Chapter 30 Test
In most TBI systems, the fuel pressure is maintained at _____.
10 to 25 psi
Typical fuel injector pulse widths range from _____ to _____ milliseconds.
1; 10
Technician A says the fuel pressure regulator in a PFI system senses manifold vacuum and continually adjusts the fuel pressure to maintain a constant pressure drop across the injector. Technician B says the pressure regulator in a PFI system is designed to provide a constant pressure to the fuel injector throughout the range of engine loads and speeds. Who is correct?
A only
Technician A says the oxygen sensor (O2S) detects misfires by monitoring the amount of unburned fuel in the exhaust system. Technician B says a heating element inside the sensor allows the sensor to reach operating temperature quickly and to maintain its temperature during periods of idling or low engine load. Who is correct?
B only
While discussing central port injection (CPI), Technician A says the poppet nozzles are opened by the computer. Technician B says the poppet nozzles are opened by fuel pressure. Who is correct?
B only
Technician A says in order to meet OBD standards, diesel control systems use many of the same inputs as a gasoline engine (such as the MAP, IAT, MAF, TP, CKP, and CMP sensors). Technician B says the pressure in the fuel rail of a modern common rail diesel engine can range from 2,000 psi (138 bar) to 25,000 psi (1,724 bar). Who is correct?
Both
Technician A says throttle-by-wire systems [ETC] eliminate the need for a cruise control actuator. Technician B says ETC also allows the PCM to be more effective when limiting engine and vehicle speeds. Who is correct?
Both
The longest injector pulse width occurs during ______.
Cold starting
Because modern engines heat up rapidly, heated oxygen sensors (HO2S) are not needed.
False
MAP output is the same as what is measured on a vacuum gauge. When intake vacuum is high, MAP voltage is high.
False
OBD-II systems have only one O2S [oxygen sensor] in the exhaust system, located after the catalytic converter (downstream).
False
Technician A says the computer uses the TP sensor and ECT sensor signals to determine the amount of air entering the engine in a speed-density system. Technician B says the computer uses the TP sensor and oxygen sensor signals to determine the amount of air entering the engine in a speed-density system. Who is correct?
Neither
In closed loop, the PCM adjusts the pulse width according to inputs from a variety of sensors, but primarily the _____.
O2S
Only _____ meets the requirements of OBD II regulations.
SFI [sequential fuel injection]
IAC [idle air control] valves are operated by a ______.
Stepper motor
An O-ring at the base of a fuel injector ______.
all answers correct
Fuel injectors are ______.
both "top fuel-feeding devices" and "bottom fuel-feeding devices"
The throttle body of a port fuel injected engine may include any of the following components EXCEPT:
oxygen sensor
Fuel trim is being discussed. Technician A says a positive fuel-trim value means the PCM detects a lean mixture and is increasing the pulse width to add more fuel to the mixture. Technician B says LTFT [long-term fuel trim] is erased when the ignition is turned off. Who is correct?
A only
Technician A says an air/fuel ratio sensor responds to minor changes in the air/fuel mixture. Technician B says that when an air/fuel ratio sensor is used on an OBD-II vehicle, both the upstream and downstream sensors must be air/fuel ratio type sensors. Who is correct?
A only
The auxiliary air valve is controlled by the PCM.
False
The mass airflow (MAF) sensor measures changes in the intake manifold pressure that result from changes in engine load and speed.
False
Bottom-feed injectors used in throttle body injection [TBI] systems are able to use fuel pressures as low as 10 psi.
True
CPI [central multiport injection] injectors are located in the lower half of the intake manifold.
True
Fuel trim can be monitored for diagnostic purposes.
True
Idle speed control is a function of the PCM.
True
PFI systems use at least one injector at each cylinder.
True
The strength of the mass airflow (MAF) signal is determined by the energy needed to keep the heated sensing element at a constant temperature above the incoming ambient air temperature.
True
To prevent fuel boiling in the TBI assembly, the fuel pressure is kept high.
True
Each fuel injector has a _____-wire connector.
Two
