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's oiling system. |
Check engine mechanical condition with a compression gauge, vacuum gauge, or an engine analyzer. See engine analyzer user manual for specific instructions. 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 34)
Start and operate engine until normal engine operating temperature thermostat opens. Remove all spark plugs. Disconnect ignition coil connector. Insert compression gauge, crank engine using a remote starter switch until reading stabilizes. With Wide Open Throttle (WOT) and fully charged battery compression should be approximately 170-180 psi (12.0-12.7 kg/cm 2 ).
Scheme 34
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 | On Discovery Series I, fuel pressure can exceed 35 psi (2.5 kg/cm 2 ), even when engine has not been run for awhile. On Discovery Series II and Range Rover, fuel pressure can exceed 50 psi (3.5 kg/cm 2 ), even when engine has not been run for awhile. On all models, always relieve fuel pressure before disconnecting any fuel injection-related component. DO NOT allow fuel to contact engine or electrical components. |
Note. On Discovery Series I, fuel pressure may be measured at fuel rail or fuel filter fittings. On Discovery Series II and Range Rover, a fuel pressure test point is provided by means of a Schrader valve positioned between rear of engine and firewall, above ignition coil packs.
Relieving Fuel Pressure
Turn ignition off. Disconnect negative battery terminal and then positive battery terminal. Connect Land Rover TestBook to vehicle and depressurize fuel system. Position shop towel around appropriate fitting to protect against fuel spray. Carefully loosen appropriate fitting. When fuel pressure has been released, tighten fitting.
Regulated Fuel Pressure
There are 8 fuel injectors, one per cylinder which the ECM operates sequentially. On Discovery Series I, regulated fuel pressure should be 35-37 psi (2.5-2.6 kg/cm 2 ) and varies depending on amount of intake manifold vacuum acting on fuel pressure regulator. On Discovery Series II and Range Rover, all 8 injectors are fed from a common fuel rail as part of a returnless fuel system. Fuel pressure is maintained at a approximately 50-52 psi (3.5-3.6 kg/cm 2 ) by a regulator that is integral with the fuel pump.
FUEL INJECTOR RESISTANCE
| Application | Ohms |
|---|---|
| Discovery Series I | 15.7-16.7 |
| Discovery Series II & Range Rover | 13.8-15.2 |
FUEL INJECTOR RESISTANCE
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
Remove primary and secondary leads from ignition coils. Using ohmmeter, check resistance of primary coils and secondary coils between positive and negative terminals of each coil. See IGNITION COIL RESISTANCE table. Replace faulty coil if resistance is not as specified.
| Application | Primary | Secondary |
|---|---|---|
| Discovery Series I | 0.80 | 13,000 |
| Discovery Series II | 0.45-0.55 | 12,000-14,600 |
| Range Rover | 0.45-0.55 | 12,000-14,600 |
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.
Discovery Series I
Check base idle speed using a Land Rover TestBook. Ensure Idle Air Control (IAC) valve is set to 20-25 steps at idle. Ensure Mass Airflow (MAF) sensor output voltage is approximately 1.4 volts at idle. If necessary to adjust idle speed, locate by-pass screw in plenum chamber. Using a self-tapping screw, remove tamper-proof plug covering by-pass screw. Use TestBook to monitor idle speed while turning by-pass screw. Ensure there are no loads, the transmission is in Park or Neutral and air suspension (if equipped) is in standard position and disabled. Install NEW tamper-proof plug over by-pass screw after rechecking idle speed.
Discovery Series II & Range Rover
Base idle speed is not adjustable. Check base idle using a Land Rover TestBook.
IDLE MIXTURE
Note. On Discovery Series I, idle mixture is controlled by GEMS through the ECM. On Discovery Series II and Range Rover, idle mixture is controlled by Bosch Motronic M5.2.1 engine management system through the ECM. Mixture is not adjustable, but should be checked as part of normal tune-up procedure using an exhaust gas analyzer. If vehicle is not within specifications, see SELF-DIAGNOSTICS article. Always refer to SERVICE INFORMATION underhood label in engine compartment. If underhood label and MITCHELL® specifications differ, always use underhood label specifications. See IDLE SPEED & MIXTURE SPECIFICATIONS table.
| Application | Specification | ||
|---|---|---|---|
| Base Idle Speed (1) | |||
| Discovery Series I | |||
| In Neutral With A/C Off | 597-653 | ||
| In Neutral With A/C On | 672-728 | ||
| Discovery Series II (2) | 610-710 RPM | ||
| Range Rover (2) | 660 RPM | ||
| CO @ Idle | |||
| Range Rover | (3) | ||
| Discovery Series I & II | Less Than 0.5% | ||
| (1) Idle speed is controlled by ECM through Idle Air Control (IAC) valve. With engine at normal operating temperature, IAC valve should be set to 20-25 steps. (2) In Neutral with A/C off. (3) Information not available from manufacturer. | |||
| (1) | Idle speed is controlled by ECM through Idle Air Control (IAC) valve. With engine at normal operating temperature, IAC valve should be set to 20-25 steps. |
| (2) | In Neutral with A/C off. |
| (3) | Information not available from manufacturer. |
IDLE SPEED & MIXTURE SPECIFICATIONS
IGNITION TIMING
Note. On Discovery Series I, ignition timing is controlled by Land Rover's Generic Engine Management System (GEMS) through the Engine Control Module (ECM) and is not adjustable. On Discovery Series II and Range Rover, ignition timing is controlled by Bosch Motronic M5.2.1 engine management system through the ECM and is not adjustable. Ignition timing is adjusted for each cylinder based on engine load, speed and temperature, knock control, automatic gearbox shift control and idle speed control. On Range Rover, nominal value for a warm engine at idle is 12° BTDC. Always refer to SERVICE INFORMATION underhood label in engine compartment. If underhood label and MITCHELL® specifications differ, always use underhood label specifications.
| Application | Specification |
|---|---|
| Discovery Series I | (2) |
| Discovery Series II | (2) |
| Range Rover | 12° BTDC |
| (1) Idle speed and timing are computer controlled and are not adjustable. (2) Information not available from manufacturer. | |
| (1) | Idle speed and timing are computer controlled and are not adjustable. |
| (2) | Information not available from manufacturer. |
IGNITION TIMING (1)
SUMMARY
If no faults were found while performing BASIC DIAGNOSTIC PROCEDURES, proceed to 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.