

Ignitioncoil

Spark plug 3

Spark plug 2

Spark plug 1

Crankshaft position sensorCamshaft position sensorKnock sensor (some engine types)Barometric pressure sensorIntake air temperature sensorEngine coolant temperature sensorThrottle position sensorClosed throttle position switch (some models)

�

�

�

�

�

�

��

�

INPUTS

A distributorless ignition uses the same sensor inputsas a distributor type ignition system. In addition, sincethe ECM has more than one power transistor andignition coil to control, the camshaft position sensorinput is critical to proper operation of a distributorlessignition system. The camshaft position sensor is onlyused to control fuel injection operation on engines witha distributor type ignition.

One ignition coil and power transistor is used for eachpair of spark plugs. Each spark plug fires twice percombustion cycle, once on the compression strokeand once on the exhaust stroke. Since the exhauststroke spark has no direct effect on combustion, it iscommonly referred to as a ”waste” spark.

A distributorless ignition system is typically morereliable, since there are no moving parts on the outputside of the system. Also, the work of generatingsufficient voltage to create a spark is divided upbetween multiple coils. Each coil has more time tobuild a magnetic field between ignition sparks.

Distributorless Ignition System



The function of the ignition system is to effectivelyproduce and control ignition spark to maximizecombustion efficiency during various engine operatingconditions. These operating conditions include:

• Engine speed

• Engine load

• Engine temperature

• Air temperature

• Altitude

• Throttle transitions

• Engine knock

The driver of the vehicle has limited input to theignition system. As the accelerator is depressed, athrottle position sensor circuit generates an inputsignal to the ECM. This input is used by the ECM (inaddition to others) to determine ignition timing.

FUNCTION



16.01–3

Ignition switch (IG1)

Ignitioncoil

Powertransistor


Distributor

Spark plugs

Camshaftpositionsensor

Crankshaftpositionsensor

5V

MFI Relay

Primarywinding

Secondarywinding

The Engine Control Module (ECM) uses signalsgenerated by the crankshaft position sensor todetermine the proper time to generate an ignitionspark.

The ECM uses inputs from other sensors that monitorambient conditions and the driver’s demand for powerto fine tune ignition timing for the most efficientcombustion.

To prepare for a spark, the ECM controls a powertransistor to start current flow through the ignition coilprimary winding. A magnetic field builds in thewinding.

When the ECM decides to generate a spark, thepower transistor is controlled to interrupt current flowthrough the primary winding. The magnetic fieldcollapses, generating a high voltage in the secondarywinding. The high voltage is routed through amechanical distributor to the correct spark plug.

SYSTEMSYSTEM OPERATION

Distributor Type Ignition



16.01–45V


Powertransistorassembly


Camshaftpositionsensor Ignition coil

assembly

ÒÒÒ ÒÒÒÒÒÒÒÒÒ ÒÒÒÒÒ

5V5V5V5V

Halleffectswitch

Halleffectswitch

Ignition switch (IG1)MFI Relay

A distributorless ignition system uses either two orthree ignition coils, depending on the number ofengine cylinders. Each ignition coil is controlled by adedicated power transistor (combined in oneassembly).

The input side of a distributorless system operates thesame as a distributor type system, except that thecamshaft position sensor input is critical for properoperation. The ECM uses this input to determinewhich ignition coil to control at a given moment.

A distributorless ignition coil secondary winding has aspark plug lead connected to each end. Therefore,spark plugs always operate in pairs. As a result, thistype of ignition coil generates 2 sparks per combustioncycle for each cylinder.

One spark (the power spark) is used to begincombustion and the other is a “waste” spark thatoccurs during the exhaust stroke. This spark doesn’tdirectly affect combustion, but results from keepingignition system design as simple as possible.

Distributorless Ignition



The inputs to the ECM are similar for distributor anddistributorless ignition systems. The two primaryinputs used by the ECM are the crankshaft positionsensor (CKP) and the camshaft position sensor (CMP)signals.

– Provides ECM with crankshaft positioninformation for control of ignition timing

(and fuel delivery)

� Function

� Types of sensors– Hall effect– Light emitting/photo diodes

16.01–5

The crankshaft position sensor senses the crankangle (piston position of each cylinder) and convertsthe position to a pulse signal. The ECM uses thisinformation (along with other inputs) to determine theproper time to generate a spark (and deliver fuel).

