Engine Controls - Tests W/o Codes Toyota 4Runner II

INTRODUCTION

Before diagnosing symptoms or intermittent faults, perform steps in BASIC DIAGNOSTIC PROCEDURES and SELF-DIAGNOSTICS articles. Use this article to diagnose driveability problems existing when a hard fault code is not present.

Note. Some driveability problems may have been corrected by manufacturer with a revised computer calibration chip or computer control unit. Check with manufacturer for latest chip or computer application.

Symptom checks can direct the technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific component, a system test or an adjustment.

Use intermittent test procedures to locate driveability problems that DO NOT occur when the vehicle is being tested. These test procedures should also be used if a soft (intermittent) trouble code was present, but no problem was found during self-diagnostic testing.

This article covers 2 trouble shooting areas

1. Symptom Diagnosis
2. Intermittents

Note. For specific testing procedures, see I - SYS/COMP TESTS article in the ENGINE PERFORMANCE Section. For specifications, see ADJUSTMENTS or SPECIFICATIONS article in the ENGINE PERFORMANCE Section.

SYMPTOM DIAGNOSIS

Symptom checks cannot be used properly unless the problem occurs while the vehicle is being tested. To reduce diagnostic time, ensure steps in BASIC DIAGNOSTIC PROCEDURES and SELF-DIAGNOSTICS articles were performed before diagnosing a symptom. Symptoms available for diagnosis include

1. Difficult To Start/No Start (Engine Will Not Crank Or Cranks Slowly)
2. Difficult To Start/No Start (Cranks Okay)
3. Engine Stalls Often
4. Engine Stalls Sometimes
5. Rough Idle/Missing
6. High Idle Speed (No Drop)
7. Engine Backfires (Lean Fuel Mixture)
8. Muffler Explosion (Rich Fuel Mixture)
9. Engine Hesitates/Poor Acceleration

DIFFICULT TO START/NO START (WON'T CRANK OR CRANKS SLOWLY)

1. Check battery and cables, charging system and fusible links.
2. Check ignition switch.
3. Check starter relay.
4. Check clutch start switch (M/T) or neutral start switch (A/T).
5. Check starter and wiring connections.

DIFFICULT TO START/NO START (CRANKS OKAY)

1. Check for vacuum leaks (oil filler cap, oil dipstick, hose connections, PCV valve and hose).
2. Verify secondary ignition system performance.
3. Check cam position sensor (if equipped).
4. Ensure ignition timing is correct.
5. Check auxiliary air valve (if equipped).
6. Ensure fuel system (pump, lines, filter and pressure regulator) performs properly.
7. Verify proper compression and valve clearance.
8. Check circuit opening relay.
9. If engine starts with accelerator pedal depressed, check idle speed control valve (if equipped) and wiring connection.
10. Check fuel pump switch in airflow meter.
11. Check wiring connection to ECU.
12. Check power to ECU via fusible links, fuses and EFI main relay.
13. Check airflow meter, coolant temperature sensor and air temperature sensor.
14. Check injection signal circuit.

ENGINE STALLS OFTEN

1. Check for vacuum leaks (oil filler cap, oil dipstick, hose connections, PCV valve and hose).
2. Ensure fuel system (pump, lines, filter and pressure regulator) performs properly.
3. Check air filter.
4. Check idle speed and ensure ignition timing is correct.
5. Verify secondary ignition system performance.
6. Verify proper compression and valve clearance.
7. Check cold start injector and cold start injector time switch.
8. Check auxiliary air valve (if equipped) or idle speed control valve (if equipped).
9. Check circuit opening relay.
10. Check fuel injectors.
11. Check power to ECU via fusible links, fuses and EFI main relay.
12. Check airflow meter, coolant temperature sensor and air temperature sensor.
13. Check injection signal circuit.

ENGINE STALLS SOMETIMES

1. Check airflow meter and connectors.
2. Check EFI main relay, circuit opening relay and connectors. Check for slight change in engine idle when connector or relay are slightly tapped or wiggled.

ROUGH IDLE/MISSING

1. Check for vacuum leaks (oil filler cap, oil dipstick, hose connections, PCV valve and hose).
2. Check air filter.
3. Check idle speed and ensure ignition timing is correct.
4. Verify secondary ignition system performance.
5. Verify proper compression and valve clearance.
6. Check variable induction system (if equipped).
7. Check cold start injector and cold start injector time switch.
8. Ensure fuel system (pump, lines, filter and pressure regulator) performs properly.
9. Check fuel injectors.
10. Check power to ECU via fusible links, fuses and EFI main relay.
11. Check airflow meter, coolant temperature sensor and air temperature sensor.
12. Check injection signal circuit.
13. Check O2 sensor(s).

