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Chapter 28 Ignition System Diagnosis and Service Service Precautions • Always turn the ignition switch off before disconnecting any system wiring • Do not touch any exposed connections while the engine is running or cranking Misfires • Something that prevents complete combustion • Can cause lack of power, poor fuel mileage, excessive emissions, and rough running • Ignition misfires can be caused by weak spark, fouled plug, faulty coil, primary or secondary faults, or incorrect plug gap Causes of Detonation • • • • Excessively advanced ignition timing Engine overheating Excessively lean mixtures Gasoline with too low octane rating Preignition Types of Ignition System Problems • Common – Problems affect all cylinders – Components include parts of the primary circuit and secondary circuit up to the distributor rotor • Uncommon – Problems affect one or more but not all cylinders – Components include plug wires and plugs Visual Inspection • No-start conditions mostly caused by primary circuit faults • Common symptoms of ignition problems include: – Hard starting – Rough idle – Engine stalling Primary Circuit • • • • • Inspect wiring and connections Perform wiggle test Examine ignition switch Check charging system and battery Inspect for moisture affecting wiring Sensors • Inspect magnetic pulse generators and Halleffect sensors and wiring • The non-magnetic reluctor can become magnetized and affect pulse generator signal Control Modules • Use transistors as switches • Modules can be mounted in distributor, remotely, or as part of PCM • Check for clean and tight mounting • May require heat-conductive silicone grease on mounting surface DIS Systems • A problem on one cylinder may affect its companion cylinder • Separate primary circuit for each coil • Test each coil’s primary and secondary wiring • Proper plug torque can affect ground circuit Coil-On-Plug Systems • Individual coil problems affect only one cylinder • Coils can be tested with ohmmeter • Cylinder misfire codes can result from injector, plug, coil, or engine mechanical problems Spark Plugs • Carefully twist plug boot and pull wire from spark plug • Use compressed air to blow any debris from the base of the plugs • Remove the plug and inspect threads and cylinder head for damage • Never remove plugs from a hot engine Inspecting Spark Plugs • Note deposits and degree of electrode wear • Normal color is grey or tan • Gap should increase no more than 001” for every 10,000 miles of service • Reading spark plugs can reveal a variety of engine conditions Worn Spark Plug Regapping Spark Plugs • The gap of both new and used plugs should be checked • Do not reduce gap by tapping plug, use needle-nose pliers or gapping tool • Keep ground electrode in line with positive Spark Plug Installation • • • • • • Wipe dirt from plug seats Verify plugs are correct replacements Adjust the gap as needed Check whether anti-seize should be used Install and hand tighten Torque to specifications Secondary Ignition Wires • Inspect for cracks and worn insulation • Check boots for cracks and hard, brittle conditions • Check resistance with an ohmmeter • Replace as a set • Properly route to avoid cross-firing ... cap, and wires Distributor Cap and Rotor Service • Arcing between cap and rotor terminals deteriorates terminals • Replace both cap and rotor together • Make sure both are fully seated • Arrange... silicone grease on mounting surface Secondary Circuit • Inspect plug wires and boots for damage • Ensure correct wire routing • Check coil(s) for cracks • Inspect cap and rotor No Spark Diagnosis. .. rating Preignition Types of Ignition System Problems • Common – Problems affect all cylinders – Components include parts of the primary circuit and secondary circuit up to the distributor rotor •