The fuel pressure regulator
is a diaphragm-operated pressure relief valve consisting of a diaphragm (3),
a spring (2), and a valve (4). The fuel pressure regulator
keeps the fuel pressure applied to the fuel injector at
a pressure much more than the pressure in the intake manifold.
The pressure applied to chamber A (2) of the fuel pressure regulator
is the intake manifold pressure. The pressure applied to chamber B (5) of
the fuel pressure regulator is fuel pressure. When the
fuel pressure rises at least 210 kPa (30 psi)
higher than the intake manifold pressure, the fuel pushes
a valve in the regulator open and excess fuel (6) returns
to the fuel tank via the fuel return pipe.
The fuel feed, return pipes and hoses carry the fuel from the fuel tank
to the fuel injectors and back to the fuel tank. These pipes and hoses
are attached to the chassis of
the vehicle, and should be inspected periodically
for kinks or dents that may restrict
the fuel flow.
The fuel vapor pipe and hoses carry the fuel vapors from the fuel tank
to the evaporative emission canister. The
fuel vapors are stored in the canister
when the engine is not running. When
the engine is running at the normal operating temperature
and the accelerator pedal is
depressed, the powertrain control module (PCM) will command
the evaporative emission canister
purge valve to open and allow the stored fuel vapors to
be purged into the intake manifold where
they will be burned in the combustion
process.
The on-board refueling
vapor recovery (ORVR) system is an on-board vehicle system designed to recover
fuel vapors during the vehicle refueling operation. Instead
of allowing fuel vapors to escape to the atmosphere the
ORVR system transports the vapor to the EVAP canister for
use by the engine. The flow of liquid fuel down the fuel
filler neck provides a liquid seal that prevents fuel vapor
from leaving the fuel system. The ORVR system architecture
varies from platform to platform. Some of the items listed
below are optional depending on the platform application.
The following is a list of all the ORVR system components with
a brief description of their operation:
The accelerator control system is cable-operated. When the accelerator
pedal is depressed, the cable pulls the throttle lever open, increasing the
throttle plate opening. When the accelerator pedal is released,
the throttle lever spring pressure returns the throttle lever
to the idle position, decreasing the throttle plate opening.
The function of the fuel metering system is deliver the correct amount
of fuel to the engine under all operating conditions. Fuel is delivered
to each cylinder by the fuel injectors. The fuel injectors
are controlled sequentially by the powertrain control module
(PCM). The PCM bases the control of the fuel injectors on several
important engine parameters. These engine parameters include
the following:
The two most important inputs for fuel control are the mass air flow
(MAF) sensor and the fuel control heated oxygen sensors (HO2S). The MAF sensor
provides the powertrain control module (PCM) with engine air
intake quantity, while the fuel control HO2S provides the PCM
with exhaust stream oxygen content information. Determining air
density is critical to proper air/fuel management. Air density is
primarily derived from the MAF sensor input. The MAF sensor measures
the air volume and determines the air density. Larger volumes
of air and denser air masses require additional fuel. The information
from the MAF sensor is used by the PCM in order to modify the
fuel injector pulse width.
The PCM modifies the air/fuel mixture by changing the injector pulse
width signal sent to the injectors. By constantly measuring the air intake
and the exhaust oxygen content and adjusting the injector pulse
width, the air fuel ratio is kept very close to the optimal
14.7:1. This is the range at which the three-way catalytic converter
(TWC) operates most effectively and at which the emissions of
this vehicle are kept to a minimum. The constant tailoring of
the air/fuel ratio is based upon feedback from the HO2S and
is referred to as closed loop operation.
