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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 1998 🢒 Chevy P12 Chassis 🢒 Engine 🢒 Engine Controls - 7.4L 🢒 Electronic Ignition (EI) System Diagnosis

Refer to

Cell 20: Ignition Coils


Object Number: 260837 Size: FS
Cell 10: Hot in Run and Start Fuses
Cell 11: Eng RH, LH, PCM 1, and Fuel Pump Fuses
Cell 11: Eng RH, LH, PCM 1, and Fuel Pump Fuses
Engine Controls Components
Electronic Ignition (EI) System Description
Cell 20: Fuel Pump Control
Cell 20: Knock Sensors, VSS, Camshaft and Crankshaft Position Sensors
OBD II Symbol Description Notice
ESD Notice

Circuit Description

A Crankshaft Position (CKP) sensor determines the engine crankshaft position. The sensor is mounted and protrudes into the engine front cover. The sensor is near a slotted reluctor ring on the crankshaft. The rotation of the slotted reluctor ring causes a magnetic flux change in the sensor. This produces a voltage signal from the electronic Ignition Control Module (ICM). The signal creates the reference pulses needed by the Powertrain Control Module (PCM). These signals trigger the correct ignition coil to fire, at the correct time.

The ignition system on this engine uses an individual ignition coil/module for each cylinder. The PCM controls the ignition system operation. There are eight Ignition Control (IC) circuits, one per cylinder, that connect the PCM and the ignition coil/modules. Each ignition coil/module has an ignition positive voltage circuit, a ground circuit, and a reference low circuit. The PCM causes a spark to occur by grounding the IC circuit, which signals the ignition module to trigger the ignition coil and fire the spark plug. The PCM controls the sequencing and timing.

Diagnostic Aids

The following may cause an intermittent:

    • Check for poor connections. Check for adequate terminal tension. Refer to Body and Accessories/Wiring for proper procedure.
    • Corrosion
    • Mis-routed harness
    • Rubbed through wire insulation
    • Broken wire inside the insulation

. For an intermittent condition, refer to Symptoms .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

Important: Be sure to use the same diagnostic equipment for all measurements.

  1. This step will identify the misfiring cylinder(s). The spark tester requires a minimum of 25,000 volts to operate. It may be necessary to use the spark tester on all of the cylinders because the ignition system may provide enough voltage to run the engine but not enough to operate a spark plug under a heavy load. If you were sent here from the Engine Cranks But Will Not Run table, check for a faulty connection at the engine ground terminal.

    2.

  2. This step determines if the malfunction is affecting one cylinder or an entire bank of the ignition system.

    3.

  3. This test checks for a short to voltage at the ignition control (IC) signal circuit between the ignition coil/module and the PCM.

    4.

  4. This test will determine which side of the 8-way connector the malfunction is located.

    5.

  5. This test checks for a short to ground at the ignition control (IC) signal circuit between the PCM connector and the 8-way connector.

    6.

  6. This step completes the testing of the ignition system for a problem that will cause an entire bank to malfunction.

Electronic Ignition System Check

Step

Action

Value(s)

Yes

No

1

Did you perform the the Powertrain On-Board Diagnostic (OBD) System?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Install a scan tool
  2. Perform the Cylinder Power Balance Test.
  3. Disconnect the ignition wire(s) from the spark plug(s) that corresponds to the cylinder(s) that did not indicate the specified value of RPM drop.
  4. Install spark tester J 26792 to a ground.
  5. Start the engine.

Does the spark jump the tester?

50-200 RPM

Go to Step 5

Go to Step 3

3

Visually/physically inspect the ignition wire(s) for the following conditions:

    • Chaffing of the insulation.
    • Cracks in the insulation
    • Burned or cracked boot(s)
    • Improper seating of terminals at the spark plug(s)
    • Improper seating of terminals at the ignition coil/module(s)

Was a problem found and repaired?

Go to Step 43

Go to Step 4

4
  1. Remove the ignition wire(s) for the cylinder(s ) that did not indicate spark.
  2. Measure the resistance of the ignition wire using the DMMJ 39200

Is the ignition wire resistance less than the specified value?