Mitsubishi uses two different types of crankshaftposition sensors: Hall effect switches or lightemitting/photo diodes.

Distributor–mounted

Crankshaft position sensor

Crankshaft–mounted

Crankshaftposition sensor

16.01–6

The Hall effect type CKP is used in two differentapplications. One style is mounted at the crankshaftand the other is mounted in a distributor, dependingon ignition system design.

COMPONENT OPERATION

Crankshaft Position Sensor (CKP)

Hall Effect CKP

ECM Inputs



Magneticfield

Magnetic field Hallswitch

Supplycurrent

Voltage

Voltage

–+

16.01–7

Supplycurrent

“Hall effect” is a term used to describe what happenswhen a magnetic field is applied 90 degrees to acurrent flowing through a conductor.

When this occurs, a usable voltage signal is createdas shown in the illustration. This voltage is called theHall voltage. The Hall voltage can be used to controla transistor.

A transistor is typically used to ground and unground areference voltage to generate a signal with afrequency that varies according to the quantity beingmeasured.

Theory of Operation



Magnetic flux shield plate forcrank angle sensor

Vane

CKP

Magnetic flux shield plate

Crankshaftsprocket

Crankshaft

16.01–8

Hallswitch

Magnet

CKP

Magnetic fluxshield plate

The Hall effect crankshaft position sensor convertsmechanical rotation of the crankshaft to an electricalsignal by using a magnetic field. The sensor containsa magnet and a Hall switch, separated by a magneticflux shield plate that rotates with the crankshaft. Theshield plate has windows at specific locations.

When a window passes between the magnet and Hallswitch, the magnetic field acts on the Hall switch,generating a Hall voltage. When the shield plate vaneseparates the magnet and Hall switch, the magneticfield is blocked and the Hall switch does not generatea voltage.

Mechanical Operation



0V5V


Ground

Sensorpower

MFI Relay

On

Hall effectswitch

V

5V

0VT

Crankshaft positionsensor signal

16.01–9

HallVoltage

Signallead


The Hall effect CKP has three wires: a 12 volt powersupply for operation of the Hall switch, a signal leadthat controls a 5 volt reference from the ECM, and aground.

When a magnetic field acts on the Hall switch, a Hallvoltage is generated. The Hall voltage is amplifiedand used to control a transistor in the CKP sensor.

When the transistor is turned on due to the presenceof the Hall voltage, the 5 volt reference voltage fromthe ECM is grounded, resulting in 0 volts detected bythe ECM.

Electrical Operation

Magnetic Field Present



.

5V

Ground

Sensorpower

5V

MFI Relay

Off

Hall effectswitch

T

V

5V

0V

16.01–10


No hallvoltage Signal

lead



Nearly 5V

When the magnetic field is blocked by the magneticflux shield plate, there is no Hall voltage. Thetransistor in the CKP sensor turns off and the 5 voltreference voltage from the ECM is ungrounded,resulting in nearly 5 volts detected by the ECM.

Since the magnetic flux shield plate rotates with thecrankshaft, the rate that the shield plate windows passthrough the CKP sensor changes with RPM.

As a result, the CKP sensor grounds and ungroundsthe 5 volt reference from the ECM at a frequency thatvaries with RPM. The pulsed signal frequency is ameasure of crankshaft rpm.

Late model vehicles with On–Board Diagnostics II(OBD–II), use a crankshaft mounted Hall type sensorto support misfire detection.

Magnetic Field Blocked

Signal Frequency ChangesWith RPM



Distributor

16.01–11

The light emitting/photo diode crankshaft positionsensor is used with most distributor–type ignitionsystems. The sensor is mounted in the distributor oris driven by the camshaft and includes a camshaftposition sensor in one assembly.

LightfromLED

Currentflow

+ –

16.01–12

A photo diode allows reverse current to flow through itwhen enough light is present, and operates as anormal diode with no light present.

Light Emitting/Photo DiodeCKP

Photo Diode Theory of Operation



Photodiodes

Crankshaftpositionsensorwindow

Lightemittingdiodes

16.01–13

Shieldplate

The light emitting/photo diode crankshaft positionsensor (CKP) converts the rotation of the camshaft ordistributor to an electrical signal using light. Thesensor consists of a light emitting diode (LED), aphoto diode, and a shield plate. The light emittingdiode and the photo diode are aligned facing eachother on opposite sides of the shield plate.

