GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1997 🢒 Safari - 2WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 Enhanced Ignition System Diagnosis

Enhanced Ignition System Diagnosis Overview

A misfire condition could cause a rough idle or engine misfire condition. A DTC which determines if the misfire is random or specific to 1 or 2 cylinders will accompany the misfire. A worn Distributor cap and rotor, a cracked Distributor cap, cross fire within the Distributor or across plug wires or worn spark plugs may result in a misfire. A faulty or mispositioned crankshaft sensor which will also be accompanied by a crankshaft sensor DTC may also cause a misfire. If a DTC sets, refer to that chart first before using the Enhanced Ignition system check.

Enhanced Ignition System Diagnosis System Check

Circuit Description

This system includes the Distributor, the ignition coil, the ignition control module, the secondary wires, spark plugs, the VCM and the crank sensor. The ignition system is controlled by the Vehicle Control Module (VCM). The VCM monitors the information from various engine sensors, computes the desired spark timing and controls the dwell and firing of the ignition coil via an (IC) line to the ignition control module.

Test Description

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

The battery should be fully charged prior to any tests.

  1. Perform the OBD system check before proceeding unless it was already performed. In order to disconnect the tachometer lead, it will be necessary to disconnect the gray ignition coil connector from the ignition coil and jumper the B terminal of the harness connector to the B terminal of the ignition coil using a fused jumper and terminal test adapter kit J 35616-A.

    2.

  2. Checks for proper output from the enhanced ignition system. The spark tester requires a minimum of 25,000 volts to fire. 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 fire a spark plug under heavy load. This test also separates the distributor cap, rotor and ignition wires from the ignition coil in order to help identify a secondary ignition system problem.

    3.

  3. This step determines if the proper available voltage exists in the primary ignition circuit. Also checks ignition coil and wiring.

    4.

  4. This check begins to determine if the VCM is providing a signal to the ignition coil module or not. If the VCM is not providing a signal to the ignition coil driver module, the problem exists between the distributor and VCM.

    5.

  5. This test checks the coil driver module, connections and wiring.

    6.

  6. This test checks the wiring from the VCM to the coil driver module and finally the VCM.

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Check the spark plug wires for open circuits, cracks or improper seating of terminals at the spark plugs, distributor and ignition coil before proceeding with the test.
  2. Check spark at plug with J 26792 spark tester or the equivalent while cranking. (If there is no spark on one wire, check a second wire). A few sparks then nothing is considered no spark.

Is adequate spark present?

--

Go to Hard Start

Go to Step 3

3
  1. Remove the coil wire from the ignition coil.
  2. Insert J 26792 spark tester into coil wire and clamp onto coil tower terminal.
  3. Crank the engine.

Is adequate spark present?

--

Go to Step 7

Go to Step 4

4
  1. Disconnect the ignition coil driver module connector.
  2. Turn the Ignition ON.
  3. With a DVM J 39200 , check voltage on terminals A and D to ground.

Do both terminals measure above the specified value?

10.0 Volts

Go to Step 5

Go to Step 13

5
  1. Connect a DVM J 39200 on the AC scale to the ignition coil driver module connector terminal B and ground.
  2. Crank the engine and observe the voltage.

Is the voltage between the specified values?

1.0-4.0 Volts

Go to Step 6

Go to Step 10

6

Probe the ignition coil driver module connector terminal C with test light to B+.

Is the test lamp illuminated?

--

Go to Step 12

Go to Step 20

7
  1. Check the coil wire resistance using a DVM J 39200 .
    2. • The resistance should be approximately the specified value.
    • If J 39200 indicates an open circuit or extremely high resistance, replace the coil wire.
  2. Retest for spark at spark plug using a J 26792 spark tester.

Is adequate spark present?

1000  ohms/inch

Go to Step 27

Go to Step 8

8
  1. Remove the distributor cap.
  2. Check for the following conditions:
    3. • Cracks
    • Carbon tracks
    • Or physical damage.

Did you find damage to the distributor cap?

--

Go to Step 19

Go to Step 9

9

With the distributor cap removed, crank the engine and check for rotation of the distributor rotor.

Does the distributor rotor turn?

--

Go to Step 18

Go to Step 17

10
  1. Turn the Ignition OFF.
  2. Disconnect the VCM Gray connector.
  3. Check for continuity between the VCM connector terminal Ignition Control (IC) circuit and the ignition coil driver module connector terminal B.

Is the circuit open?

--

Go to Step 22

Go to Step 11

11

With a test lamp to B+, probe the VCM harness terminal Ignition Control (IC) circuit.

Is the test light on?

--

Go to Step 23

Go to Step 26

12
  1. Reconnect the Ignition Control Module connector.
  2. Disconnect the Ignition Coil connector.
  3. Connect the test light to B+.
  4. Crank the engine.

Does the test lamp flash?

--

Go to Step 16

Go to Step 21

13

Do both of the terminals measure under the specified value?

10.0 Volts

Go to Step 14

Go to Step 17

14

Check the following:

    • A faulty ignition feed circuit to ignition coil
    • A grounded external ignition coil circuit.

Was a problem found?

--

Go to Step 19

Go to Step 24

15

Check the following:

    • The circuit from the ignition coil to terminal D of the Ignition Control Module for an open
    • A faulty ignition coil connection.

Was a problem found?

--

Go to Step 19

Go to Step 16

16
  1. Connect the test lamp to a ground.
  2. Disconnect the Ignition Coil connector.
  3. Turn the ignition ON.
  4. Probe terminal B of the Ignition Coil connector.

Is the test lamp on?

--

Go to Step 24

Go to Step 14

17
  1. Remove the distributor
  2. Inspect the distributor.

Was a problem found?

--

Go to Step 25

Refer to 6D4

18

Replace the spark plug wires.

Is the action complete?

--

Go to Step 27

--

19

Repair as necessary.

Is the action complete?

--

Go to Step 27

--

20

Repair open ignition coil driver module ground circuit. Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 27

--

21
  1. Check for a faulty ignition coil driver module connection.
  2. If OK, replace the ignition coil module. Refer to Engine Electrical On-Vehicle.

Is the action complete?

--

Go to Step 27

--

22

Repair the open IC circuit between the VCM and the ignition coil driver module. Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 27

--

23

Repair the grounded IC circuit between the VCM and the ignition coil driver module. Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 27

--

24

Replace the ignition coil. Refer to 6D4.

Is the action complete?

--

Go to Step 27

--

25

Replace the distributor. Refer to 6D4.

Is the action complete?

--

Go to Step 27

--

26
  1. Check for a faulty VCM connection.
  2. If OK, replace the VCM. Refer to VCM Replacement/Programming .

Is the action complete?

--

Go to Step 27

--

27

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

Does the system now operate properly?

--

System OK

Go to Step 1