GM Grand Am/Achieva/Calais/Skylark/Somerset 1985-98

Diagnosis and Testing

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Service Precautions

The HEI coil secondary voltage output capabilities can exceed 40,000 volts. Avoid body contact with the HEI high voltage secondary components when the engine is running, or personal injury may result.

To avoid damage to the ECM or other ignition system components, do not use electrical test equipment such as battery or AC powered voltmeter, ohmmeter, etc. or any type of tester other than specified.



When making compression checks, disconnect the ignition switch feed wire at the distributor.
 
Never allow the tachometer terminal to touch ground, as damage to the module and/or ignition coil can result.
 
To prevent Electrostatic Discharge damage, when working with the ECM, do not touch the connector pins or soldered components on the circuit board.
 
When handling a PROM, CAL-PAK or MEM-CAL, do not touch the component leads. Also, do not remove the integrated circuit from the carrier.
 
Never allow welding cables to lie on, near or across any vehicle electrical wiring.
 
Leave new components and modules in the shipping package until ready to install them.
 
When performing electrical tests on the system, use a high impedance multimeter, digital voltmeter (DVM) J-34029-A or equivalent.
 
Never pierce a high tension lead or boot for any testing purpose; otherwise, future problems are guaranteed.
 

Ignition System CheckSee Figures 1, 2, 3 and 4

The accompanying wire schematics and charts can be used to diagnose and troubleshoot some HEI system component problems.



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Fig. Fig. 1: Ignition system diagnostic check-1985-86 2.5L engine



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Fig. Fig. 2: Schematic of ignition system wiring-1985-86 2.5L engine



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Fig. Fig. 3: Ignition system diagnostic check-2.0L engine



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Fig. Fig. 4: Schematic of ignition system wiring-2.0L engine

Engine Cranks But Will Not Run

  1. Check that the fuel quantity is OK.
  2.  
  3. Turn the ignition switch ON . Verify that the SERVICE ENGINE SOON light is ON.
  4.  
  5. Install the scan tool and check the following:
  6.  



Throttle Position Sensor (TPS): if over 2.5 volts, at closed throttle, check TPS for intermittent, open or short to ground, or faulty TPS.
 
Coolant: if less than 86°F (30°C), check Coolant Temperature Sensor (CTS) for intermittent, open or short to ground, or faulty CTS.
 

  1. Connect spark checker, J 26792 or equivalent, and check for spark while cranking. Check at least 2 wires.
  2.  

  1. If spark occurs, reconnect the spark plug wires and check for fuel spray at the injector(s) while cranking. If no spark is visible, inspect the system for a trouble code. Refer to Driveability & Emissions Controls .
  2.  
  3. If no spark occurs, check for battery voltage to the ignition system. If OK, use the ignition diagnosis chart.
  4.  

Electronic Spark Timing (EST) Circuit

  1. Clear any codes which are present.
  2.  
  3. Idle the engine for approximately 1 minute or until Code 42 sets. If Code 42 does not set, Code 42 is intermittent.
  4.  
  5. If Code 42 sets, turn the ignition OFF , then disengage the ECM connectors.
  6.  

  1. Turn the ignition switch ON .
  2.  
  3. Using an ohmmeter to ground, probe the ECM harness connector, at the EST circuit. Place the ohmmeter selector switch in the 1000-2000 ohms range. The meter should read less than 1000 ohms.
  4.  

  1. If not, check for a faulty connection, open circuit or faulty ignition module.
  2.  
  3. If OK, probe the bypass circuit with a test light to battery voltage.
  4.  
  5. If the test light is ON, disconnect the ignition 4-way connector and observe the test light.
  6.  

  1. If the test light goes OFF, the problem is a faulty ignition module.
  2.  
  3. If the test light stays ON, the bypass circuit is shorted to ground.
  4.  

  1. If the test light remains OFF, from Step 5, again probe the bypass circuit with the test light connected to battery voltage, and the ohmmeter still connected to the EST circuit and ground. As the test light contacts the bypass circuit, resistance should switch from under 1000 to over 2000 ohms.
  2.  

  1. If it does, reconnect the ECM and idle the engine for approximately 1 minute or until Code 42 sets. If Code 42 sets, it is a faulty ECM.
  2.  
  3. If not, Code 42 is intermittent.
  4.  

  1. If the results are not as indicated in Step 7, disconnect the distributor 4-way connector. With the ohmmeter still connected to the bypass circuit, resistance should have gone high (open circuit).
  2.  
  3. If not, the EST circuit is shorted to ground.
  4.  
  5. If OK, the bypass circuit is open, faulty connections or faulty ignition module.
  6.  

When the problem has been corrected, clear codes and confirm Closed Loop operation and no SERVICE ENGINE SOON light.

 
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