Bulkhead Workshop › Land Rover models › Land Rover Discovery 1 3.5 / 3.9 / 4.0 V8 › Workshop guide › Plugs, leads & ignition timing

Land Rover Discovery 1 3.5 / 3.9 / 4.0 V8: plugs, leads & ignition timing

Ignition · Discovery 1 (1989–98) · 1989–1998

How often: every 12,000 mi or year, whichever comes first. Eight plugs and long HT leads: misfires on a V8 are easy to miss until fuel use climbs.

Work safely: support the vehicle on axle stands, never a jack alone; let it cool first. Check figures against your workshop manual. You do this work at your own risk.

Parts

• 8 × Spark plugs (Champion RN9YC type (ERR743) on 3.5; check the handbook for the 3.9/4.0, gap 0.72–0.88 mm) ERR743
• Distributor cap & rotor or coil packs (if worn)

Tools

• Plug socket with extension
• Code reader
• Multimeter

Step by step

1. Remove and check plugs one at a time so the HT leads stay in the right order.
2. Gap or renew plugs (Champion RN9YC type (ERR743) on 3.5; check the handbook for the 3.9/4.0, gap 0.72–0.88 mm). Check each lead (or coil pack boot) for cracks and resistance.
3. Distributor engines (14CUX): check the cap and rotor for cracks and tracking. Coil-pack engines (GEMS / Bosch): the timing is set by the ECU; read any misfire codes instead.

More Land Rover Discovery 1 3.5 / 3.9 / 4.0 V8 servicing