Engine Controls - Trouble Shooting Land Rover Discovery L318

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 Electronic Control Module (ECM) or Land Rover PROM. Check with manufacturer for latest ECM application.

Symptom checks can direct the technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific component, 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 an intermittent trouble code was present, but no problem was found during self-diagnostic testing. See INTERMITTENT PROBLEM DIAGNOSIS .

Note. For specific testing procedures, see SYSTEM & COMPONENT TESTING article. For specifications, see ON-VEHICLE ADJUSTMENTS or SERVICE & ADJUSTMENT SPECIFICATIONS article.

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 appropriate SELF-DIAGNOSTICS article were performed before diagnosing a symptom. Symptom checks are listed in order of probability, ease of accomplishment, and accessibility. Symptoms available for diagnosis are as follows

1. Engine Hard To Start (Turns Over)
2. Engine Does Not Start (Does Not Turn Over)
3. Engine Hesitates Or Misses
4. Engine Knock
5. Loss Of Power
6. Poor Fuel Mileage
7. Rough Or Unstable Idle

ENGINE DOES NOT START (DOES NOT TURN OVER)

Check for security system malfunction (if equipped).

1. Check battery and cables, charging system and fusible links.
2. Starter motor inoperative.
3. Check engine ground straps.
4. Faulty ignition switch.
5. Faulty Park/Neutral position switch.
6. Park/Neutral position switch misaligned or out of position.

ENGINE HARD TO START (ENGINE TURNS OVER)

Check battery and cables, charging system and fusible links.

1. Low battery charge.
2. Check Crankshaft Position (CKP) sensor for correct installation.
3. Check clutch start switch (M/T) or Neutral start switch (A/T) for proper position and adjustment.
4. Check fuel level and ensure fuel is not contaminated.
5. Check Idle Air Control (IAC) valve.
6. Check main relay and fuel pump relay.
7. Check ignition switch sense signal.
8. Check ignition switch.
9. Check inertia fuel shut-off switch and ensure switch is closed.
10. Check starter relay.
11. Check starter and wiring connections.

ENGINE HESITATES OR MISSES

Check for vacuum leaks.

1. Check air filter.
2. Verify secondary ignition system performance.
3. Verify proper compression and valve clearance.
4. Check ignition coils.
5. Check operation of injectors.
6. Check vehicle speed sensor.

ENGINE KNOCK

Blown head gasket.

1. Incorrect valve timing.
2. Lean fuel mixture.
3. Low coolant in radiator/engine (engine overheating).
4. Check installation of knock sensors.
5. Stuck thermostat (engine overheating).
6. Wrong octane fuel.

LOSS OF POWER

Burnt or sticking valves.

1. Ensure engine compression is okay.
2. Fuel system malfunction.
3. Incorrect camshaft timing.
4. Incorrect valve clearance.
5. Ignition system malfunction.
6. Wrong octane fuel.

POOR FUEL MILEAGE

Check for vacuum leaks.

1. Check air filter.
2. Check idle speed and ensure base timing is correct.
3. Verify secondary ignition system performance.
4. Verify proper compression and valve clearance.

ROUGH OR UNSTABLE IDLE

Check for vacuum leaks.

1. Check air filter.
2. Check Idle Air Control (IAC) valve.
3. Check idle speed and ensure base timing is correct.
4. Verify secondary ignition system performance.
5. Verify proper compression and valve clearance.

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 (on some systems) which may help in diagnosis.

If problem vehicle does not produce fault codes, monitor voltage or resistance values using a Land Rover TestBook, an OBD-II scan tool or a DVOM while attempting to reproduce conditions causing intermittent fault. A status change indicates a fault has been located.

Use a Land Rover TestBook, an OBD-II scan tool or 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 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.
2. Heat component to normal operating temperature.
3. Wiggle or bend wiring harness.
4. Spray component with a water mist.
5. Remove/apply vacuum source. Monitor circuit/component voltage or resistance while simulating intermittent. If engine is running, monitor for self-diagnostic codes. See appropriate SELF-DIAGNOSTICS article. Use test results to identify a faulty component or circuit.

See also:
• INTERMITTENT PROBLEM DIAGNOSIS