Fuel Injection System - Isuzu I-Tec Isuzu Impulse I

DESCRIPTION

The I-TEC control system constantly monitors and controls engine operation. This lowers emissions while maintaining fuel economy and driveability. The Electronic Control Unit (ECU) controls the fuel injection system, ignition system, and turbocharger control system (if used).

The ECU governs fuel injection operation by reading data from the following sensors: oxygen sensor, crank angle sensor, vehicle speed sensor, coolant temperature sensor, airflow sensor, and throttle valve switch. The fuel delivery system consists of fuel tank, electric fuel pump, pressure regulator, and 4 fuel injectors.

Note. Fuel system operation will be covered in this article. Refer to I-TEC CONTROL SYSTEM article in COMPUTER CONTROLS section for additional information.

ELECTRONIC CONTROL UNIT (ECU)

See I-TEC CONTROL SYSTEM article in COMPUTER CONTROLS section.

AIR REGULATOR

Air regulator operates as an air by-pass during cold, fast idle conditions. When engine is cold, air regulator allows additional flow of air to enter intake manifold.

Temperature sensitive electric element closes regulator as engine temperature increases. Air regulator is independent of I-TEC system and is operated by the ignition switch through fuel pump relay.

VACUUM SWITCHING VALVE (VSV)

Controlled by ECU, the VSV regulates fuel pressure. Fuel pressure varies slightly according to intake manifold vacuum.

DATA SENSORS

See I-TEC CONTROL SYSTEM article in COMPUTER CONTROLS section.

Dropping Resistors

Dropping resistors reduce current flow to fuel injectors. They are in-line with fuel injector wiring.

Fuel Injectors

Fuel is metered into cylinders by electrically controlled solenoid valves in injectors. Injectors are energized through ECU.

Fuel Pressure Regulator

Pressure regulator governs flow of fuel to injectors. Pressure varies depending on different vehicle speed and load conditions.

Fuel Pump

Fuel pump is located in rear of vehicle. Pump is integral in design and must be replaced as assembly.

FUEL CUT SYSTEM

Controlled by the throttle position switch, this system shuts off fuel flow during vehicle deceleration to reduce exhaust emissions. With engine warm, vehicle at cruising speed, and throttle position switch returned to idle position, ECU reduces impulses to fuel injectors. A throttle position sensor is used with turbocharged engines. The sensor controls the fuel cut system.

IDLE SPEED

See TUNE-UP article in the TUNE-UP section.

THROTTLE VALVE SWITCH

1. Check that throttle valve is completely closed. Loosen throttle valve switch mounting screws slightly. Unplug connector harness at throttle valve.
2. While checking continuity between center (P) terminal and top (I) terminal, turn switch in clockwise direction until continuity is obtained.
3. When tester shows continuity, turn switch 1° in clockwise direction and lock in place. One degree of travel is equivalent to about 0.024" (0.6 mm) stroke of throttle valve stopper bolt.

Handling Precautions

1. I-TEC EFI system components and connectors are very sensitive to shock, distortion and water. Turn ignition switch to "OFF" position before unplugging any electrical connectors.
2. All I-TEC cables must be placed at least 4" (100 mm) away from high tension cables. Do not operate fuel pump without fuel. The fuel is used to lubricate pump.

Fuel System

1. Ensure all fuel hoses are tight and in good order. Check fuel lines and hoses for corrosion, cracks, or other signs of damage. Ensure that hoses are not collapsed, and that fuel filter is not clogged.
2. Make sure that there is no water in fuel tank or in any other part of system. Ensure that "UNLEADED" gasoline is being used.

See I-TEC CONTROL SYSTEM article in COMPUTER CONTROLS section.

Fuel Pressure Regulator & Vacuum Switching Valve

1. Install Fuel Pressure Gauge (J-33945) between pressure regulator and fuel distributor pipe. Unplug VSV at connector. Start engine and measure fuel pressure under ALL of the following conditions
2. Disconnect pressure regulator vacuum. Plug intake manifold side of hose. Fuel pump pressure should be about 35.6 psi (2.5 kg/cm 2 ) for normally aspirated engine; about 42.6 psi (3.0 kg/cm 2 ) for turbocharged engine.
3. Reconnect pressure regulator vacuum hose and allow engine to idle. Fuel pump pressure should be about 28.4 psi (2.0 kg/cm 2 ) for normally aspirated engine; about 35.6 psi (2.5 kg/cm 2 ) for turbocharged engine.
4. Shut off engine. Disconnect vacuum hose from pressure regulator. Fuel pump pressure should be 28.4 psi (2.0 kg/cm 2 ) or less for normally aspirated engine; 35.6 psi (2.5 kg/cm 2 ) for turbocharged engine.
5. Apply battery voltage directly to VSV. Reconnect pressure regulator vacuum hose and allow engine to idle at 900 RPM. Fuel pump pressure should be about 35.6 psi (2.5 kg/cm 2 ) for normally aspirated engine; about 42.6 psi (3.0 kg/cm 2 ) for turbocharged engine. If pressure remains unchanged, replace VSV valve.

Low Fuel Pressure

1. Apply battery voltage directly to fuel pump connector with jumper wires. Positive lead goes to Red wire and negative lead goes to Black wire. If pressure is normal, check pump circuit and relay.
2. If fuel pressure remains unchanged, check for restrictions on intake side of fuel pump. Restrictions in intake hose may cause abnormal vibrations in hose. Remove restrictions as necessary.
3. If no restrictions are found, replace defective pressure regulator. If fuel pressure still remains unchanged replace fuel pump.

