LEMON Manuals: Even more car manuals for everyone
Home >> GMC >> 1983 >> Magnavan 6.2 J, 475/M40 >> Repair and Diagnosis >> Engine Performance >> System >> Feedback Carburetor Component Test >> Driver Comment Checks >> Engine Performance Problem - Odor, Surge, Fuel Economy Or Emission Problem

Engine Performance Problem - Odor, Surge, Fuel Economy Or Emission Problem

  1. If the "CHECK ENGINE" light is not on, normal checks that would be performed on cars without the system should be done first.
  2. If the alternator or coolant light is on with the "CHECK ENGINE" light, they should be diagnosed first.
  3. Inspect for poor connections at coolant sensor, mixture control solenoid, etc. Also check for poor or loose vacuum hoses and connections. Repair as necessary.
  4. If there is an intermittent "CHECK ENGINE" light, but no trouble code is stored, check the following:
    • Check for intermittent connection in circuit between ignition coil to ground.
    • Check for arcing at spark plug wires or spark plugs.
    • Check battery to ECM terminals "C" and "R".
    • Check ECM Terminals "A" and "U" to engine ground.
    • Check for loss of trouble code long-term memory: Grounding dwell lead for 10 seconds with "TEST" lead ungrounded should produce a Code 23 which should be retained after the engine is turned off and the ignition switch is turned to "RUN" position. If a Code 23 is not displayed, ECM is defective and must be replaced.
    • Ensure that the EST wires are kept away from the spark plug wires, distributor housing, ignition coil and alternator. Wires from ECM Terminal No. 13 to distributor and the shield (if used) should have a good ground.
  5. If the customer is complaining of stalling, rough idle, dieseling or improper idle speed, see IDLE SPEED CONTROL CHECK.
  6. If the complaint is detonation (spark knock) check the following items:
    • Check the ESC system. Refer to ESC SYSTEM CHECK.
    • Check the MAP or Vacuum Sensor output. See CHART 7 - MAP & BARO OUTPUT CHECK or CHART 8 - VACUUM SENSOR CHECK.
    • Check EGR system. Refer to EGR VALVE CHECK.
    • Check TPS enrichment system operation. See TPS ENRICHMENT CHECK.
    • Check HEI operation. Refer to appropriate IGNITION SYSTEM article in the ELECTRICAL section.
  7. If the complaint is poor performance and/or poor fuel economy, check the following:
    • Perform appropriate EST PERFORMANCE CHECK.
    • Perform ESC SYSTEM CHECK.
  8. If the customer is experiencing poor full throttle performance, refer to CRANKS, BUT WON'T RUN chart.
  9. If the complaint is intermittent no starts, make the following checks:
    • Check for incorrect pick-up coil or ignition coil. See CRANKS, BUT WON'T RUN chart.
    • Check for intermittent ground connection on ECM.
scientia non olet · About LEMON Manuals