The shield plate rotates with the distributor orcamshaft. When a window passes between an LEDand a photo diode, the light from the LED activates thephoto diode, allowing current to flow through the photodiode. When the shield plate blocks the light from theLED, the photo diode does not allow current to flow.

Mechanical Operation



MFI Relay

Ground

Engine control module (ECM)

Lightfrom LEDreceivedthroughwindowin shieldplate

5V

CrankshaftPositionSensor

Distributor

5V

T

V

5V

0V

16.01–14


Signallead

LED

The light emitting/photo diode CKP has three wires: a12 volt supply for the LEDS, a signal lead that controlsa 5 volt reference from the ECM, and a ground.

As the shield plate rotates, the 5 volt reference signalfrom the ECM is grounded at specific intervals. Whenlight from an LED passes through a window in theshield plate, the photo diode is activated.

When the photo diode is activated, it carries the 5 voltreference voltage to a comparator in the sensor, andnearly 5 volts is detected at the ECM.

Electrical Operation

Light is Present



MFI Relay

Ground


Light fromLED isblockedby shieldplate

5V


Distributor

0V

T

V

5V

0V

16.01–15

Signallead


LED

When light from the LED is blocked by the shieldplate, the photo diode is not exposed to light. Thephoto diode turns off and becomes non–conductive.

As a result, the 5 volt reference voltage from the ECMis grounded and 0 volts is detected by the ECM.

Light is Blocked



Highfrequency,high rpm

Lowfrequency,low rpm

16.01–16

The signal created by both types of crankshaftposition sensors is the same. If viewed on anoscilloscope the signal is a 5 volt square wave thatrepresents the RPM of the crankshaft.

The frequency of the signal varies according to therotational speed of the crankshaft (which alsodetermines the speed of the camshaft and distributor).

Crankshaft Position SensorSignals



5V

5V

5V

Enginecontrolmodule(ECM)

Ground

T

V

5V

0V

Crankshaftposition

sensor signal

Open

16.01–17

Sensorpower

MFI Relay

Hall effectswitch

Open


Signallead

If any of the three circuits (power supply, referencevoltage, or ground) are open, the ECM will detect 5volts on the signal lead as long as the open is present.

A power supply failure would prevent the Hall effectswitch from turning on. An open ground wouldprevent the transistor in the sensor from grounding theECM reference voltage.

Diagnosing Crankshaft PositionSensors

Open Circuit



MFI relay

Ground


5V


Distributor

0V

T

V

5V

0V

16.01–18


Signallead

Short

If the 5 volt reference circuit is shorted to ground, theECM will detect 0 volts on the signal lead for as longas the short to ground occurs.

Short Circuit



Example of an inaccurate signaldue to a mechanical problem

16.01–19

Mechanical problems can also cause the ECM todetect improper voltages on the signal lead. If thesensor is positioned incorrectly or the shield plate isdamaged, incorrect signals can result.

� Misfire (intermittent failure)

� No start (total failure)

16.01–20

A total failure of a crank position sensor can result inan “engine cranks, but won’t start” condition. Amomentary failure (intermittent) can cause an enginemisfire.

The ECM does not have a failsafe program tooperate without the crankshaft sensor input.

CKP Mechanical Problems

Effects of a Faulty CrankshaftPosition Sensor



– Provides ECM with camshaft positioninformation for control of multiple ignition

coils

� Function

� Types of sensors

– Hall effect– Light emitting/photo diodes

16.01–21

The CMP senses the camshaft position and converts itto a pulse signal. The ECM uses this information tocontrol multiple ignition coils in a distributorlessignition system (and also sequential operation of thefuel injectors).

Mitsubishi uses two different types of camshaftposition sensors: Hall effect switches or lightemitting/photo diodes.

Electrically and mechanically, these sensors operatesimilar to the crankshaft position sensors explainedearlier. Refer to the crankshaft position sensor sectionfor a description of electrical and mechanicaloperation.

� Location

� Signal to the ECM

� Diagnostic strategy

16.01–22

Camshaft Position Sensor (CMP)

Differences in CMPCompared to CKP



Distributor–mounted

Camshaft position sensor

Crankshaft/Camshaftposition sensorassembly

Camshaft–mounted

Camshaft–mounted

Camshaft position sensor

16.01–23

Camshaft timingbelt sprocket

Mounting locations vary depending on the application.The camshaft position sensor can be mounted in thedistributor or at the camshaft.

On many distributor–type ignition systems, the CKPand CMP are mounted together in the distributor.

