Automotive Service Excellence (ASE) A8 Engine PerformanceEmissions Control Systems Diagnosis and RepairMedium
A vehicle arrives with a strong smell of raw fuel from the exhaust, particularly after cold starts. The 'Check Engine' light is illuminated with multiple misfire codes (P0300, P0301, P0302). Additionally, the exhaust oxygen sensor voltage on Bank 1 is consistently reading high (around 0.9V). What is the MOST likely cause?
- AA restricted exhaust system.
- BA large vacuum leak in the intake manifold.
- CA leaking fuel injector on Bank 1.
- DA faulty catalytic converter.
Show answer & explanationAnswer & explanation
Correct answer: C. A leaking fuel injector on Bank 1.
A high oxygen sensor voltage (0.9V) indicates a rich condition. Combined with raw fuel smell and misfire codes, this strongly points to excessive fuel delivery, such as a leaking fuel injector, leading to misfires and unburnt fuel.
Why the other options are wrong
- A. A restricted exhaust would cause a loss of power and potentially backpressure-related issues, but not directly cause a rich condition with high O2 sensor voltage and raw fuel smell.
- B. A vacuum leak causes a lean condition, leading to low O2 sensor voltage (around 0.1V) and potentially misfires, not a rich condition.
- D. A faulty catalytic converter would lead to increased HC/CO emissions, but it wouldn't be the primary cause of a rich condition or misfires indicated by the O2 sensor voltage and raw fuel smell.
Leaking Fuel Injector
A leaking fuel injector continuously drips fuel into the intake, creating an excessively rich condition, leading to misfires, raw fuel smell, and high O2 sensor voltage.
- Causes rich mixture (high O2 sensor voltage).
- Leads to misfires and unburnt fuel (raw smell).
- Can damage catalytic converter over time.
Memory trick: Raw fuel and high O2 volts? Injector's leaking, making the engine choke and misfire!