ASE Practice Test (L1: Advanced Engine Performance Specialist) 2

Question 1

A scan tool displays a long-term fuel trim (LTFT) of +18% at idle. What does this value indicate and what is the MOST likely cause?

Accepted Answer

The engine is running lean; the PCM has added 18% more fuel to compensate for a lean condition

Answer

The engine is running rich; the PCM is reducing fuel delivery by 18%

Answer

LTFT of +18% is normal operating range for most vehicles

Answer

The O2 sensor has failed lean and is providing false data to the PCM

Question 2

A misfiring condition is present on cylinders 1, 3, and 5 only (all odd-numbered cylinders). These cylinders share a common intake manifold runner. What is the MOST likely cause?

Accepted Answer

A vacuum leak or restricted intake affecting only the odd-cylinder bank's intake runners

Answer

Worn spark plugs on the odd cylinders only

Answer

Faulty ignition coil on one side of a wasted-spark system affecting only odd cylinders

Answer

Injector balance problems affecting only odd-numbered cylinders

Question 3

During an exhaust gas analysis, a technician finds elevated hydrocarbon (HC) readings with normal CO and CO2. What does this pattern most likely indicate?

Accepted Answer

Engine misfire or a cylinder not contributing to combustion

Answer

Rich air/fuel mixture causing incomplete combustion

Answer

Lean air/fuel mixture due to a vacuum leak

Answer

Catalytic converter efficiency degradation

Question 4

A vehicle fails an I/M (inspection/maintenance) emissions test with excessive NOx emissions. The EGR system is suspected. How does EGR help reduce NOx emissions?

Accepted Answer

EGR introduces inert exhaust gas to dilute the air/fuel mixture, lowering combustion temperatures that produce NOx

Answer

EGR adds oxygen to the combustion chamber to promote complete combustion of fuel

Answer

EGR recirculates unburned hydrocarbons to the intake to burn them completely

Answer

EGR increases intake manifold pressure to lean out the mixture and reduce NOx

Question 5

A Mass Air Flow (MAF) sensor reads 5.8 grams per second at idle. The specification for idle is 3.0-5.0 g/s. What are the likely drivability symptoms associated with a high MAF reading?

Accepted Answer

Rich running condition — the PCM delivers too much fuel based on the overstated airflow reading

Answer

Hard starting due to insufficient calculated fuel delivery

Answer

Lean running condition — the high reading causes the PCM to increase idle speed to compensate

Answer

No symptoms — the PCM will correct any MAF error with fuel trims

Question 6

A catalytic converter efficiency test using a scan tool shows the downstream O2 sensor switching almost as fast as the upstream O2 sensor. What does this indicate?

Accepted Answer

The catalytic converter has failed and is no longer effectively storing and releasing oxygen

Answer

The catalytic converter is functioning normally with high conversion efficiency

Answer

The downstream sensor is defective and must be replaced before a valid test can be performed

Answer

This pattern is normal on vehicles with secondary air injection systems

A scan tool displays a long-term fuel trim (LTFT) of +18% at idle.What does this value indicate and what is the MOST likely cause?

A scan tool displays a long-term fuel trim (LTFT) of +18% at idle.
What does this value indicate and what is the MOST likely cause?