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Engine Controls - Basic Diagnostic Procedures - 2.2L: Diagnosis Pontiac Sunfire I

Testing & Diagnostics ~890 words

VISUAL INSPECTION

Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. If necessary, see VACUUM DIAGRAMS - ALERO & GRAND AM or VACUUM DIAGRAMS - CAVALIER & SUNFIRE article to verify routing and connections. Inspect air induction system for possible vacuum leaks.

MECHANICAL INSPECTION

WARNINGBecause fuel injectors on many models are triggered by ignition switch during cranking mode, Do NOT use ignition switch during compression tests. Use a remote starter to crank engine to prevent fire hazard or engine oiling system contamination.

Cylinder Leakage Test

CAUTIONBefore servicing any electrical component, the ignition key must be in the OFF or LOCK position and all electrical loads must be OFF, unless instructed otherwise in these procedures. If a tool or equipment could easily come in contact with a live exposed electrical terminal, also disconnect the negative battery cable. Failure to follow these precautions may cause personal injury and/or damage to the vehicle or its components.

A leakage test may be performed in order to measure cylinder/combustion chamber leakage. High leakage may indicate one or more of the following

  1. Worn or burnt valves.
  2. Broken valve springs.
  3. Stuck valve lifters.
  4. Incorrect valve lash/adjustment.
  5. Damaged piston.
  6. Worn piston rings.
  7. Worn or scored cylinder bore.
  8. Damaged cylinder head gasket.
  9. Cracked or damaged cylinder head.
  10. Cracked or damaged engine block.
  1. Disconnect the battery ground negative cable.
  2. Remove the spark plugs.
  3. Rotate the crankshaft to place the piston in the cylinder being tested at Top Dead Center (TDC) of the compression stroke.
  4. Install the Cylinder Head Leakdown Tester (J 35667-A), or equivalent.
  5. Apply shop air pressure to the cylinder head leakdown tester and adjust according to the manufacturers instructions.
  6. Record the cylinder leakage value. Cylinder leakage that exceeds 25 percent in considered excessive and may require component service. In excessive leakage situations, inspect for the following conditions: Air leakage sounds at the throttle body or air inlet hose that may indicate a worn or burnt intake valve or a broken valve spring. Air leakage sounds at the exhaust system tailpipe that may indicate a worn or burnt exhaust valve or a broken valve spring. Air leakage sounds from the crankcase, oil level indicator tube, or oil fill tube that may indicate worn piston rings, a damaged piston, a worn or scored cylinder bore, a damaged engine block or a damaged cylinder head. Air bubbles in the cooling system may indicate a damaged cylinder head or a damaged cylinder head gasket.
  7. Perform the leakage test on the remaining cylinders and record the values.

NO-START DIAGNOSIS

Note. For circuit identification, see WIRING DIAGRAMS .

Note. Some vehicles are equipped with anti-theft systems (VATS or PASS-Key®) which will not allow vehicle to be started if improper starting procedures or improperly coded ignition keys are used. Both fuel injection and cranking systems will be disabled. Loss of fuel enable signal from anti-theft decoder module should set a diagnostic trouble code in PCM memory.

Note. For terminal and circuit identification, see CONNECTOR IDENTIFICATION in SELF-DIAGNOSTICS - 2.2L ALERO, CAVALIER, GRAND AM & SUNFIRE - GASOLINE article.

  1. Definition A no-start is defined as engine cranks properly, but does not start. Engine may fire a few times.

FUEL PRESSURE TEST

Manufacturer does not provide testing procedures for many individual systems and components. For information on testing fuel system, see FUEL SYSTEM DIAGNOSIS (GASOLINE) or FUEL SYSTEM DIAGNOSIS (CNG) .

ELECTRONIC IGNITION SYSTEM DIAGNOSIS WITHOUT SPECIAL TOOL

For circuit identification, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS in SELF-DIAGNOSTICS - 2.2L ALERO, CAVALIER, GRAND AM & SUNFIRE - GASOLINE article. For connector terminal identification, see CONNECTOR IDENTIFICATION in SELF-DIAGNOSTICS - 2.2L ALERO, CAVALIER, GRAND AM & SUNFIRE - GASOLINE article.

Diagnostic Aids

  1. A small amount of resistance in the battery positive voltage circuit to the PCM may cause a no start. Test the battery positive voltage circuit for excessive resistance or corrosion.
  2. The PCM grounds will cause a no start only if none of them are making a good connection.
  3. If the Crankshaft Position (CKP) sensor is loose the sensor may cause an intermittent no start by moving away from the reluctor wheel.

ELECTRONIC IGNITION SYSTEM DIAGNOSIS WITH SPECIAL TOOL

For circuit identification, see WIRING DIAGRAMS . For component locations, see COMPONENT LOCATIONS in SELF-DIAGNOSTICS - 2.2L ALERO, CAVALIER, GRAND AM & SUNFIRE - GASOLINE article. For connector terminal identification, see CONNECTOR IDENTIFICATION in SELF-DIAGNOSTICS - 2.2L ALERO, CAVALIER, GRAND AM & SUNFIRE - GASOLINE article.

Circuit Description

Each ignition coil supplies secondary voltage to a pair of spark plugs. This is called a waste spark ignition system. The Powertrain Control Module (PCM) supplies Ignition Control (IC) signals to the Ignition Control Module (ICM). The ICM fires the correct ignition coil at the correct time based on the IC signals. The ICM detects if cylinder 1 or cylinder 3 is on the compression stroke by sensing the secondary voltage and polarity of each side of the ignition coil. The ICM detects this voltage with sensing circuitry integrated into each ignition coil. The higher voltage is on the compressing cylinder. The ICM provides a synthesized cam signal to the PCM based on these inputs. This is called compression sense ignition. The PCM uses the cam signals to synchronize fuel injection.

This system consists of the following circuits

  1. Ignition 1 voltage.
  2. Ground.
  3. Camshaft Position (CMP) sensor signal.
  4. IC timing control - 2/3.
  5. IC timing control - 1/4.
  1. A small amount of resistance in the battery positive voltage circuit to the PCM may cause a no start. Test the battery positive voltage circuit for excessive resistance or corrosion.
  2. The PCM grounds will cause a no start only if none of them are making a good connection.
  3. If the Crankshaft Position (CKP) sensor is loose the sensor may cause an intermittent no start by moving away from the reluctor wheel.

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