NAPA - National Automotive Parts Association Certified Mechanic Engine Performance Questions and Answers

Question 1

A vehicle with a P0171 (System Too Lean Bank 1) trouble code shows a Long Term Fuel Trim (LTFT) of +25% at idle.
When the engine is held at 2,500 RPM, the LTFT value drops to +5%.
What is the MOST likely cause of this condition?

Accepted Answer

A vacuum leak on the intake manifold after the MAF sensor.

Answer

A faulty fuel pump.

Answer

A clogged fuel injector on Bank 1.

Answer

A malfunctioning oxygen sensor on Bank 1.

Question 2

The driver of a vehicle reports a noticeable pinging or knocking sound from the engine during moderate acceleration, particularly when going up hills. No check engine light is on. Which of the following is the most probable cause?

Accepted Answer

A clogged or inoperative EGR valve.

Answer

A stuck-open EGR valve.

Answer

An overly rich fuel condition.

Answer

Excessively retarded ignition timing.

Question 3

Which of the following symptoms is MOST likely to be caused by a Variable Valve Timing (VVT) solenoid that is stuck in the fully advanced position?

Accepted Answer

An extremely rough idle or stalling when coming to a stop.

Answer

A lack of power at high engine RPM.

Answer

A no-start condition where the engine cranks but does not fire.

Answer

Black smoke from the exhaust during acceleration.

Question 4

A technician is diagnosing a P0304 code (Cylinder 4 Misfire) on an engine with a Coil-On-Plug (COP) ignition system. The technician swaps the ignition coil from cylinder 4 with the coil from cylinder 1. After clearing the codes and test-driving the vehicle, a new code, P0301, is stored. What is the next logical step?

Accepted Answer

Replace the ignition coil that was originally on cylinder 4.

Answer

Replace the fuel injector for cylinder 4.

Answer

Perform a cylinder compression test on cylinder 4.

Answer

Check the PCM driver circuit for cylinder 1.

Question 5

A vehicle is brought to the shop with a 'crank, no-start' condition. Using a scan tool, the technician confirms that the engine RPM is displaying a steady 200 RPM while cranking. This observation makes which of the following components the LEAST likely cause of the no-start condition?

Accepted Answer

The crankshaft position (CKP) sensor.

Answer

The fuel pump.

Answer

The ignition control module.

Answer

A blown fuse for the fuel injectors.

Question 6

A technician measures fuel pressure on a port-injected engine. With the key on, engine off (KOEO), the pressure is 58 psi (within spec). As soon as the engine is started, the pressure drops and remains at 25 psi, causing a lean condition and poor performance. What is the MOST likely cause?

Accepted Answer

A restricted fuel filter or a weak fuel pump.

Answer

A leaking fuel pressure regulator diaphragm.

Answer

One or more leaking fuel injectors.

Answer

An open in the power supply to the fuel pump.

A vehicle with a P0171 (System Too Lean Bank 1) trouble code shows a Long Term Fuel Trim (LTFT) of +25% at idle.When the engine is held at 2,500 RPM, the LTFT value drops to +5%.What is the MOST likely cause of this condition?

A vehicle with a P0171 (System Too Lean Bank 1) trouble code shows a Long Term Fuel Trim (LTFT) of +25% at idle.
When the engine is held at 2,500 RPM, the LTFT value drops to +5%.
What is the MOST likely cause of this condition?