Exhaust Backpressure

Catalytic converters, particulate filters and silencers all add some backpressure. Blockages raise it sharply. Turbo diesel engines are sensitive to high backpressure. Some backpressure is part of the design, but the idea that an engine needs a lot of it is a myth; flow and pulse tuning matter more. Mechanics measure it with a gauge at the oxygen sensor port.

Pressure sensors before and after a particulate filter measure the difference to detect blockage.

A blocked catalytic converter or filter causes power loss and overheating. Removing emission parts to cut backpressure is illegal in many countries.