Circuit Description
The enhanced ignition system uses the crankshaft position (CKP) sensor in order to provide a timing input to the control module. Ignition control (IC) spark timing for each cylinder is based on this input. The control module provides the ignition timing signal to the ignition control module (ICM) to control the ignition coil. Each timing pulse detected by the ICM allows it to energize the ignition coil. A large secondary ignition voltage is induced in the secondary coil by the primary coil. This high voltage is switched to the correct spark plug by the distributor.
Diagnostic Aids
Check the following:
The IC control circuit for an intermittent short to ground.
Check for the following when the distributor rotor does not rotate while the engine is cranking:
| • | A broken distributor drive shaft. |
| • | A worn distributor drive gear or camshaft timing chain and gears. |
An intermittent may be caused by any of the following conditions:
| • | A poor connection |
| • | Rubbed through wire insulation |
| • | A broken wire inside the insulation |
Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
The battery should be fully charged prior to any tests.
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Perform the OBD system check before proceeding unless it was already performed.
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Checks for proper output from the enhanced ignition system. The spark tester requires a minimum of 25,000 volts to operate. This check can be used in case of an ignition miss, because the system may provide enough voltage to run the engine but not enough to operate a spark plug under heavy load.
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This test separates the distributor cap, rotor and ignition wires from the ignition coil in order to help identify a secondary ignition system problem.
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This test checks the ignition control module, connections, and wiring.
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This test begins to determine if the VCM is providing a signal to the ignition control module. If the VCM is not providing a signal to the ignition control module, the problem exists between the ignition control module and the VCM.
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This test checks for a basic engine mechanical problem.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||||||
Is adequate spark present? | -- | Go to Symptoms | ||||||||||
Is adequate spark present? | -- | |||||||||||
4 | Measure the coil wire resistance using a DMM. The resistance should be approximately the specified value. Is the resistance within the specified value? | 1000 ohms/inch | ||||||||||
Is the test lamp flashing while cranking the engine? | -- | |||||||||||
6 |
Is the test lamp ON? | -- | ||||||||||
7 |
Does the voltage measure above the specified value? | 10.0 V | ||||||||||
8 |
Is the circuit open? | -- | ||||||||||
9 |
Does the voltage measure above the specified value? | 10.0 V | ||||||||||
10 | Probe the ignition control module harness connector terminal C with a test lamp connected to B+. Is the test lamp ON? | -- | ||||||||||
Is the voltage between the specified values? | 1.0-4.0 V | |||||||||||
12 |
Are any of these conditions present? | -- | ||||||||||
Did the distributor rotor turn? | -- | Go to Symptoms | ||||||||||
14 |
Is the circuit open? | -- | ||||||||||
15 | Probe the ignition control (IC) circuit at the VCM C3 connector with a test lamp connected to B+. Is the test lamp ON? | -- | ||||||||||
16 |
Is the test lamp ON? | -- | ||||||||||
17 |
Is the action complete? | -- | -- | |||||||||
18 |
Is the action complete? | -- | -- | |||||||||
19 | Check for a poor ignition control module connection. Did you find a problem? | -- | ||||||||||
20 | Check for a poor coil connection . Did you find a problem? | -- | ||||||||||
21 | Check for a poor VCM connection. Did you find a problem? | -- | ||||||||||
22 | Repair the open ignition control module ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
23 | Repair the open IC circuit between the VCM and the ignition control module. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
24 | Repair the grounded IC circuit between the VCM and the ignition control module. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
25 | Repair the short to voltage in the IC circuit between the VCM and the ignition control module. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
26 | Repair the open in the tachometer signal circuit between the ignition coil and the ignition control module. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
27 | Repair the short to ground in the tachometer signal circuit between the ignition coil and the ignition control module. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
28 | Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||
29 | Replace the ignition coil. Refer to Ignition Coil and Ignition Coil Module Replacement in Engine Electrical. Is the action complete? | -- | -- | |||||||||
30 | Replace the coil wire. Refer to Ignition Coil and Ignition Coil Module Replacement in Engine Electrical. Is the action complete? | -- | -- | |||||||||
31 | Replace the distributor rotor. Refer to Camshaft Position Sensor Replacement for distributor rotor replacement. Is the action complete? | -- | -- | |||||||||
32 | Replace the distributor cap. Refer to Camshaft Position Sensor Replacement for distributor cap replacement. Is the action complete? | -- | -- | |||||||||
33 | Replace the ignition control module. Refer to Ignition Coil and Ignition Coil Module Replacement in Engine Electrical. Is the action complete? | -- | -- | |||||||||
34 |
Important: The replacement VCM must be programmed. Replace the VCM. Refer to VCM Replacement/Programming . Is the action complete? | -- | -- | |||||||||
35 | Operate the vehicle within the conditions under which the original symptom was noted. Does the system now operate properly? | -- | System OK |
