Automotive Service Excellence (ASE) A8 Engine PerformanceFuel, Air Induction, and Exhaust Systems Diagnosis and RepairMedium
A vehicle experiences a sudden loss of power under heavy acceleration, but runs normally at idle and light throttle. The engine does not produce any abnormal noises. Which of the following is the MOST likely cause?
- AA cracked intake manifold.
- BA clogged catalytic converter.
- CA faulty mass airflow (MAF) sensor.
- DA restricted exhaust muffler.
Show answer & explanationAnswer & explanation
Correct answer: B. A clogged catalytic converter.
A clogged catalytic converter restricts exhaust flow, which becomes most apparent under heavy acceleration when the engine is trying to move a large volume of exhaust gases. At idle or light throttle, the restriction may not be significant enough to cause noticeable performance issues.
Why the other options are wrong
- A. A cracked intake manifold would primarily cause a vacuum leak, leading to a lean condition and rough idle, not typically a sudden loss of power only under heavy acceleration.
- C. A faulty MAF sensor could cause various performance issues and driveability problems, but a sudden loss of power specifically under heavy acceleration with normal idle is more indicative of an exhaust restriction.
- D. A restricted muffler would also cause a loss of power under acceleration, similar to a clogged catalytic converter, but the catalytic converter is a more common and severe restriction point.
Catalytic Converter Restriction Symptoms
A clogged catalytic converter causes a loss of engine power, especially under heavy acceleration, due to restricted exhaust flow. Symptoms may be less noticeable at idle.
- Loss of power under load.
- Engine may feel 'choked' or 'bog down'.
- Can cause excessive heat under the vehicle.
- Backpressure test can confirm.
Memory trick: Heavy load, exhaust choked.