Exhaust Values - Information

Introduction

In a perfect combustion, water and carbon dioxide are produced.

The only catch is that there is no perfect combustion in an internal combustion engine.

Therefore, "by-products" are formed such as hydrocarbons, carbon monoxide, oxygen, carbon dioxide, nitrogen, and water. These five are described below (we will skip water).

HC (Hydrocarbons = Fuel)

Hydrocarbons are unburned fuel. If you have issues with spark plugs, ignition cables, or any misconfigured ignition, or vacuum leaks, the level of hydrocarbons (HC) in the exhaust system will increase.

Causes

• Poor ignition system
• Bad ignition cables
• Bad spark plugs
• Vacuum leaks / air leaks
• Incorrect engine tuning

CO (Carbon Monoxide)

CO is the result of a too rich mixture (under lambda 1) where combustion cannot occur properly due to a lack of oxygen. A tuned engine is often set to inject more fuel "than necessary" for better cylinder cooling at higher RPMs / high combustion pressures (increased safety margin). This should not affect HC at idle during a measurement; if it does, then something is wrong.

Causes

• Low idle
• Rich mixture (under lambda 1)
• Clogged air filter / airways
• Clogged crankcase ventilation
• Incorrect engine tuning

O2 (Oxygen)

Vacuum leaks, exhaust leaks, or ignition problems often result in readings on an O2 measurement, and all can lead to suspicions.

O2 should be at 1.5% or less during measurement if CO2 is 14-15% and HC and CO are approximately 0.

CO2 (Carbon Dioxide)

Carbon dioxide is a measure of how efficient the combustion is. A larger amount of CO2 in the exhaust gases means that the engine is operating efficiently.

CO2 should ideally be at 13-15% during measurement if CO and HC are approximately 0 and O2 is 1-3%.

NOx (Nitrogen Oxides)

NOx is formed when the combustion temperature exceeds approximately 1370 degrees. This does not affect engine performance more than the smoke that can form when NOx and HC mix.

Causes:

• High temperature