Passing your MoT Emissions Test

Introduction

Passing ones MoT emissions test with ones Elise appears to be an annual trauma. This page is the beginnings of a 'how-to' guide of hints and tips to help you through.

A Brief Overview of Emissions Control

Combustion engines of all types generally burn hydrocarbons (HC)as their primary fuel source.

In the limiting case, hydrocarbons combine with ambient oxygen (O2) to create carbon dioxide (CO2) and water (H2O), however an internal combustion engine is never 100% efficient and this chemical reaction usually has some incomplete products, namely carbon monoxide (CO) and unburned hydrocarbons (uHC).

In addition, the normally inert nitrogen (N2) in the air forms oxides of nitrogen (NOx) during the high temperature and pressure phases of the combustion process.

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The Lambda Sensor

Otherwise known as an Oxygen Sensor or a HEGO sensor (Heated Exhaust Gas Oxygen), the Lambda sensor returns a voltage signal which is a non-linear function of the amount of oxygen present in the exhaust