For 1990-2009 cars

### 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 consists of diagnosing faults not covered by diagnostic trouble codes. Certain conditions can cause multiple symptoms. These conditions are list together in the Symptoms Tests. Conditions that only cause certain symptoms are listed separately in Additional Symptoms Tests. Perform the Symptoms Tests before using the Additional Symptoms Tests.

### Symptoms Definition

Backfire: Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
Cut, Misfire: 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: The engine continues to run after the ignition is turned OFF, but runs very rough.
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 can result in engine lack of power under more of these conditions: Lack of Power, Sluggishness or Sponginess, 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.
Rough, Unstable, or Incorrect Idle and Stalling: Engine operating unsteady 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.
Surge: 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

Perform the following checks before using the symptom tables:

• | Ensure the engine control module (ECM) and the malfunction indicator lamp (MIL) are operating correctly.

• | Make sure there are no Diagnostic Trouble Codes (DTC) stored.

• | Make sure the scan tool data is within the normal operating range. Refer to Scan Tool Data List .

• | Verify Customer Concern.

• | Perform visual/physical checks in this section. Perform visual/physical checks is very important, other tests fixed condition may not need. It can assist to reveal an intermittent malfunction.

#### Identifying Intermittent Conditions

Many intermittent conditions occur with harness connector movement caused by vibration, engine torque, rough pavement, or component operation. Refer to the following items lists that may cause an intermittent conditions:

• | Moisture, connector, terminal and component entry of water.

• | Incompatible mating of the Connector

• | Poor Terminal Connection

• | Excessive Circuit or component resistance - excessive resistance contains all resistance, whatever the resistance value is, and will cause component operation stop.

• | Harnesses too Short or Overtighten.

• | The wire's insulation is cut or disconnected.

• | The ambient temperature is too high or too low

• | ECT is too High or too Low

• | Underhood Temperature too High

• | Due to Poor Connections of Circuit Resistance, Terminal or Electrical Load too High, Component or Connector too Hot

• | The system voltage is too high or too low

• | Vehicle Load is too heavy

• | Rough Road

• | Form Relay, Solenoids or other electrical surge EMI/Circuit Interference

• | Incorrect installation of aftermarket accessory equipment

#### Visual/Physical Inspection

• | Make sure the Engine Control Module grounds for being clean, tight, and in the correct locations. Refer to Power and Grounding Schematic Legend and Power and Grounding Connector End Views .

• | Make sure vacuum hoses that are split, kinked, or improperly connected. Refer to Evaporative Emissions Hose Routing Diagram .

• | Make sure the air filter is clean and free from obstruction.

• | Make sure there is no water intrusion in connector terminal and component.

• | Inspect the air intake duct for the following:

- | Collapsed

- | Damaged areas

- | Looseness

- | Improper installation

- | Leaking

• | Inspect the throttle body mounting area, Mass Air Flow (MAF) and the intake manifold sealing surfaces for air leaks.

• | Inspect the harness for the following conditions:

- | Poor connection

- | Clamp

- | Cut

• | Inspect for loose, damaged, improperly positioned or missing sensors/components.

• | Check terminals for corrosion or poor connection.

### Symptoms Tests

Backfire, cut/misfire, Detonation/Spark Knock, Dieseling, Hard Start, Hesitation/Sag/Stumble, Lack of Power/Sluggishness/Sponginess, Poor fuel economy, Rough, Unstable, Incorrect Idle or Stalling.

• | Test the fuel system for the following conditions:

- | If fuel system volumetric and pressure is correct, refer to Fuel System Diagnosis .

- | Injector for proper installation. Refer to Fuel Injector Diagnosis .

- | Fuel Quality condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Test the ignition system for the following conditions:

- | The proper operation of the ignition system--Refer to Electronic Ignition (EI) System Diagnosis .

- | Spark Plug--Refer to Spark Plug Inspection .

- | Park Plug proper application--Refer to Ignition System Specifications .

• | Inspect for the following conditions:

- | Correct operation of the transmission torque converter clutch (TCC). The scan tool should indicate an engine speed drop when the TCC is commanded ON.

- | The air conditioning compressor operates correctly.

