Electronic Ignition System Diagnosis
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Electronic Ignition System Diagnosis
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Circuit/System Description
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This ignition system uses individual Ignition Coil assemblies for each cylinder. The engine control module (ECM) controls the spark events by transmitting the timing pulses on the ignition control circuits to the individual ignition coil assemblies in firing order sequence. Each ignition coil has the following circuits:
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An ignition voltage circuit
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An ignition control circuit
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This test procedure requires that the vehicle battery has passed a load test and is completely charged.
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There is an adequate supply of fuel in the fuel tank.
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When disconnecting electrical connectors or removing fuses and relays from a fuse block, always inspect both mating electrical terminals for corrosion and terminal tightness.
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Use the
EL 35616-E
Terminal Test Kit for any test that requires probing the underhood fuse block terminals, component wire harness terminals, or the ECM wire harness terminals.
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A slight to moderate resistance in the ignition voltage circuit can cause a misfire condition or a crank/no start concern.
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Extended engine cranking time, will foul the spark plugs with excessive fuel and cause a crank/no start condition.
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Schematic Reference
Engine Controls Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Electronic Ignition System Description
Electrical Information Reference
Scan Tool Reference
Control Module References
Special Tools
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EL 26792
HEI Spark Tester
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EL 35616-E
Terminal Test Kit
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For equivalent regional tools, refer to
Special Tools
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Circuit/System Verification
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Note
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Verify that the engine is in good mechanical condition before continuing with this diagnostic.
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Observe the engine controls schematic for the ignition module/coils, and review the ignition system specifications to verify the following concerns:
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The ignition modules/coils are correctly wired and connected
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The proper spark plug type
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The proper spark plug gap and torque
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1.
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Turn OFF the ignition.
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2.
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Note
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If the ignition fuse F9 is open, it will be necessary to test the spliced ignition circuits and the components for a short to ground.
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Inspect the fuse that supplies ignition voltage to the ignition module/coils.
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3.
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If fuse F9 is open, test all ignition voltage circuits to the T8 Ignition Coil for a short to ground.
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4.
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Disconnect the T8 Ignition Coil connector.
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5.
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Replace the open fuse F9 with a new fuse.
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6.
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Ignition ON, with the engine OFF
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7.
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Reconnect T8 Ignition Coil connector.
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8.
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If the fuse F9 opens when connecting the T8 Ignition Coil, then replace the T8 Ignition Coil.
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9.
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Ignition OFF, disconnect the T8 Ignition Coil electrical connector.
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10.
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Ignition ON, verify that a test lamp illuminates between the ignition voltage circuit terminal A and ground.
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11.
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If the test lamp does not illuminate test the T8 Ignition Coil Ignition Voltage Circuit for an open/high resistance.
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12.
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Verify that a test lamp illuminates between the T8 Ignition Coil Ground Circuit terminal B and B+.
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13.
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If the test lamp does not illuminate, test the T8 Ignition Coil Ground Circuit for an open/high resistance.
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14.
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Exchange the affected T8 Ignition Coil assembly with a known good assembly.
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15.
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Note
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An open/high resistance on the low reference circuit to the ignition control module may cause a misfire.
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Start and idle the engine. Observe the misfire counters on the scan tool.
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16.
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If the misfire or crank/no start is resolved, replace the T8 Ignition Coil/module assembly.
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17.
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If the misfire does not transfer with the suspect T8 Ignition Coil, measure the resistance of the ignition control circuit. The ignition control circuit should measure less than 5 Ω. If the circuit tests normal, replace the K20 Engine Control Module.
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Static Test
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Use the spark plug inspection procedure to verify the integrity of the spark plugs. Replace the spark plug if necessary.
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Note
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An erratic or weak spark is considered a no spark condition.
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Use the
EL 26792
HEI Spark Tester to verify the output of the T8 ignition coil. If no spark is detected across the gap of the spark plug tester, replace the T8 Ignition Coil assembly.
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Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
