ASE4 Fuel, Air Induction, and Exhaust Systems 2

Question 1

A MAF sensor reads 2 g/s at idle but the normal range is 3–7 g/s. The engine runs lean. This indicates the MAF sensor is:

Accepted Answer

Reading too low, causing the ECM to underdeliver fuel

Answer

Reading too high, causing fuel delivery to be cut

Answer

Functioning normally

Answer

Causing a rich condition

Question 2

A throttle body has carbon deposits causing the idle to hunt. The BEST repair is to:

Accepted Answer

Clean the throttle body with approved cleaner and relearn the idle

Answer

Replace the throttle body assembly

Answer

Adjust the throttle stop screw to compensate

Answer

Replace the IAC motor

Question 3

During a fuel injector leak-down test, one injector causes a fuel pressure drop of 20 psi in 5 minutes while others show only 2–3 psi drop. This means that injector is:

Accepted Answer

Leaking internally and allowing fuel to drip into the intake

Answer

Clogged and not flowing enough fuel

Answer

Functioning within normal parameters

Answer

Sticking open during operation

Question 4

An engine has a rich exhaust odor and poor fuel economy. Long-term fuel trim (LTFT) reads -20%. This indicates:

Accepted Answer

The ECM has subtracted 20% fuel, indicating an excessive fuel delivery issue

Answer

The ECM is adding 20% more fuel to compensate for a lean condition

Answer

The O2 sensors are switching too slowly

Answer

The engine has a vacuum leak

Question 5

What is the primary purpose of the PCV (Positive Crankcase Ventilation) system?

Accepted Answer

To vent crankcase pressure and recycle blow-by gases into the intake

Answer

To recirculate exhaust gases to reduce NOx emissions

Answer

To supply fresh air to the fuel tank for vapor control

Answer

To pressurize the oil system for better lubrication

Question 6

A clogged PCV valve can cause which of the following symptoms?

Accepted Answer

Oil leaks due to excessive crankcase pressure

Answer

A lean condition and increased power

Answer

A rich condition from excess vacuum

Answer

Rough idle from too much intake air