700ohms

Go to Step 10

Go to Step 25

5

Remove the spark plug(s) from the cylinders that corresponds to the cylinder(s) that did not indicate the specified value of RPM drop.

Does the spark plug appear to be OK?

50-200 RPM

Go to Step 6

Go to Step 7

6
  1. Swap the suspected spark plug with another cylinder.
  2. Operate the vehicle under the same conditions that the symptom occurred.

Important:: If the Injector Coil Test Procedure checks to be OK, refer to Engine /Engine Mechanical .

Did the symptom move with the spark plug?

Go to Step 27

Go to

Fuel System Diagnosis

7

Are the spark plugs oil or coolant fouled?

lRefer to Engine /Engine Mechanical

Go to Step 8

8

Important:: If the Fuel system checks to be OK, refer to Engine /Engine Mechanical.

Are the spark plugs fuel fouled?

Go to Fuel System Diagnosis

Go to Step 9

9

Important:: If the Injector Coil Test Procedure checks OK, refer to Engine /Engine Mechanical

Inspect the spark plugs for any signs of the following conditions;

    • Cracks
    • Wear
    • Improper gap

Were any of the above conditions found?

Go to Step 26

Go to Fuel Injector Solenoid Coil Test

10

Was no spark present at only one cylinder?

Go to step 11

Go to step 18

11
  1. Turn OFF the ignition
  2. Disconnect the ignition coil/module electrical connector at the cylinder that did not have spark.
  3. Turn ON the ignition.
  4. Connect a J 35616-200 test lamp to battery ground, probe the ignition positive voltage terminal.

Does the test lamp illuminate?

Go to step 12

Go to Step 28

12
  1. Connect a J 35616-200 test lamp to the ignition positive voltage circuit at the coil/module electrical connector.
  2. Probe the ground circuit at the coil/module electrical connector.

Does the test lamp illuminate?

Go to step 13

Go to Step 29

13
  1. Turn ON the ignition.
  2. Connect a J 35616-200 test lamp to the ignition positive voltage circuit at the coil/module electrical electrical connector.
  3. Probe the reference low circuit at the coil/module electrical connector.

Does the test lamp illuminate?

Go to step 14

Go to step 31

14
  1. Connect a J 39200 DMM, set on the AC Hertz setting, to the ignition control signal circuit and battery ground.
  2. Start and idle the engine.

Is the frequency within the specified values?

3.0-2.0- Hz

Go to step 34

Go to step 15

15
  1. Turn ON the ignition leaving the engine OFF.
  2. Connect a J 39200 DMM, set on the DC setting, to the ignition control signal circuit, at the electrical connector, and battery ground.
  3. Is the voltage greater than the specified value?

1.0 volt

Go to step 35

Go to step 16

16
  1. Turn OFF the ignition.
  2. Disconnect the ignition coil/module electrical harness 8-way connector.
  3. Connect a J 39200 DMM, set on the AC Hertz setting, to the igniton control signal circuit (PCM side) and battery ground.
  4. Start and idle the engine.

Is the frequency within the specified values?

3.0-2.0- Hz

Go to step 37

Go to step 17

17
  1. Turn the ignition OFF.
  2. Disconnect the PCM connector located on the opposite side of the manufacturers logo. Refer to Powertrain Control Module Replacement .
  3. Using a DMM J 39200 , check for continuity between the ignition control signal circuit and a battery ground.

Does the DMM indicate conitinuity?

--

Go to step 36

Go to step 23

18
  1. Turn OFF the ignition.
  2. Disconnect the Ignition coil/module electrical harness 8-way connector for the bank that had no spark.
  3. Turn the ignition ON leaving the engine OFF.
  4. Connect a J 35616-200 test lamp to battery ground.
  5. Probe the ignition positive voltage circuit at the ignition coil/module 8-way connector (PCM side).

Does the test lamp illuminate?

Go to step 19

Go to step 41

19
  1. Connect a J 35616-200 test lamp to battery positive voltage.
  2. Probe the ground circuit at the 8-way connector (PCM side).

