Electronic Ignition (EI) System Diagnosis General
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
Circuit Description
When any condition is suspected to be caused by, or related to the Ignition System, the first step in diagnosis should be to check for stored powertrain control module (PCM) DTCs. Diagnose all DTCs before further action is taken.
The Ignition System Check provides a means of testing ignition system performance and references other tables for specific ignition system conditions.
Test Description
The number below refers to the step number on the Diagnostic Table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | ||||
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | |
2 | Are any powertrain control module (PCM) DTCs set? | -- | Diagnosis those DTCs first | Go to Step 3 |
3 | Start the engine. Is there a no start or hard start condition? | -- | Go to Step 4 | Go to Step 5 |
4 |
Is voltage reading greater than the specified value? | 10 V | Go to Step 8 | |
5 | Drive vehicle and note any driveability symptoms. Is a miss, stumble, or hesitation noted? | -- | Go to Step 6 | |
6 | Are any other driveability symptoms noted? | -- | Go to Symptoms | Verify Repair |
Does engine speed decrease? | -- | System OK | ||
8 | Check the IC module fuse and repair open or short to ground in CKT 239. Is the action complete? | -- | -- | |
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.
-
Ensure good DVM contact when measuring spark plug resistance. When manufactured the normal resistance for the spark plug is 3000-8000 ohms.
-
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.
-
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 DVM contact when measuring spark plug resistance. When manufactured the normal resistance for the spark plug is 3000-8000 ohms. A suspected ignition system miss may actually be a fuel system problem. Perform the Fuel System Check, if it has not yet been performed.
-
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 Step 2 | |
2 | Key On and connect the scan tool. Are any PCM DTCs set? | -- | Go to those DTCs first
| Go to Step 3 |
3 | Perform Injector Balance Check using the scan tool and note cylinders with no engine speed or idle quality change. Refer to Fuel Injector Balance Test . Were any cylinders noted? | -- | Go to Step 4 | Go to Step 17 |
4 | Were two companion cylinders, 1&4, 2&5, 6&7, or 3&8, noted? | -- | Go to Step 10 | Go to Step 5 |
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 | Go to Step 22 | Go to Step 6 |
6 | Remove affected spark plug. Does spark look OK? | -- | Go to Step 7 | Go to Step 23 |
Measure resistance or affected spark plug. Does spark plug measure less than the specified value? | 15,000 ohms | Go to Step 8 | Go to Step 23 | |
Does spark jump tester gap? | -- | Secondary ignition system OK. Go to Fuel System Diagnosis | Go to Step 9 | |
9 |
Does spark jump tester gap? | -- | Go to Step 25 | Go to Step 26 |
Does spark jump tester gap? | -- | Go to Step 12 | Go to Step 11 | |
Switch affected coil with another coil and repeat the Injector Balance Check using the scan tool. Did the fault follow the affected coil? | -- | Go to Step 25 | Go to Step 26 | |
12 | Reinstall all spark plugs and wires. Start engine and inspect for visible/audible arcing. Is ignition system arcing externally? | -- | Go to Step 27 | Go to Step 13 |
13 |
Does spark jump tester gap? | -- | Go to Step 14 | Go to Step 25 |
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 | Go to Step 22 | Go to Step 15 |
15 | Remove affected spark plugs and check for wear, damage, or fouling. Do both plugs look OK? | -- | Go to Step 16 | Go to Step 24 |
Measure resistance of affected spark plugs. Do both spark plugs individually measure less than the specified value? | 15,000 ohms | Secondary ignition system OK. Go to Fuel System Diagnosis
| Go to Step 24 | |
17 |
Does spark jump tester gap on all eight cylinders? | -- | Secondary ignition system OK. Go to Fuel System Diagnosis
| Go to Step 18 |
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? | -- | Go to Step 25 | Go to Step 19 | |
19 |
Is either spark plug wire shorted to ground or more than the specified value? | 15,000 ohms | Go to Step 22 | Go to Step 20 |
20 | Remove affected spark plugs and check for wear, damage, or fouling. Do both plugs look OK? | -- | Go to Step 21 | Go to Step 24 |
21 | Measure resistance of affected spark plugs. Do both spark plugs individually measure less than the specified value? | 15,000 ohms | Go to Step 26 | Go to Step 24 |
22 | Replace the spark plug wire. Is the action complete? | -- | -- | |
23 | Replace the spark plug. Is the action complete? | -- | -- | |
24 | Replace the affected spark plug. Is the action complete? | -- | -- | |
25 | Replace the affected coil. Is the action complete? | -- | -- | |
26 | Replace the IC Module. Is the action complete? | -- | -- | |
27 | Repair the source of arcing. Is the action complete? | -- | -- |
