What Causes Black or Yellow Discoloration on the Exhaust Pipe?

[McParker]

Black or yellow discoloration on the exhaust pipe is primarily caused by incomplete combustion inside the vehicle's engine. Unburned oil vapors passing through the catalytic converter can partially carbonize, and over time, these carbon deposits accumulate at the exhaust pipe outlet, leading to blackening. The reasons for incomplete combustion are as follows: 1. Poor spark plug performance, resulting in incomplete fuel combustion in the cylinder. Solution: Repair or replace the spark plugs. 2. Incorrect ignition timing, causing the engine to malfunction. Solution: Adjust the ignition timing. 3. Poor driving habits during startup, insufficient cylinder pressure, or excessively low engine temperature. Solution: Adjust driving habits.