Exam 31: Fuel Injection Diagnosis and Service

What is the difference between short-term and long-term fuel trim?

What problem may result from dirt buildup on an engine's throttle plates?

Which of the following sensors is used to modify the engine's air/fuel mixture based on oxygen in the exhaust?

Creating a large vacuum leak will cause the short-term fuel trim (STFT)and long-term fuel trim (LTFT)to decrease.

A fuel ____________________ is a solenoid-actuated fuel valve.

In sequential fuel injection systems, each injector has its own electrical ____________________ circuit and wiring.

Which of the following would NOT cause the fuel trim to be out of range?

When the system is running in open loop mode, the STFT value should be ____________________.

Fuel trim is being discussed. Technician A says a + 12.0 percent LTFT value indicates that the system is running 12 percent richer than normal. Technician B says LTFT should constantly change between positive and negative values when the system is running in closed loop. Who is correct?

An oxygen sensor must heat up to approximately _____ before functioning in its closed loop mode.

Never turn on the ignition switch when any fuel system component is disconnected.

An APP (accelerator pedal position)sensor is found on vehicles with ______.

A pulse ____________________ injector uses high current to open the injector.

A/F ratio sensors are being discussed. Technician A says the output voltage of these sensors is much higher than a conventional O₂S (oxygen sensor). Technician B say when the output of an A/F ratio sensor is looked at with an OBD-II generic scan tool, the voltage range will appear the same as a conventional O2S sensor, 0 to 1 volt. Who is correct?

Other than inspecting the electrical connections, there are usually no physical checks to mass airflow or manifold absolute pressure sensors.

Which of the following should be checked before proceeding with specific fuel injection and electronic control testing?

Technician A says a defective injector may cause cylinder misfiring at idle speed. Technician B says restricted injector tips may result in acceleration stumbles. Who is correct?

An exhaust gas analyzer can be used to determine whether an injector is leaking.

The engine must be at normal operating temperature before the O₂ sensor is tested.

Short-term and long-term fuel trim readings are being discussed. Technician A says a scale of 0 to 255 is used. Technician B says percentage is used. Who is correct?