If the emission levels on a 4-gas analyzer indicate that both CO and HC are high and both O₂ and CO₂ are low, what could this indicate?

Question

Quizplus · Accepted Answer

High CO and HC levels typically indicate a rich fuel mixture, as there is too much fuel and not enough oxygen for complete combustion. The low oxygen sensor (O2) readings reinforce this, as they would be expected to read low in a rich condition due to the lack of oxygen.

If the Emission Levels on a 4-Gas Analyzer Indicate That