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Home >> GMC >> 1991 >> Value Van 7.4 N >> Repair and Diagnosis >> External Pages >> Different car >> Section 31 (Engine Controls - Tests W/Codes - 3.3L CNG) >> Self-Diagnostic Tests >> Test NTC-16A - Performing No DTC Mechanical Test

Test NTC-16A - Performing No DTC Mechanical Test

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  1. Engine controller systems are operating properly and are not cause of driveability problem. Perform following additional checks to assist in identifying a possible mechanical problem:
    • Engine vacuum (must be at least 13 in. Hg in Neutral).
    • Engine valve timing (must be within specification).
    • Engine compression (must be within specification).
    • Engine exhaust system (must be free of restrictions).
    • Engine PCV system (must flow freely).
    • Engine drive sprocket (must be properly positioned).
    • Torque converter stall speed (must be within specification).
    • Power brake booster (must be free of internal vacuum leaks).
    • Fuel (must be free of contamination).
    • Fuel injector (check for plugged or restricted injector or control wire not connected to correct injector).
  2. If a rich or lean condition of oxygen sensor has brought you to TEST NTC-16A, and one of above items is not cause of rich or lean condition, replace Powertrain Control Module (PCM). Perform TEST VER-2.
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