Fuel Metering System Components. Isuzu S/T Isuzu

For 1990-2009 cars only

Makes 🢒 Isuzu 🢒 1997 🢒 S/T Isuzu - 2WD 🢒 Engine 🢒 Engine Controls - 2.2L 🢒 Fuel Metering System Components

Fuel System Operation

The SFI system consists of the following parts:

•	The fuel supply system (fuel tank, pump, pipes)

•	The fuel pump electrical circuit

•	Intake manifold assembly, including the following items:

-	The lower manifold assembly, including the following items:

•	The SFI fuel injectors

•	The fuel pressure regulator assembly

-	The upper manifold assembly, including the following items:

•	The throttle valve

•	The Idle Air Control (IAC) valve

•	The Throttle Position (TP) sensor

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 will cause no start.

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 (WOT).

Intake Manifold Assembly (Upper and Lower Manifold Assemblies)

The intake manifold is made up of the upper (1) and lower (5) manifold assemblies.

The upper manifold assembly is a single casting which includes the following items:

•	The upper portion of the air chamber (plenum)

•	The air inlet (fitted with a throttle valve)

This assembly replaces the individual throttle body assembly and plenum components.

The throttle valve controls the air flow into the engine, thereby, controlling engine output. The driver opens the throttle valve through the accelerator controls. During engine idle, the throttle valve is almost closed. The air flow control is handled by the Idle Air Control (IAC) valve (2). Various components generate the vacuum signals needed.

The nonadjustable, throttle shaft-driven, Throttle Position (TP) sensor (3) is attached to the upper manifold assembly opposite the throttle cam lever.

The lower manifold is a single casting that includes the intake runners and a longitudinal fuel passage with intersecting injector bores in each runner. This assembly replaces the individual fuel rail and the manifold components used in other systems. The information on the fuel injectors (4) and the pressure regulator (6) are covered separately.

Bottom Feed Type, Sequential Fuel Injectors


(1)	Housing and Solenoid Assembly
(2)	Pole Piece
(3)	Solenoid
(4)	Fuel Inlet Filter
(5)	Core Assembly
(6)	Core Seat
(7)	Spray Tip
(8)	Director
(9)	Spray Tip Housing
(10)	Core Spring
(11)	Screw and Guide Assembly
(12)	Solenoid Body

The bottom feed SFI assembly is a solenoid-operated device which the PCM controls. The SFI assembly meters pressurized fuel to a single engine cylinder. The PCM energizes the injector solenoid, which opens a ball valve. This allows the fuel to flow past the ball valve and through a recessed flow director plate.

This plate has machined holes that control the fuel flow. The plate generates a conical spray pattern of finely atomized fuel at the injector tip. The fuel is directed at the intake valve. The fuel becomes further atomized and vaporized before entering the combustion chamber.

The fuel injectors that remain partly open could cause a loss of pressure after the engine shuts down. This can cause long cranking times. The open fuel injectors could deliver fuel to the engine after the ignition is turned OFF causing dieseling.

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 engine OFF (zero vacuum), fuel pressure should be 284-325 kPa (41-47 psi). Whenever the pressure is too low, poor performance and a DTC P0171 could result. Whenever the pressure is too high, excessive odor and a DTC P0172 could result.

Throttle Position (TP) Sensor

The nonadjustable, throttle shaft-driven TP sensor is mounted on the upper manifold 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 to properly control the injector control signals (pulses).

Idle Air Control (IAC) Valve Assembly

Engine idle speed is controlled by the powertrain control module (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 (a step, or count), for each pulse. The commanded location, steps away from the seated position, 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 coolant temperature, park/neutral switch status, vehicle speed, battery voltage, and A/C refrigerant pressure, if equipped.

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The PCM learns the proper IAC valve positions 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 (information is retained after 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.

•	Engine idle speed is a function of total airflow into the engine based on IAC valve pintle position plus throttle valve opening plus calibrated vacuum loss through accessories.

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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 (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.

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The PCM normally resets the IAC valve pintle position once during each ignition cycle when vehicle speed increases above 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 this service procedure:

1.	Turn ON ignition, with the engine OFF.

2.	Turn OFF ignition for ten seconds.

3.	Start engine and check for proper idle operation.

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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, do not disconnect or connect the valve until 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.