Chapter 30 Test

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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


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