On distributorless ignition systems, the camshaftposition sensor is located at the camshaft.

Depending on the application, the CMP is located in aCKP/CMP assembly or at the camshaft timing beltsprocket.

Location



Referencepulse

Typical camshaft position sensor signal

5V

Photodiodes

Longreferencewindow

Lightemittingdiodes

Typical camshaft positionsensor shield plate

Camshaftposition sensorwindows(inner ring)

16.01–24

The signal generated by the camshaft position sensor(CMP) is a 5 volt square wave much like that of theCKP. However, due to the arrangement of thewindows in the shield plate, one pulse is longer thanthe others.

The ECM recognizes this pulse as top dead center(TDC) of the #1 piston on the compression stroke.

Late model engines have CMP sensors that generatedifferent numbers of pulses, depending on enginedesign. However, there will always be some type ofreference pulse to identify #1 piston TDC on thecompression stroke.

For example, CMP sensors used in late modeldistributor–type ignition systems generate only onepulse per rotation of the distributor. This CMP signalis used in combination with the CKP sensor signal todetermine exact crankshaft position.

CMP Output Signal



– Momentary failure after start–up will notresult in misfire

� Used by ECM only during start–up

� Diagnose electrically using sameprocedures as CKP sensor

16.01–25

Provides ignition coil control informationon distributorless ignition systems

The important thing to remember about diagnosing aCMP sensor problem is that the ECM does not requireinput from this sensor once the engine is running.

A momentary failure of the CMP sensor after theengine is running will not result in a misfire. A totallyfailed CMP sensor will result in different symptoms,depending on the type of ignition system.

On distributorless ignition systems, the ECM uses thisinput to determine which ignition coil to control at agiven moment. Loss of the CMP sensor input whileattempting to start the engine will result in incorrectignition coil control. The engine will misfire to varyingdegrees, depending on specific ignition systemdesign. Stalling and hard starting are also likelysymptoms.

Models using a distributor–type ignition will start andrun well if the CKP sensor input is good, butsequential operation of the fuel injectors is affected.This will not necessarily reduce performance, but mayaffect fuel economy and exhaust emissions levels.

Electrically, diagnosing a CMP sensor is similar to aCKP sensor.

With some Chrysler systems, the engine will stoprunning if the CMP is disconnected.

Diagnosing CamshaftPosition Sensors




Ground

Knocksensor

16.01–26

When detonation occurs, the knock sensor generatesa small voltage proportional to the magnitude ofcylinder block vibration. This voltage is detected bythe ECM.

The ECM retards ignition timing varying amounts inresponse to knock sensor output. Maximum ignitiontiming retard is 21 degrees, and all cylinders areretarded equally.

On turbocharged vehicles, the knock sensor ignitiontiming retard program will only be active during apositive pressure (boost) condition.

If the knock sensor fails, ignition timing retardsapproximately 8 degrees.

Monitor ignition timing with the scan tool. With enginespeed around 2,000 rpm, tap lightly on the intakemanifold near the knock sensor with a metal tool. Ifthe knock sensor is functioning properly, ignition timingshould retard due to the tapping.

To verify knock sensor output, connect an oscilloscopeto the knock sensor signal lead and tap on the intakemanifold. The oscilloscope should show a knocksensor output voltage.

Check for opens and shorts at the knock sensor signallead using a DVOM.

Knock Sensor(if equipped)

Knock Sensor Diagnosis



The ECM uses additional inputs to fine tune ignitiontiming for maximum engine performance and fueleconomy, with minimum exhaust emissions. TheECM internal program responds to inputs as follows:

• Barometric pressure sensor – can add up to 7� ofignition timing at altitudes above 7,000 ft. Thebarometric pressure sensor has no effect if below1,500 ft.

• Engine coolant temperature sensor – can add 14�of ignition timing at or below –22�F. The enginecoolant temperature sensor has no effect on timingat temperatures above 95�F.

• Closed throttle position switch – provides input tothe ECM for target idle speed. Spark scatter(varying timing) is used below 1,000 rpm.

• Throttle position sensor – lowers timing advanceas voltage (throttle angle) increases (rate of increaseaffects ECM response). The throttle position sensorhas minimal effect on ignition timing when thethrottle angle is steady.

Additional ECM Inputs



Powertransistor


Base

5v

From ignitioncoil primary

Collector

16.01–27

Emitter

The power transistor operates like a conventionaltransistor, except it is designed to handle the relativelyhigh current (5 amperes is typical) that flows throughthe ignition coil primary winding to ground.

