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Symptoms - Engine Controls

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    • Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Symptoms Description

Symptoms covers conditions that are not covered by DTCs. Certain conditions can cause multiple symptoms. These conditions are listed together under Symptoms Testing. Conditions that may only cause specific symptoms are listed separately under Additional Symptoms Testing. Perform the Symptoms Testing before using the Additional Symptoms Testing.

Symptoms Definition

Cuts Out, Misfires: A steady pulsation or jerking that follows engine speed, which is usually more pronounced as the engine load increases. This condition is not normally felt above 1 500 RPM or 48 km/h (30 MPH). The exhaust has a steady spitting sound at idle or at low speed.

Hard Start: The engine cranks OK, but does not start for a long time. The vehicle does eventually run, or may start but immediately stall.

Hesitation, Sag, Stumble: A momentary lack of response as the accelerator is pushed down. This condition can occur at any vehicle speed. This condition is usually more pronounced when first trying to make the vehicle move, as from a stop. This condition may cause the engine to stall in critical conditions.

Lack of Power, Sluggishness, or Sponginess: The engine delivers less than expected power. Little or no increase in vehicle speed when the accelerator pedal is pushed down part way.

Poor Fuel Economy:  Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, the fuel economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test.

Rough, Unstable, or Incorrect Idle and Stalling: The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. Engine idle speed may vary. Either condition may be critical enough to stall the engine.

Surges/Chuggles: An engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the accelerator pedal position.

Fuel Knock/Combustion Noise: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with the throttle opening.

Excessive Smoke (Black): Black smoke under load, idle or start up, hot or cold.

Excessive Smoke (White): White smoke under load, idle or start up, hot or cold.

Excessive Smoke (Grey or Blue): Grey or Blue smoke under load, idle or start up, hot or cold.

Reference Information

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Symptoms Verification

Verify the following conditions are true:

    • The engine control module (ECM) and the malfunction indicator lamp (MIL) are operating correctly.
    • There are no diagnostic trouble codes (DTCs) stored.
    • The scan tool data is within a normal operating range.
    • The fuel system is not leaking.
    • Air is not entering the fuel system.
    • The air filter element is not restricted.
    • The vehicle tyres are correctly inflated and meet original equipment specifications.

Symptoms Testing

Cuts Out/Misfires, 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, Grey, or Blue

  1. Test for the following conditions:
    2. • The sensor systems for the following:
       - Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage.
       - Test for an intermittent fuel rail pressure 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 sensor signal.
       - Test the crankshaft position sensor for the correct resistance. The crankshaft position sensor resistance may be out of range after a hot soak. The resistance should be between 774-946 Ω.
       - Inspect the engine coolant temperature (ECT) sensor. Use the scan tool in order to compare the ECT with the inlet 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.
       - 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
       - Broken or weak valve springs
       - Worn camshaft lobes
       - Excessive amount of oil in the combustion chamber - Leaking valve seals
  2. If the above conditions do not address the symptom, refer to the additional symptoms tests.

Additional Symptoms Tests

Hard Start

    • Verify the ECT has not shifted in value. Refer to Temperature Versus Resistance : Exhaust Temperature Sensor  → ECT and IAT Sensor .
    • Inspect for a slow cranking speed. Refer to Symptoms - Engine Electrical .
    • Verify the engine electrical system for correct operation. Refer to Symptoms - Engine Electrical .
    • Verify the driver is using the correct starting procedure as described in the owners manual.
    • Inspect for a restriction in turbocharger inlet duct.
    • Inspect for the correct operation of the fuel heater.
    • Inspect for a restriction or a leak in the inlet manifold.
    • Inspect the exhaust system for a possible restriction. Refer to Restricted Exhaust : Diesel .
    • Inspect for excessive crankshaft end play that will cause the crankshaft position sensor reluctor wheel to move out of alignment with the crankshaft position sensor.

Hesitation, Sag, Stumble

    • Test the generator. Refer to Symptoms - Engine Electrical . Repair the charging system if the generator output voltage is less than 9 V or greater than 16 V.
    • Inspect for excessive crankshaft end play that will cause the crankshaft position sensor reluctor wheel to move out of alignment with the crankshaft position sensor.

