Ignition System Service

1
Ignition System Service

• Chapter 38

2
Objectives

• Diagnose common ignition system problems
• Service ignition systems and distributors
  correctly
• Install a distributor and adjust ignition timing
• Operate an oscilloscope and interpret scope
  patterns

3
Ignition System Service and Repairs

• Tune-up
• Originated when cars had ignition points
• Today referred to as a 30,000- or 60,000-mile
  service
• 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

4
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

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Spark Plug Diagnosis

• Temperature of spark plug
• Relates directly to combustion chamber
  temperature
• 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
  charged
• Fouled plugs
• Oil and ash deposits

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Spark Plug Diagnosis (contd.)

• 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

9
Repairing Damaged Spark Plug Threads

• Spark plug threads are sometimes stripped
• Can be avoided if a ratchet is never used
• Stripped threads can be replaced with a thread
  insert
• Tapered seat spark plugs
• Cannot be repaired with thread inserts

10
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 Service

• 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

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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 pump

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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 crank
• 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

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Electronic Ignition System Service

• 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 (contd.)

• 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 (contd.)

• 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 (contd.)

• 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
  others

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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
• DSO
• Tool used to diagnose electronic problems