HIGH IDLE SPEED (NO DROP)

1. Check accelerator linkage.
2. Check power steering idle-up circuit (if equipped).
3. Check A/C idle-up circuit (if equipped).
4. Check idle speed control valve (if equipped) or auxiliary air valve (if equipped) and wiring.
5. Check variable induction system (if equipped).
6. Ensure ignition timing is correct.
7. Check throttle position sensor.
8. Check for high fuel pressure.
9. Check for leakage at cold start injector or fuel injectors.
10. Check power to ECU via fusible links, fuses and EFI main relay.
11. Check airflow meter, coolant temperature sensor and air temperature sensor.
12. Check injection signal circuit.

ENGINE BACKFIRES (LEAN FUEL MIXTURE)

1. Check for vacuum leaks (oil filler cap, oil dipstick, hose connections, PCV valve and hose).
2. Check idle speed and ensure ignition timing is correct.
3. Check cold start injector and cold start injector time switch.
4. Ensure fuel system (pump, lines, filter and pressure regulator) performs properly.
5. Check for clogged fuel injectors.
6. Check power to ECU via fusible links, fuses and EFI main relay.
7. Check airflow meter, coolant temperature sensor, throttle position sensor and air temperature sensor.
8. Check injection signal circuit.
9. Check O2 sensor(s).

MUFFLER EXPLOSION (RICH FUEL MIXTURE)

1. Check idle speed and ensure ignition timing is correct.
2. Check cold start injector and cold start injector time switch.
3. Ensure fuel system (pump, lines, filter and pressure regulator) performs properly.
4. Check for fuel injector leakage.
5. Verify secondary ignition system performance.
6. Verify proper compression and valve clearance.
7. Check throttle position sensor, injection signal circuit and O2 sensor(s).
8. Check for exhaust system leaks.

ENGINE HESITATES/POOR ACCELERATION

1. Check for clutch slipping or brakes dragging.
2. Check for vacuum leaks (oil filler cap, oil dipstick, hose connections, PCV valve and hose).
3. Check air filter.
4. Check for leakage or clogging between air filter and turbocharger inlet and between turbocharger outlet and cylinder head (if equipped).
5. Verify secondary ignition system performance and timing.
6. Verify proper compression and valve clearance.
7. Ensure fuel system (pump, lines, filter and pressure regulator) performs properly.
8. Check for clogged fuel injectors.
9. Check variable induction system (if equipped).
10. Check power to ECU via fusible links, fuses and EFI main relay.
11. Check airflow meter, coolant temperature sensor, air temperature sensor and throttle position sensor.
12. Check injection signal circuit.

INTERMITTENT PROBLEM DIAGNOSIS

Intermittent fault testing requires duplicating circuit or component failure to identify the problem. These procedures may lead to the computer setting a fault code, which may help in diagnosis.

If problem vehicle does not produce fault codes, monitor voltage or resistance values using a DVOM while attempting to reproduce conditions causing intermittent fault. A status change on DVOM indicates a fault has been located.

Use a DVOM to pinpoint faults. When monitoring voltage, ensure ignition switch is in ON position or engine is running. Ensure ignition switch is in OFF position or negative battery cable is disconnected when monitoring circuit resistance. Status changes on DVOM during test procedures indicate area of fault.

Intermittent Simulation

To reproduce the conditions creating an intermittent fault, use the following methods

1. Lightly vibrate component. See VIBRATION METHOD.
2. Heat component. See HEAT METHOD.
3. Wiggle or bend wiring harness. See VIBRATION METHOD.
4. Spray component with light water mist or radiator with water. See HUMIDTY METHOD.
5. Remove/apply vacuum source.

Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. Use test results to identify a faulty component or circuit.

Wiring Harness Testing

If vibration is suspected as cause of an intermittent, lightly shake wiring harness vertically and horizontally while monitoring suspected circuit or component with a DVOM. Look for a voltage fluctuation during this test procedure. Inspect connector joint, fulcrum of the vibration and body through-portion. (Scheme 116)

Component & Sensor Testing

Lightly vibrate suspect component, relay or sensor, while monitoring suspected circuit or component with a DVOM. Look for a voltage fluctuation during this test procedure. (Scheme 116)

Electrical Connector Testing

Lightly shake connector vertically and horizontally, while monitoring suspected circuit or component with a DVOM. Look for a voltage fluctuation during this test procedure. Visually inspect connector and repair as required.

Scheme 116

HEAT METHOD

Apply heat to a suspected component with a hair dryer or similar device and monitor suspected circuit or component with a DVOM.

HUMIDITY METHOD

If humidity or moisture are suspected of causing an intermittent failure, spray water on the radiator to increase humidity in the engine compartment. Check if a malfunction occurs by monitoring the suspected circuit or component with a DVOM.

If a vehicle is subject to water leakage, the admitted water may contaminate the ECU. When testing a vehicle where water leakage has occurred, carefully inspect the ECU terminals for corrosion. Repair or replace the ECU connectors as required.

ELECTRICAL LOAD METHOD

To check if an intermittent occurs under electrical load, turn on all electrical loads (heater blower, headlights, rear window defogger, wipers, etc.). Check if the malfunction occurs by monitoring the suspected circuit or component with a DVOM.