hw 7,8 Flashcards
A disconnected vacuum hose on a fuel pressure regulator may cause excessive fuel pressure.
True’.
SFI is a type of PFI fuel system.
True’.
Inertia switches open the fuel pump circuit in case of a severe impact.
True
Fuel system pressure should be relieved with the engine running.
False
The octane number indicates the antiknock quality of gasoline.
True’
Throttle body fuel injection systems provide improved fuel metering when compared to:
Carburetors
Technician A says fuel that has low volatility can cause a buildup of deposits in the combustion chamber. Technician B says liquid gasoline will not burn. Who is correct?
Both A and B
When the pressure in the intake manifold increases the fuel pressure regulator on a port fuel injection system:
Increases fuel pressure
The acceptable amount of alcohol mixed with gasoline is
Up to 15%
Technician A says to relieve pressure on an EFI system, a pressure gauge may be connected to the fuel pressure test port and the bleed valve on the gauge opened with the bleed hose installed in an approved container. Technician B says before fuel system components on an EFI system can be removed, the fuel system pressure must be relieved. Who is correct?
Both A and B
Technician A says the fuel rail delivers fuel to the fuel injectors. Technician B says the throttle body in a port fuel injection system controls the amount of fuel entering the engine. Who is correct?
Technician A only
The fuel pressure regulator in a typical mechanical returnless fuel system is located:
At the fuel pump sender assembly
Technician A says a rich air-fuel mixture may be the result of higher-than-normal fuel pressure. Technician B says higher-than-normal fuel pressure causes a lean air-fuel ratio. Who is correct?
Technician A only
High fuel pressure may be caused by a:
Defective fuel pressure regulator/Fuel return line that is restricted
Technician A says low fuel pressure may be caused by a restricted fuel filter. Technician B says when testing fuel pressure, make sure the specifications are either for the engine running or the engine off. Who is correct?
Both A and B
Discussing a multi-port injected system: Technician A says the powertrain control module provides the proper air-fuel ratio by controlling injector pulse width. Technician B says the powertrain control module controls the fuel pressure to provide the proper air-fuel ratio. Who is correct?
Technician A only
Technician A says that if the engine stalls and the ignition switch is on, the one-way check valve prevents fuel flow from the pump to the fuel filter and fuel system. Technician B says that when the engine is shut off, the one-way check valve prevents fuel flow from the under-hood fuel system components into the fuel pump and tank. Who is correct?
Technician B only
Technician A says reducing spark advance can cause spark knock. Technician B says excessive carbon deposits can cause spark knock. Who is correct?
Technician B only
All of the following are added to gasoline today except?
Tetraethyl lead
Direct gasoline injection systems can spray fuel directly into the combustion chamber when the intake valve is opened.
True
The idle air control (IAC) valve controls the amount of fuel entering the engine to maintain proper idle speeds.
False
Central multiport fuel injection systems use one injector and separate fuel tubes that run to each cylinder.
True
MAP sensors read any pressure above a perfect vacuum.
True
The intake manifold turning valve (IMTV) makes the intake manifold an active manifold, that is, it responds to changing demands.
True
Long term fuel trim will change in an attempt to keep short term fuel trim near 0.
True
An air-fuel ratio sensor does a better job than an O2 sensor of determining just how rich or lean an engine is running.
True
Clogged fuel injectors will cause long term fuel trim to take away fuel.
False
Technician A says if the IAC value is at or near zero on a speed density system there may be a manifold vacuum leak. Technician B says if the IAC value is too high there may be a build-up of carbon on the backside of the throttle plate. Who is correct?
Both A and B
To help isolate a clogged or dirty injector
Perform an injector balance test
Technician A says acceleration stumbles may be the result of restricted injector tips. Technician B says cylinder misfiring at idle speed may be caused by a defective injector. Who is correct?
Both A and B
Injector pulse width is
The amount of time the injector is turned on
Technician A says the poppet nozzles in the CMFI system are opened by fuel pressure. Technician B says the computer opens the poppet nozzles in the CMFI system. Who is correct?
Technician A only
Technician A says a speed density EFI system is one in which the computer calculates the amount of air entering the engine. Technician B says that to determine the air entering the engine in a speed-density system, the computer uses the TPS and ECT signals. Who is correct?
Technician A only
The purpose of the manifold vacuum connection to the fuel pressure regulator is to
Maintain the same pressure drop across the injectors at idle speed and wide-open throttle
Technician A says higher fuel pressure at wide-open throttle is the result of low manifold vacuum to the pressure regulator in the SFI system. Technician B says higher fuel pressure at wide-open throttle is maintained by the PCM in the SFI system to enrich the air/fuel ratio for better acceleration. Who is correct?
Technician A only
Technician A says coolant is routed through the throttle body to warm the incoming air. Technician B says the throttle body is warmed by coolant to prevent it from freezing. Who is correct?
Technician B only
Multiport fuel injection systems do not require a
Camshaft position sensor
Technician A says a SFI requires both crank and cam position sensors. Technician B says SFI engines can also function as MFI if necessary. Who is correct?
Both A and B
Technician A says an injector ohm test is the most accurate method of testing a fuel injector’s operation. Technician B says an injector ohm test can only confirm a defective injector winding. Who is correct?
Technician B only