Poor Fuel Economy

    • Heavy loads being carried or towed
    • Acceleration rate too much or too often
    • Inspect the brake system for brake drag.
    • Inspect the tyres for the correct air pressure.
    • Inspect for incorrect operation of the speedometer.
    • Inspect for an air leak in the charge air cooler.
    • Inspect the air conditioning system for proper operation.
    • Suggest to the owner to fill the fuel tank and inspect the fuel economy.
    • Suggest to the driver to read the Important Facts on Fuel Economy in the Owner Manual.
    • Verify the ECT has not shifted in value. Refer to Temperature Versus Resistance : Exhaust Temperature Sensor  → ECT and IAT Sensor .

Lack of Power, Hesitation, or Cut Out

    • Inspect the engine electrical system for correct operation. Refer to Symptoms - Engine Electrical .
    • Compare the vehicle with a similar module. Ensure the vehicle has an actual malfunction.
    • Inspect for a proper transmission operation.
    • Inspect the engine oil level and quality.
    • Inspect for an air leak in the charge air cooler.
    • Inspect for a worn or damaged turbo charger turbine wheel, shaft or compressor wheel.
    • Inspect for a restricted or plugged exhaust.
    • Inspect for a restriction in the charge air cooler.
    • Inspect for a skewed mass air flow (MAF) sensor.
    • Inspect that the exhaust gas recirculation (EGR) valve is fully closing.
    • Ensure that the EGR valve does not bind when manually moving the valve.
    • Inspect the torque converter clutch (TCC) operation.
    • Inspect the air conditioning system for the correct operation.

Rough, Unstable, or Incorrect Idle and Stalling

    • Inspect the engine mounts.
    • Inspect the inlet and exhaust manifolds for casting flash.
    • The exhaust system for damaged or collapsed pipes
    • The exhaust manifold for a collapsed inner wall
    • The mufflers for heat distress or possible internal malfunction
    • Inspect the park neutral position switch circuit.

Surges/Chuggles

    • Ensure the driver understands the torque converter clutch (TCC) operation.
    • Ensure the driver understands the A/C compressor operation.
    • Use the scan tool to ensure the vehicle speed sensor (VSS) reading matches the speedometer.

Fuel Knock/Combustion Noise

    • Inspect for obvious overheating malfunctions. Refer to Engine Overheating .
    • Inspect for a low engine coolant level.
    • Inspect for any restricted air flow through the radiator.
    • Inspect for a malfunctioning or incorrect thermostat.
    • Inspect for a correct coolant solution. The solution should be a 50/50 mix of anti-freeze and water.

Excessive Smoke (Black)

Normal Operation

    • During light to moderate acceleration there should be no black smoke.
    • During the 2-3 hard accelerations after normal light load driving there may be some black smoke momentarily but should not last for greater than 5 s.
    • During hard acceleration there may always be a very faint puff of black smoke.

Abnormal Operation

    • Black smoke during light to moderate acceleration.
    • Heavy black smoke during hard acceleration that lasts for greater than 5 s.
    • Heavy black smoke during every hard acceleration and/or during transmission shift transitions
    • Inspect for an air leak in the charge air cooler or the air ducts between the turbocharger and the inlet manifold.
    • Inspect for a restriction in the turbocharger charge air cooler.
    • Inspect for a restriction in the inlet manifold.
    • Inspect that the EGR valve is fully closing. Remove the EGR valve and visually inspect that there is no light seen between the valves and the valve seats.
    • Ensure that the EGR valve does not bind when manually moving the valve.
    • Inspect for excessive oil entering the combustion chamber.

Excessive Smoke (White or Grey)
    • Inspect the coolant level in the reservoir. White coolant smoke may be mistaken for blue/grey smoke. If the coolant level is low, refer to Loss of Coolant .
    • If excessive smoke is present, inspect for a stuck open fuel injector by performing the following procedure:
        1. Disconnect the electrical connector at the fuel injection pump.
        2. Remove the glow plugs. Refer to Glow Plug Replacement .

        Note: Do not stand in front of the glow plug holes while cranking the engine.

        3. Crank the engine while observing the glow plug holes for fuel spray.
        4. Replace the fuel injectors for the cylinders that spray fuel.
        5. Inspect for contaminated oil or high oil level.
    • 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 the fuel injectors. Refer to Fuel Injector Replacement .
   


© Copyright Chevrolet. All rights reserved
   


© Copyright Chevrolet. All rights reserved