- Symptoms - Engine Controls

SYMPTOMS - COMPUTERS AND CONTROL SYSTEMS

SYMPTOMS DESCRIPTION
Symptoms cover conditions that are not covered DTCs. Certain conditions can cause multiple symptoms. These conditions are listed together under Symptoms Testing. Conditions that may only cause certain symptoms are listed separately under Additional Symptoms Test. Perform the Symptoms Testing before using the Additional Symptoms Tests. Poor Fuel Fill Quality test may be performed separately from the Symptoms Testing and Additional Symptoms Tests procedures.

DIAGNOSTIC FAULT INFORMATION
Perform the Diagnostic System Check - Vehicle before using the symptoms procedures. Testing and Inspection

SYMPTOMS DEFINITION

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 occurs 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.

SYMPTOMS VERIFICATION
Verify that all of 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 the normal operating range.
- Bulletins are not available for the current symptom.
- The ECM grounds are clean, tight, and in the correct locations.
- The vehicle tires are correctly inflated and meet original equipment specifications.
- The air filter element is not restricted. Refer to Air Cleaner Element Replacement.

SYMPTOMS TESTING
Backfire, Cuts Out/Misses, Detonation/Spark Knock, Dieseling/Run-On, Hard Start, Hesitation/Sag/Stumble, Lack of Power/Sluggishness/Sponginess, Poor Fuel Economy, Rough, Unstable, or Incorrect Idle and Stalling, or Surges/Chuggles
1. Test for the following conditions:
- The fuel system for the following:
- Correct fuel pressure-Refer to Fuel System Diagnosis. Component Tests and General Diagnostics
- Fuel injectors that are leaking or improper operation-Refer to Fuel Injector Coil Test. Fuel Injector Coil Test
- Contaminated or a poor fuel quality condition-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) Alcohol/Contaminants-in-Fuel Diagnosis (w/Special tool). Without Special Tool With Special Tool
- The ignition system for the following:
- Spark plugs for incorrect heat range or an abnormal condition-Refer to Spark Plug Inspection. Testing and Inspection
- For diagnosis of coolant or oil fouled spark plugs, refer to Loss of Coolant or Symptoms - Engine. Loss of Coolant Symptom Related Diagnostic Procedures
- 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.
- Weak spark using the J 26792 Spark Tester-Refer to Electronic Ignition (EI) System Diagnosis. Electronic Ignition (EI) System Diagnosis
- The operation of the transmission torque converter clutch (TCC)-The scan tool should indicate an engine speed drop when the TCC is commanded ON. Refer to Symptoms - Automatic Transmission.
- The operation of the A/C compressor
- Items that can cause an engine to run lean or rich-Refer to DTC P0171, P0172, P2187, or P2188. P0171 P0172 P2187 P2188
- 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 460-620 ohms.
- The engine for the following mechanical failures-Refer to Symptoms - Engine:
- Excessive oil in the combustion chamber or leaking valve seals
- Incorrect cylinder compression
- Sticking or leaking valves
- Worn camshaft lobes
- Incorrect valve timing
- Worn rocker arms
- Broken valve springs
- Excessive carbon buildup in the combustion chambers-Clean the chambers with top engine cleaner. Follow the instructions on the can.
- Incorrect engine parts Symptom Related Diagnostic Procedures
- Vacuum hoses for splits or kinks-Verify that the routing and connections are as shown on the Vehicle Emission Control Information label.
- Knock sensor (KS) system for excessive spark retard activity-Refer to Knock Sensor (KS) System Description and DTC P0325. P0325
- The exhaust system components for the following:
- Physical damage or possible internal failure
- The three-way catalytic converters for a restriction For more information, refer to Symptoms - Exhaust System. Symptom Related Diagnostic Procedures
- Electromagnetic interference (EMI) on the reference circuit can cause a misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase in the engine speed parameter with little change in actual engine speed indicates that EMI is present. Inspect the high voltage components near the ignition control circuit if a condition exists.
- Inspect the positive crankcase ventilation (PCV) system and all connections for leaks or restrictions.
- Evaporative emission (EVAP) canister purge solenoid that is stuck open
- The engine cooling system for the following conditions:
- The thermostat is the correct heat range-Refer to Thermostat Diagnosis. Symptom Related Diagnostic Procedures
- Proper engine coolant level-Refer to Draining and Filling Cooling System.
2. If the above conditions do not address the symptom, refer to the additional symptoms tests.

ADDITIONAL SYMPTOMS TESTS

Detonation/Spark Knock
Test the engine for an overheating condition. Refer to Symptoms - Cooling System. Symptom Related Diagnostic Procedures

Lack of Power, Hesitation, or Cut Out
Test for the correct operation of the intake manifold tuning valve (IMTV) system. Refer to Intake Manifold Tuning (IMT) Valve Diagnosis. Intake Manifold Tuning (IMT) Valve Diagnosis

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.

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 RTV sealant. The sensors may have a white powdery coating and result 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 condition.

Hard Start
- 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 � 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 vs 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.
- Test the idle air control (IAC) system. Refer to DTC P0506 or P0507. P0506 P0507
- Test the fuel pump relay operation. The fuel pump should turn ON for 2 seconds when the ignition is turned ON. Refer to Fuel Pump Electrical Circuit Diagnosis. Component Tests and General Diagnostics

Hesitation, Sag, Stumble
- Test the manifold absolute pressure (MAP) sensor. Refer to DTC P0106. P0106
- Test the generator. Refer to Symptoms - Starting and Charging. Repair the charging system if the generator output voltage is less than 9 volts or more than 16 volts. Symptom Related Diagnostic Procedures

Poor Fuel Economy
- Heavy loads being carried or towed
- Acceleration rate too much or too often
- 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.

Poor Fuel Fill Quality
Test for the following conditions that are applicable to the current symptom:

Difficult to fill
- Restricted vent lines
- The EVAP vent valve is stuck closed.
- High fuel temperature
- A condition with the internal components of the fuel tank assembly.

Fuel Odor
- Saturated EVAP canister
- A condition with the internal components of the fuel tank assembly