In our July ’14 issue, (page 82) we published a technical feature about a problematic ’06 Discovery 3. The Landy was on its third turbo, with just 90 000 km on the clock! What’s more, the vehicle would frequently revert to limp mode when driven past 120 km/h, or when placed under load − towing a trailer or caravan.
After conducting research on the subject, we came to the likely conclusion that the Landy’s catalytic converter was to blame. Just to recap: a vehicle’s catalytic converter is designed to reduce pollution before it’s emitted into the atmosphere. It does this by converting noxious gases into less harmful ones by channeling the gases through a platinum-coated honeycomb. Unfortunately, this honeycomb structure has a finite life and eventually clogs up with soot, or carbon deposits. In our Disco 3’s case, the catalytic converter was roughly 50% blocked.
As a result, the choked-up system was causing a pressure build-up within the exhaust pipe − between the turbo and the cat. The increase in exhaust pressure was resulting in heat build-up, and pressure on the exhaust impeller. To make matters worse, the blown turbo would then spray engine oil on the catalytic converter’s honeycomb, thus causing even more carbon deposits, and further blockage issues.