GM Malibu/Cutlass 1997-2000

Diagnosis and Testing

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SERVICE PRECAUTIONS




CAUTION
The ignition coils secondary voltage output capabilities are very high-more than 40,000 volts. Avoid body contact with ignition high voltage secondary components when the engine is running, or personal injury may result.

Before beginning any diagnosis and testing procedures, visually inspect the components of the ignition system and engine control systems. Check for the following:



Discharged battery
 
Damaged or loose connections
 
Damaged electrical insulation
 
Poor coil and spark plug connections
 
Ignition module connections
 
Blown fuses
 
Damaged vacuum hoses
 
Damaged spark plugs
 

Check the spark plug wires and boots for signs of poor insulation that could cause cross-firing. Make sure the battery is fully charged and that all accessories are off during diagnosis and testing. Make sure the idle speed is within specification.


NOTE
To avoid damage to the Powertrain Control Module (PCM) 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 performing electrical tests on the system, use a high impedance multimeter or digital voltmeter. Use of a 12 volt test light is not recommended.
 
To prevent electrostatic discharge damage, when working with the ECM or PCM, 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 pierce a high tension lead or boot for any testing purpose; otherwise, future problems are almost guaranteed.
 
Leave new components and modules in the shipping package until ready to install them.
 
Never disconnect any electrical connection with the ignition switch ON unless instructed to do so in a test.
 

SYSTEM DIAGNOSIS



The PCM uses information from the MAP and coolant sensors, in addition to rpm to calculate spark advance as follows:



Low MAP output voltage-more spark advance.
 
Cold engine-more spark advance.
 
High MAP output voltage-less spark advance.
 
Hot engine-less spark advance.
 

Therefore, detonation could be caused by low MAP output or high resistance in the Engine Coolant Temperature (ECT) sensor circuit, and poor performance could be caused by high MAP output or low resistance in the coolant sensor circuit.

On OBD II systems, if the engine cranks and does not run or immediately stalls, the following diagnostic test must be used to determine if the malfunction is in the EI system or fuel related.

SECONDARY SPARK TEST



The best way to perform this procedure is to use a spark tester (available at most automotive parts stores). Three types of spark testers are commonly available. The Neon Bulb type is connected to the spark plug wire and flashes with each ignition pulse. The Air Gap type must be adjusted to the individual spark plug gap specified for the engine. The last type of spark plug tester looks like a spark plug with a grounding clip on the side, but there is no side electrode for the spark to jump to. The last two types of testers allows the user to not only detect the presence of spark, but also the intensity (orange/yellow is weak, blue is strong).



Click image to see an enlarged view

Fig. This spark tester has an adjustable air-gap for measuring spark strength and testing different voltage ignition systems

2.4L Engine

NOTE
You will need 3 standard-style spark plug wires of the approximately the same length to perform this test on the 2.4L engine.

  1. Remove the four Ignition Control Module (ICM) cover bolts; refer to the procedure in this section.
  2.  
  3. Remove the ICM and ignition coil as an assembly
  4.  
  5. Remove the 4 spark plug boots and retainers from the coil housing cover.
  6.  
  7. Install the 3 standard spark plug wires onto the housing spark contacts, leaving one for testing.
  8.  
  9. Install the other ends of the spark plug wires onto the 3 corresponding spark plugs.
  10.  
  11. Reinstall one boot and retainer onto the remaining housing spark contact.
  12.  
  13. Connect the spark plug boot to the spark tester and ground the tester to an appropriate location on the engine.
  14.  
  15. Crank the engine and check for the presence of spark, and also the intensity at the tester.
  16.  
  17. If spark exists at the tester, the ignition system is functioning properly.
  18.  
  19. If necessary, repeat the procedure for remaining spark plug contacts.
  20.  
  21. If spark does not exist at the spark plug tester, perform diagnosis of the ignition system using individual component diagnosis procedures.
  22.  

3.1L Engine
  1. Disconnect a spark plug wire at the spark plug end.
  2.  
  3. Connect the plug wire to the spark tester and ground the tester to an appropriate location on the engine.
  4.  
  5. Crank the engine and check for the presence of spark, and also the intensity at the tester.
  6.  
  7. If spark exists at the tester, the ignition system is functioning properly.
  8.  
  9. If necessary, repeat the procedure for remaining spark plug wires.
  10.  
  11. If spark does not exist at the spark plug tester, perform diagnosis of the ignition system using individual component diagnosis procedures.
  12.  

CYLINDER DROP TEST




CAUTION
The ignition coils secondary voltage output capabilities are very high-more than 40,000 volts. Avoid body contact with ignition high voltage secondary components when the engine is running, or personal injury may result.

The cylinder drop test is performed when an engine misfire is evident. This test helps determine which cylinder is not contributing the proper power. The easiest way to perform this test is to remove the plug wires one at a time from the cylinders with the engine running.

2.4L Engine


Click image to see an enlarged view

Fig. These pliers are insulated and help protect the user from shock as well as the plug wires from being damaged


NOTE
You will need 4 standard-style spark plug wires of the approximately the same length to perform this test on the 2.4L engine.

  1. Remove the four Ignition Control Module (ICM) cover bolts; refer to the procedure in this section.
  2.  
  3. Remove the ICM and ignition coil as an assembly.
  4.  
  5. Remove the 4 spark plug boots and retainers from the coil housing cover.
  6.  
  7. Install the 4 standard spark plug wires onto the housing spark contacts.
  8.  
  9. Install the other ends of the spark plug wires onto the corresponding spark plugs.
  10.  
  11. Place the transaxle in P , engage the emergency brake, then start the engine and let it idle.
  12.  
  13. Using a spark plug wire removing tool, preferably the plier-type, carefully remove the boot from one of the cylinders.
  14.  
  15. The engine will sputter, run worse, and possibly nearly stall. If this happens reinstall the plug wire and move to the next cylinder. If the engine runs no differently, or the difference is minimal, shut the engine off and inspect the spark plug wire, spark plug, and if necessary, perform component diagnostics as covered in this section. Perform the test on all cylinders to verify the which cylinders are suspect.
  16.  

3.1L Engine
  1. Place the transaxle in P , engage the emergency brake, then start the engine and let it idle.
  2.  
  3. Using a spark plug wire removing tool, preferably, the plier-type, carefully remove the boot from one of the cylinders.
  4.  
  5. The engine will sputter, run worse, and possibly nearly stall. If this happens reinstall the plug wire and move to the next cylinder. If the engine runs no differently, or the difference is minimal, shut the engine off and inspect the spark plug wire, spark plug, and if necessary, perform component diagnostics as covered in this section. Perform the test on all cylinders to verify the which cylinders are suspect.
  6.  

 
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