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Symptoms Testing

Cuts Out/Misses, Hard Start, Hesitation/Sag/Stumble, Lack of Power/Sluggishness/Sponginess, Poor Fuel Economy, Rough, Unstable, or Incorrect Idle and Stalling, Fuel Knock/Combustion Noise, Surges/Chuggles, or Excessive Smoke - Black, White, Gray, or Blue

  1. Test for the following conditions:
    • The sensor systems for the following:
      • Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .
      • Test for an intermittent FRP sensor signal by wiggling the harness between the sensor and the ECM with the ignition ON and the engine OFF, while monitoring the parameter with a scan tool.
      • Inspect for an intermittent crankshaft position (CKP) sensor signal.
      • Test the crankshaft position (CKP) sensor for the correct resistance. The CKP sensor resistance may be out of range after a hot soak. The resistance should be between 774-946 ohms.
      • Inspect the engine coolant temperature (ECT) sensor. Use the scan tool in order to compare the ECT with the intake air temperature (IAT) sensor on a cold engine. The ECT should be within 3°C (5°F) of the IAT. If not within the specified range, inspect for a high resistance in the coolant sensor circuit or the sensor.
    • The Fuel System for the following:
      • Inspect for external fuel leaks.
      • Inspect for low fuel pressure. Refer to Fuel System Diagnosis .
      • Inspect the fuel system for a plugged fuel filter or air in the fuel system. Refer to Fuel System Diagnosis .
      • Inspect the fuel supply to the fuel injection pump. Refer to Fuel System Diagnosis .
      • Inspect the fuel tank cap vent for proper operation.
      • Inspect the fuel quality. Refer to Contaminants-in-Fuel Diagnosis .
      • Observe the actual verses desired fuel rail pressure with a scan tool, with the engine idling.
      • If the ECM or a fuel injector has recently been replaced, it may be necessary to confirm the fuel injector flow rate values. Refer to Fuel Injector Flow Rate Programming .
      • Inspect for restricted or plugged fuel injectors. Refer to Fuel Injector Balance Test with Tech 2 .
      • Inspect for a sticking Fuel Pressure Regulator. The symptom for this condition will be an idle surge of at least 100 RPM. This surge will be from 50 RPM above Desired Idle Speed to 50 RPM below Desired Idle Speed.
    • Engine mechanical for the following.
      • Improper valve timing
      • Worn rocker arms
      • Low engine compression-Refer to Engine Compression Test .
      • Broken or weak valve springs
      • Worn camshaft lobes
      • Excessive oil in the combustion chamber-Leaking valve seals
  2. If the above conditions do not address the symptom, refer to the additional symptoms tests.
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