The power transistor grounds and un–grounds theignition coil primary winding based on low currentcontrol signals received from the ECM at the base ofthe transistor.

When 5 volts is applied to the base of the transistor,the collector–emitter junction of the transistorbecomes conductive and current flows through theignition coil primary winding to ground.

When the ECM switches off the 5 volt supply to thebase, the collector–emitter junction of the transistorbecomes non–conductive and current flow through theprimary winding is interrupted.

Distributor Type Ignition

ECM OUTPUTS

Power Transistor



16.01–28

Volts

Time

4

0

Waveramp upsection

When monitoring the voltage at the base of the powertransistor, it is normal to see the voltage “ramp up” asshown in the illustration. This is because the voltageat the base of the power transistor increases ascurrent flow through the ignition coil primary windingincreases.

If the power transistor control signal waveform looksdifferent, it may indicate an ignition coil primarywinding that is internally shorted or has abnormallyhigh resistance.

In either case, the resulting voltage generated in theignition coil secondary winding would be weak.

Power Transistor Control SignalCharacteristics



16.01–29

Terminals

Primarywinding

Secondarywinding

Core

An ignition coil is actually a transformer that converts12 volts at a relatively high current (approximately 5amperes) to a high voltage at low current(approximately 10,000 volts at 6 milliamperes) thatcan jump a gap and create a spark.

The actual voltage and current that results dependson the resistance of the gap that the spark must jump.

Ignition Coil



16.01–30

Switch open (powertransistor off), novoltage, no current

+

–12V

Primarywinding

No voltageor current

Secondarywinding

Switch closed (powertransistor on), voltageis applied and currentflow begins

Primarywinding

Secondarywinding

Primarywinding

Magnetic field stabilized

Secondarywinding

Primarywinding

Secondarywinding

+

–12V

+

–12V

+

–12V

Magnetic field expands

Switch closed (powertransistor on), voltageis applied and currentflow remains constant

Switch open (powertransistor off), novoltage, no current

Magnetic field collapses

Voltageinduced

High Voltageinduced

No voltageor current

As current begins to flow through the primary winding,a magnetic field builds slowly, due to the initialresistance of the primary winding and the effect ofinductance. Since the magnetic field builds slow, theresulting secondary winding voltage is too low to jumpthe spark plug gap. When the magnetic fieldstabilizes, no voltage is generated in the secondarywinding.

When current stops flowing through the primarywinding, the magnetic field collapses very quickly. Asthe rapidly moving magnetic field collapses throughthe secondary winding, a high voltage is generated.This voltage is routed to the correct spark plug gapwhere the resulting current flow across the gapgenerates a spark.

Ignition Coil Magnetic Field



The ignition coil primary winding can develop an open,a partial open (high resistance), an internal short or ashort to ground. The same problems can occur withthe secondary winding. Any of these problems willresult in reduced output from the coil and possibledamage to a power transistor if current flow throughthe primary becomes excessive.

16.01–31

Sparkplugs

Cap

Rotor

Distributor

To powertransistor

Ignitioncoil

Ig 1

The distributor is a mechanical device that distributesspark to the proper cylinder. High voltage travels fromthe center terminal of the distributor cap (connected tothe ignition coil secondary winding) through a contactat the center of the rotor and to the correct distributionterminal in the cap (connected to a spark plug througha high voltage lead). The distributor is driven directlyby the camshaft.

Problems with a distributor can result fromcomponents that cause secondary voltage meant for aspark plug to leak to ground or to the high voltagecircuit of an incorrect cylinder. The distributor cap androtor and plug wires are normally maintenance items.If replaced according to a normal maintenanceschedule, the chance of voltage leakage is minimized.

Other problems that can occur with a distributor resultfrom mechanical drive problems, such as worn rotorshaft bearings or incorrect installation resulting in therotor being in the wrong position.

Distributor

Diagnosing Distributor Problems

Diagnosing Ignition Coil Problems



16.01–32

The spark plug provides a precision gap for highvoltage generated from the ignition coil to jump,resulting in a spark in the cylinder. The spark plug isdesigned to ensure that voltage applied to the centerelectrode does not leak to ground before beingapplied to the gap. In addition, spark plugs aredesigned to maintain a certain temperature range atthe gap for controlled combustion.

