Engine Performance (A8)Câu 95 / 120
Technician A says a vacuum leak causes a rich condition. Technician B says a vacuum leak adds unmetered air and causes a lean condition, especially at idle. Who is correct?
a.Technician A only
b.Technician B only
c.Both A and B
d.Neither A nor B
Giải thích
A vacuum leak lets extra air enter after the mass airflow sensor, leaning the mixture and often causing a rough idle and positive fuel trim. Technician B is correct. Smoke testing helps locate intake leaks.
Luyện miễn phí toàn bộ 120 câu hỏi — không cần đăng ký.
Câu hỏi liên quan cùng chủ đề
- An oxygen (O2) sensor in the exhaust provides feedback to the PCM about:
- A diagnostic trouble code (DTC) of P0301 indicates:
- Technician A says a positive long-term fuel trim of +20 percent means the PCM is adding fuel to correct a lean condition. Technician B says positive trim means the engine is running rich. Who is correct?
- Technician A says a rich air-fuel mixture can raise tailpipe CO and HC. Technician B says the oxygen sensor helps the PCM keep the mixture near stoichiometric. Who is correct?
- Technician A says the MAF sensor measures the mass of air entering the engine so the PCM can meter fuel. Technician B says a dirty MAF can cause hesitation and fuel-trim errors. Who is correct?
- A P0420 code (catalyst efficiency below threshold) most often indicates:
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