INTRODUCTION
The following diagnostic steps will help prevent overlooking a simple problem. This is also where to begin diagnosis for a no-start condition.
The first step in diagnosing any driveability problem is verifying the customer's complaint with a test drive (if possible) under the conditions the problem reportedly occurred.
Before entering self-diagnostics, perform a careful and complete visual inspection. Most engine control problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. Before condemning the computerized system, perform each test listed in this article.
Note. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure.
VISUAL INSPECTION
Visually inspect all electrical wiring, looking for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and are not pinched or cut. Inspect air induction system for possible vacuum leaks.
Compression
| WARNING | DO NOT use ignition switch during compression tests on fuel injected vehicles. Use a remote starter switch to crank engine. Fuel injectors and fuel pump are activated by ignition switch during cranking mode, which can create a fire hazard or contaminate the engine oiling system. |
Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer user manual for specific instructions. On Range Rover, engine compression ratio specification is displayed above engine identification code. Engine identification code is stamped on a cast pad located between cylinders No. 3 and No. 5. (Scheme 1)
On all models, start and run engine until normal engine operating temperature is reached. Remove all spark plugs. Disable ignition system. Insert compression gauge, with Wide Open Throttle (WOT) and a fully charged battery, crank engine using a remote starter switch until reading stabilizes. Compression specifications are not supplied by manufacturer. Difference between cylinders must not exceed 25 percent.
Scheme 1
Exhaust System Backpressure
The exhaust system can be checked with a vacuum or pressure gauge. If using a pressure gauge, remove front HO2S and connect a 0-5 psi pressure gauge. Start engine and run at 2500 RPM. If exhaust system backpressure is greater than 2 psi, exhaust system or catalytic converter is plugged.
If using a vacuum gauge, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Open throttle part way and hold steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for a restriction.
FUEL PRESSURE
| WARNING | System may contain fuel pressure even when engine has not been run for awhile. Always relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
| WARNING | During fuel pressure release, fuel leakage is inevitable. Take necessary precautions in case of fire. Wear safety glasses during procedure. |
Relieving Fuel Pressure
- Freelander Turn ignition off. Locate Schrader valve on fuel rail, above accumulator. Remove Schrader valve cap. Place a shop towel under Schrader valve. Cover Schrader valve with a shop rag. Open Schrader valve to release fuel pressure.
- Discovery Turn ignition off. Locate Schrader valve on fuel rail. Remove Schrader valve cap. Place a shop towel under Schrader valve. Cover Schrader valve with a shop rag. Open Schrader valve to release fuel pressure.
- Range Rover Turn ignition off. Fuel pressure can be relieved at fuel feed fitting at fuel rail. Position cloth around fitting to catch fuel spray. Using 2 wrenches, loosen fitting, allowing fuel system to depressurize.
Regulated Fuel Pressure
All injectors are fed from a common fuel rail as part of a returnless fuel system. Fuel pressure is maintained at 51 psi (3.5 bar) by a regulator that is integral with the fuel pump.
FUEL INJECTOR RESISTANCE
| Application | Ohms @ 68°F (20°C) |
|---|---|
| Discovery & Range Rover | 13.8-15.2 |
| Freelander | 13-16 |
FUEL INJECTOR RESISTANCE
IGNITION CHECKS
Note. On Freelander, left (front) cylinders have spark plug wires. On right (rear) cylinders, ignition coils are mounted directly onto spark plugs.
SPARK
Check for spark at each spark plug wire using a high output spark tester. Check suspect spark plug wires for fraying, chafing, deterioration and/or opens. Specific resistance for each wire is not available from manufacturer.
IGNITION COIL RESISTANCE
| Application | Primary | Secondary |
|---|---|---|
| Except Freelander | 0.45-0.55 Ohms | 12,000-14,600 Ohms |
| Freelander | (1) | (1) |
| (1) Information is not available from manufacturer. | ||
| (1) | Information is not available from manufacturer. |
IGNITION COIL RESISTANCE - Ohms @ 68°F (20°C)
IDLE SPEED & MIXTURE
Note. Before checking idle speed and mixture ensure air and fuel filters are okay. Check vacuum pipes and hoses for correct routing, leaks and/or restriction. Check ignition system for poor connections or loose wires. Perform repairs as necessary.
BASE IDLE SPEED
Base idle speed is not adjustable. If base idle speed is suspected of being out of specification, verify throttle cable adjustment. See CABLE ADJUSTMENT in ON-VEHICLE ADJUSTMENTS article. If throttle cable adjustment is okay, see appropriate SELF-DIAGNOSTICS ARTICLE. For computer controlled idle speed specifications, see IDLE SPEED SPECIFICATIONS table.
| Application | Specification | |
|---|---|---|
| Idle Speed (1) | ||
| Discovery | 610-710 RPM | |
| Freelander | 650-800 RPM | |
| Range Rover | 660 RPM | |
| (1) Idle speed is controlled by ECM. Specification is in Neutral with accessories off. | ||
| (1) | Idle speed is controlled by ECM. Specification is in Neutral with accessories off. |
IDLE SPEED SPECIFICATIONS
IDLE MIXTURE
Note. On Discovery and Range Rover, idle mixture is controlled by Bosch Motronic 5.2.1 engine management system through the ECM. On Freelander, idle mixture is controlled by Siemens MS43 engine management system through the ECM. On all models, mixture is not adjustable, but should be checked as part of normal tune-up procedure using an exhaust gas analyzer. If mixture is not within specifications, see appropriate SELF-DIAGNOSTICS article. Always refer to SERVICE INFORMATION underhood label in engine compartment. If underhood label and MITCHELL(R) specifications differ, always use underhood label specifications.
| Application | Specification | |
|---|---|---|
| CO @ Idle (1) | ||
| Discovery | 0.5% Or Less | |
| Freelander | (2) | |
| Range Rover | (2) | |
| (1) Idle mixture is not adjustable. (2) Information is not available. | ||
| (1) | Idle mixture is not adjustable. |
| (2) | Information is not available. |
IDLE MIXTURE SPECIFICATIONS
IGNITION TIMING
On Discovery and Range Rover, ignition timing is controlled by Bosch Motronic M5.2.1 engine management system through the ECM and is not adjustable.
| Application | Specification |
|---|---|
| Discovery & Range Rover | (2) 12°BTDC @ Idle |
| Freelander | (3) |
| (1) Idle speed and timing are computer controlled and are not adjustable. (2) Expected value of ignition timing at normal operating temperature. (3) Information is not available. | |
| (1) | Idle speed and timing are computer controlled and are not adjustable. |
| (2) | Expected value of ignition timing at normal operating temperature. |
| (3) | Information is not available. |
IGNITION TIMING (Degrees BTDC) (1)
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES , proceed to appropriate SELF-DIAGNOSTICS article. If no hard codes are found in self-diagnostics, (if vehicle has self-diagnostic system) proceed to TROUBLE SHOOTING - NO CODES article for diagnosis by symptom (i.e., ROUGH IDLE, NO START, etc.) or intermittent diagnostic procedures.
See also:
• BASIC DIAGNOSTIC PROCEDURES