Assuming that the correct spark plug is installed,problems typically result from a gap that is too large,too small or excessively worn. In addition, a sparkplug can become fouled with carbon, fuel or oil,resulting in high voltage that leaks to ground, ratherthan jumping the gap. This results in a weak spark orno spark at all.

Spark Plug

Diagnosing Spark Plug Problems



5V


Power transistors(in one assembly)

Ignition coils(in one assembly)

ÒÒ ÒÒ ÒÒÒÒ ÒÒÒÒÒÒ

Ignition switch Ig1

5V5V 16.01–33

Typical power transistorassembly

Power transistor operation for distributorless ignitionsystems is the same as that for distributor types. Theonly real difference is in the packaging. Depending onthe number of engine cylinders, two or three powertransistors may be packaged in one assembly. TheECM controls each separately.

Distributorless Type Ignition

Power Transistor



5V


Powertransistors

Ignition coilassembly

ÒÒ ÒÒÒÒÒÒ ÒÒÒÒ

Ignition switch Ig1

5V 5V 0V

5V5V 16.01–34

Primary coils onleft, secondarycoils on right

Off

On0V

Path ofcurrentflow

Ignition coils for Mitsubishi distributorless ignitionsystems have two spark plugs connected to thesecondary winding of each coil.

A 4 cylinder engine uses 2 coils packaged into oneassembly and a 6 cylinder engine uses 3 coilspackaged into one assembly. Each coil is controlledby a separate power transistor.

Since both ends of the secondary winding areconnected to spark plugs, both plugs fire together.

Current flow travels in a loop from one end of thesecondary winding to a spark plug, to the cylinderhead and back through the other spark plug to theopposite end of the secondary winding.

A distributorless ignition system requires each plug tofire twice as often as in a distributor type system, onceduring compression and once during the exhauststroke. The exhaust stroke spark is known as a wastespark, since it does not support combustion.

Ignition Coil



� Typical problems detectable with anignition analyzer

16.01–35

– Insufficient voltage from the ignition coil secondary winding– Intermittent misfire– Spark plug conditions– Open or shorted ignition coil primary or secondary winding– Malfunctioning/damaged distributor cap or rotor (if equipped)

Many ignition system problems occur on the outputside of the system: power transistors, ignition coils,spark plug wires or spark plugs, or the distributor (ifequipped).

An ignition analyzer can help diagnose an ignitionproblem. An ignition analyzer waveform is a graphicalrepresentation of the changing voltage in thesecondary side of the ignition coil, plug wires, andspark plug gap(s) over time.

Understanding a normal ignition analyzer waveformcan help to identify abnormal patterns when they arepresent. The ignition analyzer connects to the hightension spark plug leads through an inductive pickupand displays a waveform that shows ignition systemperformance.

The ignition analyzer can detect several different typesof problems in the ignition system. Each portion of thewaveform indicates how certain components arefunctioning.

Diagnosing Ignition SystemOutput Problems

Using An Ignition Analyzer



16.01–36

Firingline

Zeroline

Dwell

Sparkline Intermediate

section

Kilo

volt

s

Time

15

0

The firing line begins at the moment the powertransistor interrupts current flow through the ignitioncoil primary winding. This induces a high voltage intothe secondary winding.

The height of the firing line represents the initialvoltage required to jump the spark plug gap. At idle,this value is normally 5 to 15 KV with no more than a3 KV variation between cylinders.

The spark line is the voltage across the plug gap whilethe spark is actually jumping the gap. This voltage isless than the firing line voltage, because the gap isionized (charged), lowering the resistance of the gap.

It is normal to see slight voltage oscillations in thespark line as resistance across the gap changesslightly due to slight variations in the air–fuel mixture.

The small spike at the end of the spark line representsthe point that the spark stops, interrupting current flowthrough the secondary winding.

When current flow stops flowing across the gap, thesecondary winding becomes unloaded, resulting in aslight voltage spike in the secondary winding.

The duration of the spark line is based on theavailable coil voltage and the total secondary circuitresistance.

Generic Ignition Waveform

Firing Line

Spark Line



The intermediate section of the waveform representsthe remaining secondary voltage as it dissipates andeventually goes to zero volts.

It is normal to see 3 or more oscillations here, ascurrent attempts to flow back and forth in the opensecondary circuit (at the remaining voltage available,the plug gap creates an open secondary circuit).

