Ignition System Service

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Transcript Ignition System Service

Ignition System Service
Chapter 38
© 2012 Delmar, Cengage Learning
• Diagnose common ignition system problems
• Service ignition systems and distributors
• Install a distributor and adjust ignition timing
• Operate an oscilloscope and interpret scope
© 2012 Delmar, Cengage Learning
Ignition System Service and
• Tune-up
– Originated when cars had ignition points
– Today: referred to as a 30,000- or 60,000-mile
• Can include replacement of all filters, belts, hoses,
and fluids
• A few engines require mechanical valve
measurement and adjustment
• Timing belt can also be part of a 60,000- or
90,000-mile service
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Spark Plug Service
• Important points
Use correct replacement plugs
Use the correct spark plug heat range
Check the size of the threads
Check to see if the old spark plug used a gasket
Check the reach or thread length
Tapered seat plugs can be difficult to remove
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
Spark Plug Diagnosis
• Temperature of spark plug
– Relates directly to combustion chamber
• Condition of used spark plugs
– Indicates condition of engine and fuel system
– Spark plug wear
• Some use double plat plugs
• Worn rounded electrode more surface area to be
– Fouled plugs
• Oil and ash deposits
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Spark Plug Diagnosis (cont’d.)
• Checking and adjusting the spark plug gap
– Gap is set at the factory
• Always double-check before installation
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Installing Spark Plugs
• Seal of the plug
– Can be ruined by overtightening
• Today's spark plugs
– Longer lifetime
• Indexing a spark plug
– High-performance procedure
• Usually used in high-compression racing engines
– Platinum plating on spark plug electrodes
reduces wear
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Repairing Damaged Spark Plug
• Spark plug threads are sometimes stripped
– Can be avoided if a ratchet is never used
– Stripped threads can be replaced with a thread
• Tapered seat spark plugs
– Cannot be repaired with thread inserts
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Spark Plug Cable Service
• Removing spark plug cables
– Must be a careful operation
• Determine internal structure of a cable is sound
– Check resistance with an ohmmeter
• Cable ends
– Terminal is crimped tightly to the cable
• Spark plug cables
– Installed in the holes around the distributor cap
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Distributor Ignition Service
• Distributor ignition systems
– Unique maintenance requirements
• Distributor cap and rotor service
– Distributor is cracked: carbon trail often forms
– Excessive resistance in secondary system:
creates a hole at the tip of the rotor
– Distributor cap has an aligning feature
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Ignition Timing
• Ignition timing on electronic ignition (EI) systems
– Controlled by the powertrain control module
– A timing light is a strobe light
– Timing is changed by loosening the distributor
body and rotating in one direction or the other
– Older cars with points: point gap adjusted with a
feeler gauge
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Electronic Ignition Distributor
• Normal electronic ignition service on DI systems
– Limited to replacement of the rotor
• No spark
– Trigger may not be opening primary circuit
– Bad module
– Bad ignition coil
• Best test for a bad module
– Test the other parts of the system first
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
Other Distributor Repair Service
• Distributors have gears and bushings
– Wear out or break
• Distributor drive gear
– Can become stripped
• Shaft bushings
– Can wear out
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Distributor Installation
• Align the timing mark on the damper with the
pointer on the timing cover
– If distributor is installed 180 degrees off,
backfiring will occur and engine will not run
• On pushrod engines the distributor will not drop
all the way into the block
– Bottom is not aligning with the drive lug on the oil
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Static Timing
• Ignition system can be static timed
– With the number one cylinder on its
compression, align the timing indicator at the
– Install distributor with rotor pointing to the
number one plug cable
– Rotate distributor body until the armature pole
piece aligns with permanent magnet
– Tighten the distributor holddown
© 2012 Delmar, Cengage Learning
© 2012 Delmar, Cengage Learning
Electronic Ignition System
• Determine problem cause
– Before replacing the part
• Important concepts
Ignition problem diagnosis: visual inspection
Ignition-related no start: use scan tool
Signal generator testing: different sensor types
Pickup coil testing and replacement: use
ohmmeter to test continuity
– Air gap measurement: use feeler gauge
– Hall switch testing: use scan tool
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Electronic Ignition System
Service (cont’d.)
– Scopes: oscilloscope is helpful for pinpointing
ignition and engine problems
– Ignition patterns: different scope pattern types
can be selected
– Spark line: horizontal line that begins at the
voltage level where electrons start to flow across
the spark plug gap
– Dwell section: represents the time that the
primary current is switched on
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Types of Scope Patterns
• Raster pattern
– Displays all cylinders
• Superimposed pattern
– Compares all cylinders
• Patterns are displayed one on top of the other
• Display pattern
– Displays all cylinders side by side
• Firing line heights can be compared
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Oscilloscope Tests
• Voltage test
– Popular with older contact point systems
• Reading a parade pattern
– Run the engine at 1,200-1,500 rpm for
oscilloscope tests
– Perform an acceleration load test by rapidly
snapping the throttle open and closed
• Reading a raster pattern
– Spark section
– Dwell section
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Oscilloscope Tests (cont’d.)
• Scope diagnosis of engine problems
– Engine problems can show up in a scope pattern
• Scope diagnosis of ignition problems
– When the engine is off, use a ground probe to
ground the spark plug end of a plug cable
• Stress test
– Parts are cooled or heated
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Oscilloscope Tests (cont’d.)
• Primary voltage ignition pattern
– Secondary pattern is the best pattern for
displaying an ignition system
• Shows primary as well as secondary current flow
• Primary current ramp test
– Allows you to watch the current
• As it ramps up and at its peak
• Vacuum waveforms
– Problem cylinders will have less vacuum than
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Other Scope Tests
• Tests of individual components
– Can be done with a scope
• Hall switch, contact points, and LED
– Give a square wave
• Pickup coil
– Gives an AC sine wave
– Increases with speed
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Other Diagnostic Instruments
• Other test instruments have become common
– Computer systems
• Store trouble codes
– Handheld tools
• Read codes and interpret data
• Tool used to diagnose electronic problems
© 2012 Delmar, Cengage Learning