Engine Controls - On-Vehicle Adjustments Land Rover Discovery L318

ENGINE MECHANICAL

Before performing any on-vehicle adjustments to fuel or ignition systems, ensure engine mechanical condition is okay.

VALVE CLEARANCE

Note. All models use hydraulic lifters. No adjustments are required.

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 specifications differ, always use underhood label specifications.

IGNITION TIMING (1)

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 appropriate SELF-DIAGNOSTICS article. Always refer to SERVICE INFORMATION underhood label in engine compartment. If underhood label and specifications differ, always use underhood label specifications.

IDLE SPEED & MIXTURE SPECIFICATIONS

See appropriate CRUISE CONTROL SYSTEMS article in ACCESSORIES & EQUIPMENT for Discovery Series I cruise control linkage adjustments.

Discovery Series II

Ensure throttle cable is properly adjusted before attempting to adjust cruise control linkage. See THROTTLE CABLE ADJUSTMENT. Loosen outer cable locknuts. Adjust rear cable locknut until distance "A" between cruise control cable lever and throttle cable driven lever is 0.019-0.060" (0.5-1.5 mm). (Scheme 1) Tighten cable front locknut and recheck distance "A" measurement.

Range Rover

Ensure throttle cable is properly adjusted before attempting to adjust cruise control linkage. See THROTTLE CABLE ADJUSTMENT. Push cruise control linkage towards plenum chamber to remove all free play from cruise control cable. Check that distance "A" between cruise control cable lever and throttle cable driven lever is 0.019-0.060" (0.5-1.5 mm). (Scheme 1) If necessary, rotate cruise control cable adjusting thumbwheel until distance "A" is as specified. (Scheme 2)

Scheme 1

Scheme 2

KICKDOWN CABLE ADJUSTMENT

Note. On Discovery Series II and Range Rover, kickdown is electronically controlled.

1. Disconnect kickdown cable and throttle cable from kickdown linkage. Loosen kickdown cable locknuts. Adjust kickdown cable until end of cable sleeve is distance "A" from support bracket. (Scheme 3) Distance "A" should be 1.1" (28 mm). When cable is in correct position, there should be 6 threads of cable sleeve exposed at rear of bracket, distance "B". Tighten both kickdown cable locknuts and connect cable to kickdown linkage. Ensure kickdown cable adjustment position is correct.
2. Connect throttle cable to kickdown linkage. Pull rubber boot on kickdown cable back to expose crimped collar on cable. Turn plastic adjustment nut on throttle cable until crimped collar on kickdown cable is 0.04" (1.0 mm) from end of kickdown outer cable, distance "C". (Scheme 3) Reposition rubber boot.
3. Ensure throttle valve is fully closed. Loosen locknut on kickdown cable at engine compartment support bracket. Turn kickdown cable adjustment locknut until clearance between outer cable end and crimped collar on inner cable is 0.01-0.05" (0.25-1.25 mm). Tighten locknuts, rotate throttle linkage and ensure clearance is correct.

Scheme 3

Loosen throttle cable thumb-wheel. (Scheme 4) Ensure throttle linkage is against stop and throttle valve is in a fully closed position. Rotate thumb-wheel clockwise until throttle linkage is about to lift from stop (slack is removed from cable). Rotate thumb-wheel 1/4 turn counterclockwise. Fully depress accelerator pedal to ensure throttle valve opens fully. Check cruise control adjustment.

Scheme 4

Loosen throttle cable locknuts. (Scheme 1) Adjust rear locknut until it is in contact with back of bracket and throttle lever is in contact with inner driven lever. Ensure that driven lever remains in contact with throttle stop screw, (throttle closed). Tighten cable front nut to lock cable to bracket. Move throttle from closed position and ensure driven lever is in contact with throttle stop screw when throttle is closed.

See also:
• THROTTLE CABLE ADJUSTMENT