If the catalytic converter is gutted, which emission changes are expected?

• A. HC and CO would be elevated; CO2 would be higher than normal; O2 would be lower.
• B. HC would increase while CO would decrease.
• C. HC and CO would be elevated; CO2 would be lower than normal; O2 would be slightly higher.
• D. HC would decrease; CO would increase.

Answer: (C)

When the catalytic converter is gutted, the exhaust can no longer undergo the oxidation reactions that the converter normally performs. The converter’s job is to help oxidize carbon monoxide (CO) to carbon dioxide (CO2) and hydrocarbons (HC) to CO2 and water (H2O), using available oxygen in the exhaust. Without those catalytic reactions, less CO and HC are converted, so they appear in higher amounts in the exhaust.

Because these oxidation processes aren’t happening as efficiently, the total CO2 produced from those oxidations drops, so CO2 levels in the exhaust are lower than normal. Additionally, since fewer reactions consume oxygen, the oxygen content in the exhaust is slightly higher.

So the expected changes are elevated HC and CO, lower CO2, and slightly higher O2 in the exhaust.