The fuel metering system is made up of the following parts:
| • | The fuel supply components (the fuel tank, the fuel pump, and
the fuel lines). |
| • | The fuel rail assembly, including: |
| - | The fuel pressure regulator |
| • | The throttle body assembly, including: |
| - | The idle air control (IAC) valve |
| - | The throttle position (TP) sensor |
Fuel Pump Electrical Circuit
When the ignition switch is turned to the ON position, the PCM energizes
the fuel pump relay for 2 seconds allowing the fuel pump to pressurize
the fuel system. If the PCM does not receive any ignition reference pulses
(engine cranking or running) within 2 seconds, the PCM de-energizes
the fuel pump relay, this causes the fuel pump to stop.
An inoperative fuel pump relay can result in long cranking times.
Accelerator Controls
The accelerator control system is a cable type and there are no linkage
adjustments. Therefore, the only specific cable for each application must
be used. When work has been performed on the accelerator controls, always
make sure that all components are installed correctly and that the linkage
and cables are not rubbing or binding in any manner. The throttle should
operate freely without binding between full closed and wide open throttle.
Fuel Injectors
The fuel injector assembly
is a solenoid-operated device, controlled by the PCM, that meters pressurized
fuel to a single engine cylinder. The PCM energizes the
fuel injector solenoid (1) which opens a ball valve (2)
allowing fuel to flow past the ball valve, and through a director plate (3)
at the injector outlet. The director plate has machined
holes that control the fuel flow, generating a conical spray
pattern of finely atomized fuel at the injector tip. Fuel
from the tip is directed at the intake valve, causing
the fuel to become further atomized and vaporized before entering the
combustion chamber. A fuel injector that is stuck partly
open causes a loss of pressure after the engine is shut
down, so long crank times may be noticed on some engines. Dieseling can
also occur because some fuel could be delivered to the engine after the
ignition is turned OFF.
Fuel Injector Part Number Location
The eight digit part number (2)
is identified on the fuel injector body (1). A 4-digit build
date (3) is also located on the fuel injector body. the first digit (4)
indicates the month in which the fuel injector was built. For example, 1=January,
2=February, ..., 9=September, O=October, N=November and D=December. The
second and third digit (5) indicates the day of the month. The fourth
digit (6) indicates the last digit of the year in which the fuel
injector was built. Finally, the fifth digit (7) indicates which
plant shift built the fuel injector.
Fuel Pressure Regulator Assembly
The fuel pressure regulator
assembly is a diaphragm-operated relief valve with fuel pump pressure on one
side, and a regulator spring pressure and intake manifold vacuum on the
other side. The regulator's function is to maintain a constant pressure
differential across the injectors at all times. The pressure regulator
compensates for engine load by increasing the fuel pressure as the engine
vacuum drops. The fuel pressure regulator is serviced as a complete assembly.
With the ignition on and the engine off (zero vacuum), fuel pressure should
be 358-405 kPa (52-58 psi). Whenever the pressure is too
low, reduced performance and a DTC P0171 could result. Whenever the pressure
is too high, excessive odor and a DTC P0172 could result.
The last five digits of the part number (1) are identified on
the fuel pressure regulator. A five digit build date (2) is also located
on the fuel pressure regulator. The first three digits indicate the day
of the year in which the fuel pressure regulator was built. The fourth
digit indicates the year in which the fuel pressure regulator was built.
Finally, the fifth digit indicates which plant shift built the fuel pressure
regulator.
Throttle Position (TP) Sensor
The nonadjustable, throttle shaft-driven TP sensor is mounted on the
throttle body assembly opposite the throttle cam lever. The TP sensor
senses the throttle valve angle and relays the information to the powertrain
control module (PCM). Knowledge of throttle angle is needed by the PCM inorder
to properly control the injector control signals (pulses).
Idle Air Control (IAC) Valve Assembly
The engine idle speed is controlled by the PCM through the IAC valve (1)
mounted on the throttle body. The PCM sends voltage pulses to the IAC valve
motor windings causing the IAC valve pintle (3) to move in toward
the seat, or out away from the seat a given distance, called a step or a
count, for each pulse. The commanded location can be observed as a number
of counts displayed on a scan tool. The pintle movement controls the airflow
around the throttle valve (2), which in turn, controls engine idle
speed: Pintle Extended=Decrease RPM=Lower Counts, Pintle Retracted=Increase
RPM=Higher Counts.
| • | The controlled or desired idle speed for all engine operating
conditions is programmed into the EEPROM of the PCM. The programmed engine
speeds are based on the coolant temperature, the park/neutral switch status,
the vehicle speed, the battery voltage, and the A/C refrigerant pressure
(if equipped). |
| • | The PCM learns the proper IAC valve positions in order to achieve
warm, stabilized idle speeds (RPM), desired for the various conditions (P/N
or Drive, A/C on or off, if equipped). This information is stored in PCM
keep alive memories and retained after the ignition is off. All other IAC
valve positioning is calculated based on these memory values. As a result,
engine variations due to wear and variations in minimum throttle valve position,
within limits, do not affect engine idle speeds. This system provides correct
idle control under all conditions. This also means that disconnecting power
to the PCM can result in incorrect idle control or the necessity to partially
depress the accelerator when starting, until the PCM relearns idle control. |
| • | The engine idle speed is a function of the total airflow into
the engine based on the IAC valve pintle position, the throttle valve opening,
and a calibrated vacuum loss through accessories. |
| • | The minimum throttle valve position is set at the factory with
a stop screw. This setting allows enough air flow by the closed throttle valve
to cause the IAC valve pintle to be positioned a calibrated number of steps
or counts from the seat during controlled idle operation. The minimum throttle
valve position for this engine is not the same as the minimum idle speed
associated with other fuel injected engines. The throttle stop screw is
filled at the factory following an adjustment. |
| | Important: DO NOT try to remove the filler and readjust the stop screw. Misadjustment
may set a DTC P0506 or a DTC P0507.
|
| • | The PCM normally resets the IAC valve pintle position once during
each ignition cycle when vehicle speed increases above 32 km/h (20 mph)
on moderate acceleration. During the reset, the PCM commands the IAC valve
pintle to retract completely, then move in to the seated position (to establish
the zero count position), and then back out to the desired position. The
IAC is relearned only once per ignition cycle. |
| • | The IAC valve also can be reset without driving the vehicle by
using following procedure: |
| 1. | Turn on the ignition, leaving the engine off. |
| 2. | Turn off the ignition for 10 seconds. |
| 3. | Start the engine and verify the proper idle operation. |
| • | Whenever the IAC valve is disconnected and reconnected while the
engine is running, the resulting IAC valve counts may not correspond with
the actual IAC valve pintle position. When servicing the IAC valve, only
disconnect or connect the valve after the ignition has been off for at least
10 seconds. This allows time for the PCM to move the IAC valve to
the 150 count position where the valve is parked while the ignition is off.
Whenever this procedure is not followed, the PCM will lose track of IAC
valve position resulting in starting or idle control problems until the
IAC valve is reset and pintle position is relearned. |
| • | IAC system problems may cause improper idle speeds, resulting
in a DTC P0506 or a DTC P0507. The DTC P0506 or the DTC P0507 tables should
be used to diagnose these problems. |
