Symptoms - Engine Controls
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Symptoms - Engine Controls
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The symptom comprises conditions not covered by diagnostic trouble codes (DTC). Some conditions can cause several 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.
Backfire
Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
Cuts Out, Misses
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.
Detonation/Spark Knock
A mild to severe ping which usually gets worse while under acceleration. The engine makes sharp metallic knocks that change with throttle opening.
Dieseling, Run-On
Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
Hard Start
Engine cranks OK, but does not start for a long time. The vehicle does eventually run, or may start but immediately stalls.
Hesitation, Sag, Stumble
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 severe conditions.
Lack of Power, Sluggishness, or Sponginess
The engine delivers less than expected power. Little or no increase in 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.
Poor Fuel Fill Quality
Difficulty when refueling the vehicle.
Rough, Unstable, or Incorrect Idle and Stalling
The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. Engine idle may vary in speed. Either condition may be severe enough to stall the engine.
Surges/Chuggles
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.
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The engine control module (ECM) and the malfunction indicator lamp (MIL) are operating correctly.
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There are no DTCs stored.
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The scan tool data is within the normal operating range.
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Bulletins are not available for the current symptom.
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The ECM grounds are clean, tight, and in the correct locations.
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The vehicle tires are correctly inflated and meet original equipment specifications.
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The air filter element is not restricted.
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Test for the following conditions:
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For the correct installation of the Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor
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The fuel system for the following:
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The ignition system for the following:
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For diagnosis of coolant or oil fouled spark plugs
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Wet down the secondary ignition system with water from a spray bottle. Wetting down the secondary ignition system may help locate damaged or deteriorated components. Look/listen for arcing or misfiring as the water is applied.
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The operation of the transmission torque converter clutch (TCC). The scan tool should indicate an engine speed drop when the TCC is commanded ON.
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The operation of the A/C compressor
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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 700-1 200 Ω.
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Excessive oil in the combustion chamber or leaking valve seals
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Incorrect cylinder compression
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Sticking or leaking valves
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Excessive carbon buildup in the combustion chambers. Clean the chambers with top engine cleaner. Follow the instructions on the can.
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Vacuum hoses for splits or kinks. Verify that the routing and connections are as shown on the vehicle emission control information label.
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Fuel octane switch setting. Verify the fuel octane switch is set to the proper fuel octane rating for the fuel being used in the vehicle.
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Turbocharger system for proper operation, if equipped
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Turbocharger charge air cooler system has no leaks, if equipped
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The exhaust system components for the following:
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Physical damage or possible internal malfunction
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Electromagnetic interference on the reference circuit can cause a misfire condition. You can usually detect electromagnetic interference with a scan tool. Monitor the engine speed parameter. A sudden increase in the engine speed parameter with little change in actual engine speed indicates that electromagnetic interference is present. Inspect the high voltage components near the ignition control circuit if a condition exists.
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Inspect the positive crankcase ventilation system and all connections for leaks or restrictions.
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Evaporative Emission (EVAP) Canister Purge Solenoid Valve that is stuck open
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The engine cooling system for the following conditions:
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If the above conditions do not address the symptom, refer to the additional symptoms tests.
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Additional Symptoms Tests
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Detonation/Spark Knock
Test the engine for an overheating condition. Refer to
Symptoms - Engine Cooling
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Poor Fuel Economy
Inspect for foreign material accumulation in the throttle bore, and for carbon deposits on the throttle plate and shaft. Also inspect for throttle body tampering.
Rough, Unstable, or Incorrect Idle and Stalling
Inspect the engine mounts.
Engine Mount Replacement
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Surges/Chuggles
Test the heated oxygen sensors (HO2S). The HO2S should respond quickly to a change in throttle position. If the HO2S do not respond to different throttle positions, inspect for contamination from fuel, silicon, or the incorrect use of room temperature vulcanizing sealant. The sensors may have a white powdery coating that results in a high – but false – signal voltage, which gives a rich exhaust indication. The ECM reduces the amount of fuel delivered to the engine, causing a driveability problem.
Hard Start
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Test the engine coolant temperature (ECT) sensor. Compare the ECT sensor value to the intake air temperature (IAT) sensor value on a cold engine. The ECT and IAT sensor values should be within about 3°C (5°F). If the ECT sensor is out of range with the IAT sensor, test the resistance of the ECT sensor. Refer to
Temperature Versus Resistance
for resistance specifications. Replace the ECT sensor if the resistance is not within specification. If the sensor is within the specification, test the ECT circuits for a high resistance.
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Hesitation, Sag, Stumble
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Test the generator. Refer to
Symptoms - Engine Electrical
. Repair the charging system if the generator output voltage is less than 9 V or more than 16 V.
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Poor Fuel Economy
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Heavy loads being carried or towed
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Acceleration rate too much or too often
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Inspect for foreign material accumulation in the throttle bore, and for carbon deposits on the throttle plate and shaft. Also inspect for throttle body tampering.
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Difficult to fill
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A condition with the internal components of the fuel tank assembly
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For more information, refer to the following:
Fuel Odor