- | Items that can cause an engine to run lean or rich. Refer to D DTC P0171, P0172, P0174, or P0175 .

- | Crankshaft Position (CKP) Sensor operates properly

- | Knock Sensor (KS) System operates properly

- | Inspect the exhaust system. Refer to Symptoms - Engine Exhaust .

- | Electromagnetic Interference (EMI) on the reference circuit can cause 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 for high voltage components near the ignition control circuits if a condition exists.

- | The crankcase ventilation valve operates correctly.

- | Check the throttle body for clean. The throttle body plate may cause a symptoms. Refer to Throttle Body Inspection and Cleaning .

- | The EVAP canister purge solenoid valve operates correctly.

- | Engine cooling operates normally--refer to Symptoms - Engine Cooling

• | Inspect the engine for the following mechanical conditions:

| Refer to Symptoms - Engine Mechanical .

- | Excessive oil in the combustion chamber or leaking valve seals

- | Oil Consumption

- | Incorrect cylinder compression

- | Sticking or leaking valves

- | Worn camshaft lobes

- | Improper valve timing

- | Worn rocker arms

- | Broken valve springs

- | Excessive carbon buildup in the combustion chambers--Clean the chambers using top engine cleaner. Follow the instructions on the can.

- | Incorrect engine parts

• | If the above conditions do not involve the symptom, refer to the Additional Symptoms Tests.

### Additional Symptoms Tests

#### Hard Starting

• | Verify that the Engine Coolant Temperature (ECT) sensor is not changed in value. Refer to Temperature Versus Resistance .

• | Make sure the Engine Electrical is operating normally. Refer to Symptoms - Engine Electrical .

• | Verify that the driver is using the correct starting procedure as described in the owners manual.

• | Verify that there is sufficient fuel.

• | Inspect for excessive crankshaft endplay that will cause the crankshaft position (CKP) sensor reluctor wheel to move out of alignment with the CKP sensor. Refer to Crankshaft and Bearing Cleaning and Inspection .

#### Hesitation, Sag, Stumble

• | Inspect the mass air flow (MAF) sensor for obstructed, contamination and damage. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .

• | Test the generator. Refer to Symptoms - Engine Mechanical . Repair the charging system if the generator output voltage is less than 9 volts or more than 16 volts.

• | Inspect for excessive crankshaft endplay that will cause the crankshaft position (CKP) sensor reluctor wheel to move out of alignment with the CKP sensor. Refer to Crankshaft and Bearing Cleaning and Inspection .

#### Poor Fuel Economy

• | Heavy loads being carried or towed

• | Acceleration rate too much or too often

• | Inspect the brake system for brake drag.

• | Inspect for proper operation of the speedometer.

• | Verify that the Engine Coolant Temperature (ECT) sensor is not changed in value. Refer to Temperature Versus Resistance .

• | Inspect the mass air flow (MAF) sensor for obstructed, contamination and damage. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .

• | 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. Refer to Throttle Body Inspection and Cleaning .

#### Detonation/Spark Knock

• | Test the engine for an overheating condition. Refer to Symptoms - Engine Cooling .

• | Verify that the Engine Coolant Temperature (ECT) sensor is not changed in value. Refer to Temperature Versus Resistance .

• | If there are no engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicles minimum octane requirements.

#### Lack of Power, Sluggishness, or Sponginess

• | Check the engine electrical system for normal operation. Refer to Symptoms - Engine Mechanical .

• | Verify that each injector harness is connected to the correct injector or cylinder.

• | Inspect the mass air flow (MAF) sensor for obstructed, contamination and damage. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .

#### Rough, Unstable, or Incorrect Idle and Stalling

• | Inspect the mass air flow (MAF) sensor for obstructed, contamination and damage. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .

• | Inspect the engine mounts.

• | Inspect intake and exhaust manifolds for casting flash.

#### Surges/Chuggles

• | Inspect the mass air flow (MAF) sensor for obstructed, contamination and damage. Refer to Mass Airflow Sensor/Intake Air Temperature Sensor Replacement .

• | Test the heated oxygen sensors (HO2S). The HO2S should respond quickly to a change in throttle position. If the HO2S does 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.

• | Verify that each injector harness is connected to the correct injector .