Does the test lamp illuminate?

Go to step 20

Go to step 38

20
  1. Connect a J 35616-200 test lamp to battery positive voltage.
  2. Probe the reference low circuit at the 8-way connector (PCM side).

Does the test lamp illuminate?

Go to Step 21

Go to Step 33

21
  1. Turn OFF the ignition
  2. Reconnect the Ignition Coil/Module 8-way connector
  3. Disconnect an ignition coil/module electrical connector at a cylinder that did not have spark.
  4. Turn ON the ignition.
  5. Using a test lamp connected to battery ground, probe the ignition positive voltage terminal.

Does the test lamp illuminate?

Go to step 22

Go to step 40

22
  1. Turn OFF the ignition
  2. Reconnect the ignition coil/module 8-way connector
  3. Disconnect an ignition coil/module electrical connector at a cylinder that did not have spark.
  4. Connect a test lamp J 35616-200 to battery positive voltage.
  5. Probe the ground circuit at the connector

Does the test lamp illuminate?

Go to step 35

Go to step 30

23
  1. Turn the ignition OFF.
  2. Disconnect the PCM connector located on the opposite side of the manufacturers logo. Refer to PCM replacement.
  3. Connect a J 39200 DMM, set on the ohms setting, to the ignition control circuit at the PCM connector.
  4. Check the continuity of the ignition control circuit between the PCM connector and the 8-way connector using the DMM J 39200 .

Does the DMM indicate continuity?

--

Go to step 24

Go to step 39

24

Check for poor connections/terminal tension at the PCM harness connector. Refer to Body and Accessories/Wiring Systems for the proper procedure.

Was a problem found and repaired?

Go to step 43

Go to step 42

25

Replace the faulty ignition wire.

Is the action complete?

Go to Step 43

--

26

Replace or re-gap the spark plugs. If improper gap is found, adjust the spark plug gap using a wire type gauge.

Is the action complete?

Go to Step 43

--

27

Replace the faulty spark plug(s).

Is the action complete?

Go to step 43

--

28

Repair an open ignition positive voltage circuit between the ignition coil/module and the splice.

Is the action complete?

Go to step 43

--

29

Repair an open ground circuit between the ignition coil/module and the splice.

Is the action complete?

Go to step 43

--

30

Repair an open ground circuit between the 8-way connector and the splice.

Is the action complete?

Go to step 43

--

31

Repair an open reference low circuit between the ignition coil/module and the splice.

Is the action complete?

Go to step 43

--

32

Repair an open reference low circuit between the 8-way connector and the splice.

Is the action complete?

Go to step 43

--

33

Repair an open reference low circuit between the 8-way connector and the PCM.

Is the action complete?

Go to step 43

--

34

Replace the ignition coil/module.

Is the action complete?

Go to step 43

--

35

Repair a short to voltage to the ignition control signal circuit between the ignition coil/module and the PCM.

Is the action complete?

Go to step 43

--

36

Repair a short to ground at the ignition control signal circuit between the 8-way connector and the PCM.

Is the action complete?

Go to step 43

--

37

Repair a short to ground or an open at the ignition control signal circuit between the 8-way connector and the ignition coil/module.

Is the action complete?

Go to step 43

--

38

Repair an open ground circuit between the 8-way connector and the engine ground.

Is the action complete?

Go to step 43

--

39

Repair an open ignition control signal circuit between the 8-way connector and the PCM.

Is the action complete?

Go to step 43

--

40

Repair an open ignition positive voltage circuit between the 8-way connector (engine side) and the splice .

Is the action complete?

Go to step 43

--

41
  1. Inspect the fuse for an open.
  2. If the fuse is open, check ignition positive voltage circuit for a short to ground and replace the fuse.
  3. If the fuse is not open, repair open at ignition positive voltage circuit between the 8-way connector and the fuse.

Is the action complete?

Go to step 43

--

42
  1. Replace the PCM.
  2. Program the new PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

Go to step 43

--

43

Operate the vehicle within the conditions under which the original symptom was noted.

Does the system now operate properly?

System OK

Go to step 2