The dwell section indicates how long the primarywinding is energized as a result of power transistoroperation. The oscillations in voltage are a result ofthe magnetic field build–up in the ignition coil. Thelength of the dwell section will vary with changes inengine speed and load.

– Large spark plug gap– High wear of spark plug electrode– Abnormally high compression– Lean air–fuel mixture– High resistance in secondary circuit

� High firing line

– Small spark plug gap– Fouled spark plug– Abnormally low compression– Rich air–fuel mixture– Leak in secondary circuit

� Low firing line

16.01–37

A high firing line can result from problems that make itdifficult to create a spark in one or more cylinders. Asa result, the coil must generate more voltage to jumpthe gap.

A low firing line can result from problems that make iteasier to create a spark, or current has found analternate path to ground.

Waveform Problems

Intermediate Section

Dwell Section

Firing Line



Spark line is high and short.

Spark plug gap is too large

Spark line is low, long and sloping.Also, the second half of the spark lineis missing (possible misfire).

Spark plug gap is too small

Spark line is high and short. Very difficultto distinguish from excessive plug gap.

Spark plug cable disconnected,creating multiple sparks

Spark line is low, long and sloping.However, there is almost no spark linedistortion.

Spark plug gap is fouled

16.01–38

The height and length of the spark line can tell a lotabout ignition system performance. The illustrationabove shows some examples of spark line problems.

A spark line that begins at a higher voltage thannormal (2–5 KV) and has a steep downward slope canindicate high resistance outside the cylinder in thesecondary circuit.

A spark line that begins normally but slants upwardcan indicate high resistance inside the cylinder. Sparkis established normally, but resistance affects the flowof current across the gap. If the firing line is normal,the problem may be combustion related.

Spark Line



16.01–39

1

Cylinder numbers and firing order

2 3 4 5 6

The ignition analyzer can show the performance ofindividual cylinders. It can also be used to comparespark quality from one cylinder to another.

This helps identify a problem with one cylinder, sparkplug or lead. If the ignition system is distributorless,specific problems related to an individual coil or powertransistor can be detected.

The analyzer can help determine whether a misfire israndom or isolated to specific cylinders. This can beuseful in eliminating certain ignition components whenperforming a diagnosis.

Comparison of IndividualCylinders



Use the following questions to see how well youunderstand the material in this module. If you don’tknow an answer, look it up. If you answer a questionincorrectly, read the material covering that topic againuntil you are sure you understand the concept.

Mark the following statements as True or False:

1. A distributor type ignition system requires acamshaft position sensor input on start–up forignition to occur on all cylinders.

True False

2. A distributorless ignition system utilizes one powertransistor and one ignition coil to produce ignitionspark for all cylinders.

True False

3. A distributor type ignition system utilizes an ignitioncoil pack to distribute spark.

True False

Fill in the blanks in the following sentences:

4. When current flow in the ignition coil primary winding is interrupted and the magnetic field collapses, a is inducedinto the ignition coil secondary winding.

a. square wave

b. high current

c. low voltage

d. high voltage

5. The power transistor in a distributor type ignition system is switched on and off by the

.

a. distributor rotor

b. ignition switch

c. camshaft position sensor

d. engine control module

Feedback

KNOWLEDGE CHECK



6. The crankshaft position sensor converts crankshaftrotation to a that isused by the engine control module.

a. variable AC signal

b. magnetic signal

c. piezo signal

d. DC square wave signal

From the following, select the most correctanswer:

7. In a distributorless ignition system, which of thefollowing components is used to complete theground circuit of the ignition coil primarywinding?

a. power transistor

b. secondary winding

c. rotor

d. spark plug

8. How many primary windings are present in a fourcylinder engine with a distributorless ignition control system?

a. 1

b. 2

c. 3

d. 4

9. How many power transistors are utilized in a sixcylinder engine with a distributor type ignition control system?

a. 1

b. 2

c. 3

d. 4



10. In a distributorless ignition system using twoignition coils to provide spark for four cylinders:

a. all four sparks are positive polarity

b. all four sparks are negative polarity

c. two sparks are positive polarity, two sparks are negative polarity.

d. all four sparks alternate between positive and negative polarity.

Mitsubishi Motor Sales of America, Inc. 2/00

Copyright 2014 - 2015 Service Repair Solutions, Inc.

Date post:	01-Oct-2021
Category:	Documents
Upload:	others
View:	2 times
Download:	0 times

Theory Module - JustAnswer

Documents