Sample Review Questions:
1.
Counterman A says a “speed-density” fuel injection system uses a mass
airflow sensor to monitor the volume of air entering the engine.
Counterman B says the signal from the mass airflow sensor is used to
control the air/fuel mixture. Who’s right?
a. Counterman A only
b. Counterman B only
c. Both Counterman A and B
d. Neither one
2. A fuel filter plugged with rust probably indicates what?
a. Dirty fuel injectors
b. Dirty fuel pressure regulator
c. Bad gas contaminated with water
d. Corrosion inside a steel fuel tank
3. Which of the following would NOT prevent an electric fuel pump from running?
a. Faulty fuel pressure regulator
b. Bad fuel pump fuse or relay
c. Wiring problem in fuel pump circuit
d. Open inertia safety switch
4.
Counterman A says dirty fuel injectors can cause poor fuel economy,
poor performance and engine misfires. Counterman B says a defective
idle speed control (ISC) motor can upset the idle fuel mixture. Who’s
right?
a. Counterman A only
b. Counterman B only
c. Both Counterman A and B
d. Neither one
ANSWER KEY: 1B, 2D, 3A, 4A
EXPLANATIONS:
1.
A mass airflow (MAF) sensor is used on many-fuel injected engines to
monitor the volume of air entering the engine. The MAF sensor is
located between the air filter and throttle, and generates a signal
when air flows past a heated wire. The amount of cooling the wire
undergoes is proportional to airflow. The PCM uses this information to
adjust the air/fuel mixture. But on speed-density systems, there is no
MAF sensor.
2. The fuel filter is usually located between the
fuel tank and injector fuel rail on the engine. In some applications,
the filter may be located inside the tank. If the filter is plugged
with rust, the rust came from corrosion inside the fuel tank. Replacing
the fuel filter may restore the flow of fuel, but the filter will
likely plug again unless the fuel tank is cleaned or replaced. Bad gas
contaminated with water can be a contributing factor to rust inside the
tank, but by itself won’t plug the filter.
3. Electric fuel
pumps are often replaced unnecessarily because of misdiagnosis. A dead
fuel pump obviously won’t produce any fuel pressure. But the problem
may not be the pump but the pump’s voltage supply. Possible causes
include a blown fuse, bad fuel pump relay, wiring problem, bad driver
circuit in the PCM, or anti-theft system issue. The fuel pressure
regulator is a mechanical device that maintains a certain level of fuel
pressure in the system. The regulator does not affect the operation of
the pump.
4. Fuel injectors can become clogged with fuel
varnish deposits if low-quality gasoline is used that does not contain
adequate levels of detergents and cleaners. Dirty injectors do not
deliver a normal quantity of fuel, causing the engine to run lean and
misfire.
Sections covered:
Automatic Transmission
Batteries
Brakes
Cooling System
Drivetrain
Emissions
Engine Mechanical Parts
Exhaust
Fuel System
HVAC
Gaskets
Ignition System
Manual Transmission
Suspension and Steering
Management