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Ignition System Service

Ignition System Service. Chapter 38. 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. Ignition System Service and Repairs. Tune-up

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Ignition System Service

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  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

  5. 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

  6. Spark Plug Diagnosis (cont’d.) • Checking and adjusting the spark plug gap • Gap is set at the factory • Always double-check before installation

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. Other Distributor Repair Service • Distributors have gears and bushings • Wear out or break • Distributor drive gear • Can become stripped • Shaft bushings • Can wear out

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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

  20. 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

  21. 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 others

  22. 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

  23. 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

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