Electronic Ignition (EI) System Diagnosis General Diagnosis
When any condition is suspected to be caused by or related to the ignition control system, the first step in diagnosis should be to check for stored PCM DTCs. Diagnose all DTCs before further action is taken. If no DTCs are stored and the condition is still present, refer to the following:
| • | Ignition System Check |
| • | Symptoms |
Electronic Ignition (EI) System Diagnosis Ignition System Check
Refer to Electrical Schematic Diagrams for wiring view.
Circuit Description
The IC module determines crankshaft and camshaft position and fires the appropriate spark plug. The IC module also creates 4X and 24X reference pulses that are supplied to the PCM. The PCM uses these reference circuits to determine fuel delivery and spark timing. Most failures in the Ignition Control system will set a PCM DTC. Always perform the Powertrain OBD System Check and, if necessary, the Engine Cranks but Does Not Run diagnostic table BEFORE performing the Ignition System Check.
Test Description
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The Engine Cranks but Does Not Run table must be performed BEFORE using this diagnostic procedure.
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Observe the Engine Speed parameter on the scan tool while increasing spark RETARD by 10 degrees. The PCM will attempt to keep the engine speed at the Desired Idle during spark retard by slightly increasing spark advance. The engine speed may initially drop by 50 RPM then increase slightly to average 30 RPM less than the RPM observed during normal spark control.
If engine speed fails to decrease proceed to Step 4 of DTC P1350 diagnosis.
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Observe the scan tool status for the extended travel brake switch. Ensure that the extended travel brake switch status is not applied all the time. When the extended travel brake switch is applied the PCM will operates in Torque Management at high throttle angles causing timing and fuel reduction during acceleration.
Step | Action | Value(s) | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to the Powertrain OBD System Check | |||||||||
2 | Using a scan tool check for stored PCM DTC's. Are any DTC's set? | -- | Go to DTC's | |||||||||
Attempt to start and idle the engine. Refer to Test Descriptions . Does the engine start? | -- | |||||||||||
Does engine speed decrease as spark is retarded? | -- | Go to DTC P1350 diagnosis | ||||||||||
Is a Miss, Stumble, or Hesitation observed? | -- | Go to Secondary Ignition Check | ||||||||||
6 | Were any other driveability symptoms observed? | -- | Go to Symptoms | System OK | ||||||||
7 |
Does the testlight illuminate? | -- | Go to Step 11 | Go to Step 8 | ||||||||
8 | Connect the testlight between terminal C and a good engine ground. Does the testlight illuminate? | -- | ||||||||||
9 | Repair the open ground circuit to the IC module. Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
10 | Repair the cause of no voltage to the IC module. Possibilities include the following:
Is the repair complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- | ||||||||
11 |
Was terminal contact repaired? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | |||||||||
12 | Replace the IC module. Refer to IC Module Replacement . Is the replacement complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
Electronic Ignition (EI) System Diagnosis Secondary Ignition Check
Circuit Description
The Secondary Ignition Check tests for faulty spark plugs, plug wires, or IC Module/Coils. This table requires the J 26792 spark tester (ST-125).
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
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Ensure good DMM contact when measuring spark plug resistance. When manufactured the normal resistance for the spark plug is 900-2500 ohms but resistance growth up to 10K ohms is considered normal.
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J 26792 spark tester (ST 125) presents a more difficult load on the secondary ignition than a normal spark plug. If a miss, stumble, or hesitation is being caused by a spark plug not firing, the spark tester should also not fire.
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The companion spark plug shares the same ignition coil with the spark being tested (1-4, 2-5, 6-7, 3-8).
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If the no spark condition follows the suspected coil, that coil is faulty. Otherwise, the ignition module is the cause of no spark. This test could also be performed by substituting a known good coil for the one causing the no spark condition.
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Ensure good DMM contact when measuring spark plug resistance. When manufactured the normal resistance for the spark plug is 900-2500 ohms but resistance growth up to 10K ohms is considered normal. A suspected ignition system miss may actually be a fuel system problem. Perform the Fuel System Check, if it has not yet been performed.
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If the no spark condition follows the suspected coil, that coil is faulty. This test could also be performed by substituting a known good coil for the one causing the no spark condition.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Powertrain OBD System Check | |
2 | Key On and connect the scan tool. Are any PCM DTC(s) set? | -- | Go to those DTC(s) first
| |
3 | Perform Injector Balance Check using the scan tool and note cylinders with no engine speed or idle quality change. Were any cylinders noted? | -- | ||
4 | Were two companion cylinders, 1&4, 2&5, 6&7, or 3&8, noted? | -- | ||
5 | Check affected spark plug wire resistance to ground and resistance end to end. Is spark plug wire shorted to ground or more than the specified value? | 15,000 ohms | ||
6 | Remove affected spark plug. Does spark look OK? | -- | ||
Measure resistance or affected spark plug. Does spark plug measure less than the specified value? | 10,000 ohms | |||
Does spark jump tester gap? | -- | Secondary ignition system OK. Go to Fuel System Check
| ||
9 |
Does spark jump tester gap? | -- | ||
Does spark jump tester gap? | -- | |||
Switch affected coil with another coil and repeat the Injector Balance Check using the scan tool. Did the fault follow the affected coil? | -- | |||
12 |
Is ignition system arcing externally? | -- | ||
13 |
Does spark jump tester gap? | -- | ||
14 | Check affected spark plug wire resistance to ground and resistance end to end. Is spark plug wire shorted to ground or more than the specified value? | 15,000 ohms | ||
15 | Remove affected spark plugs and check for wear, damage, or fouling. Do both plugs look OK | -- | ||
Measure resistance of affected spark plugs. Do both spark plugs individually measure less than the specified value? | 10,000 ohms | Secondary ignition system OK. Go to Fuel System Check
| ||
17 |
Does spark jump tester gap on all eight cylinders? | -- | Secondary ignition system OK. Go to Fuel System Check
| |
Switch affected coil with another coil and repeat the spark plug tester test on all four cylinders of switched coils. Did the fault follow the affected coil? | -- | |||
19 |
Is either spark plug wire shorted to ground or more than the specified value? | 15,000 ohms | ||
20 | Remove affected spark plugs and check for wear, damage, or fouling. Do both plugs look OK? | -- | ||
21 | Measure resistance of affected spark plugs. Do both spark plugs individually measure less than the specified value? | 10,000 ohms | ||
22 | Replace the spark plug wire. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
23 | Replace the spark plug. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
24 | Replace the affected spark plug. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
25 | Replace the affected coil. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
26 | Replace the IC Module. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
27 | Repair the source of arcing. Is the action complete? | -- | Go to Powertrain Control Module Diagnosis for Verify Repair | -- |
