© 2012 Delmar, Cengage Learning Ignition System Service Chapter 38

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning Spark Plug Diagnosis (cont’d.) Checking and adjusting the spark plug gap –Gap is set at the factory Always double-check before installation

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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

© 2012 Delmar, Cengage Learning 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