Exhaust Backpressure
The resistance or restriction in the exhaust system that slows down the flow of exhaust gases leaving the engine.
Exhaust backpressure is the resistance to flow encountered by exhaust gases as they travel from the engine's combustion chambers through the exhaust manifold, catalytic converter, muffler, and tailpipe. While some backpressure is normal due to pipe diameter and emissions devices, excessive backpressure restricts the engine's ability to breathe, hurting performance.
Excessive backpressure is typically caused by a restriction in the exhaust system, such as a clogged or melted catalytic converter, a crushed exhaust pipe, or a collapsed internal baffle inside the muffler. Symptoms of high backpressure include a severe loss of engine power (especially at high speeds), poor fuel economy, engine overheating, and a lack of throttle response.
Technicians diagnose exhaust backpressure issues by removing the pre-catalytic oxygen sensor and installing a pressure gauge in its port. With the engine idling, backpressure should be less than 1.5 PSI; under acceleration, it should remain below 3.0 PSI. If backpressure is high, the restricted exhaust component must be identified and replaced to restore normal engine operation.