Loss of Pressure Immediately After Pump Stops

Replace defective fuel pump and/or pressure regulator. Check fuel injectors for internal leaks and replace as necessary.

High Fuel Pressure

Check for restrictions in fuel return lines. Clean or replace as necessary. Replace defective fuel pump and/or pressure regulator.

1. Unplug fuel injector harness at injector and measure resistance across terminals. All injectors must have 2-3 ohms of resistance. If not, replace injector.
2. With engine running, check fuel injector operating noise with stethoscope. Normal operation of injectors is indicated when a regular "click" is heard which varies with engine speed. If not, replace injector.
3. Remove common chamber assembly. Remove all injectors with fuel hoses connected. Check for fuel leakage by operating fuel pump with battery voltage applied directly to fuel pump relay terminal (Black/Red wire). Leakage must be less than 2 drops per minute. If leakage exceeds limit, replace injector(s).

DROPPING RESISTOR

1. Disconnect dropping resistor wiring at connector. Measure resistance between center terminal of dropping resistor connector and other terminals. (Scheme 25)
2. Standard resistance at all terminals should be 5-7 ohms. If any of measurements deviates from standard value, dropping resistor assembly must be replaced.

Checking Dropping Resistor. Scheme 25

Fast Idle Check

The engine idling speed must be slightly higher than normal immediately after starting (cold) engine. The engine idle speed should normalize as the engine temperature increases.

Leakage Test

1. Warm engine to operating temperature. Disconnect hose between air regulator and throttle valve body at throttle valve body. Plug hole in throttle valve body.
2. Start engine. Check for variation in engine speed by closing and opening end of air regulator hose. Engine speed should vary less than 50 RPM. If variation is more than specified, replace air regulator.

Resistance Check (No Fast Idle)

1. Disconnect air regulator harness at connector. Measure resistance across air regulator terminals. Standard resistance is 38-42 ohms. Replace air regulator assembly if resistance exceeds specified range.
2. Turn ignition switch to "ON" position and check voltage at air regulator connector. If voltage is present, replace defective air regulator. If voltage is not present, check wiring leading to air regulator and repair as necessary. If wiring is okay, replace defective fuel pump relay.

Preliminary Inspection

Check operation of accelerator and control cables for smoothness. Valve stopper must make firm contact with throttle valve stopper screw when throttle valve is released.

Note. Throttle valve stopper screw is factory set and sealed with paint. Setting should not be disturbed unless absolutely necessary.

Throttle Valve Switch Resistance Test

Unplug throttle valve switch harness at connector. Make continuity test across terminals with accelerator pedal depressed as indicated in table.

Testing Throttle Valve Switch Check continuity between terminals. Scheme 26

THROTTLE VALVE SWITCH RESISTANCE TEST - (Ohms)

Throttle Position Sensor Test (Turbo Only)

Turn ignition on. Disconnect throttle position sensor harness at connector. Place circuit tester positive lead in "A" terminal. (Scheme 27) Measure voltage between terminal and ground.

THROTTLE POSITION SENSOR TEST

Testing Throttle Position Sensor. Scheme 27

Normally Aspirated Engine

1. Warm engine to operating temperature. Turn ignition switch to "OFF" position. Unplug throttle valve switch harness at connector. Insert fine wire into upper (idle) terminal, then make connections at connector with wire pulled part way out. (Scheme 28)
2. Start engine and run at 2500-3000 RPM. Ensure engine speed lowers to about 1250 when battery voltage is applied to wire extending from idle terminal. Engine shake may occur at about 1250 RPM. It is normal during test procedure.

FUEL CUT SYSTEM TEST - NON-TURBO MODELS

Fuel Cut System Test (Non-Turbo Models). Scheme 28

Scheme 29

1. Warm engine to operating temperature. Turn ignition switch to "OFF" position. Unplug throttle valve switch harness at connector. Insert fine wire into upper (idle) terminal, then make connections at connector with wire pulled part way out. (Scheme 28) (Scheme 29): Fuel Cut System Test (Turbo Models)
2. Disconnect throttle position sensor at connector. Use a jumper wire to connect throttle valve switch and the same side of harness. (Scheme 29) Start engine and run at 2500-3000 RPM.
3. Ensure engine speed lowers to about 1250 when battery voltage is applied to wire extending from idle terminal. Engine shake may occur at about 1250 RPM, it is normal during test procedure.

Note. Fuel cut is controlled by the throttle position sensor. Fuel injection is controlled by the throttle switch.

FUEL CUT SYSTEM TEST - TURBO MODELS

Removal & Installation

Remove bolts securing airflow sensor. Loosen clamp bolt and remove sensor from air cleaner. Check by-pass circuit for contamination and clean with carburetor cleaner. To install, reverse removal procedure.

Checking Airflow Sensor By-Pass Circuit. Scheme 30

Remove insulator flange nut. Remove fuel filter bolt. Disconnect rubber hoses. Remove filter insulator. Remove fuel filter. To install, reverse removal procedure.

Remove rear seat assembly. Unplug electrical harness at terminal located under right side part of rear seat. Disconnect and plug rubber hoses from fuel pump. Remove pump guard. Remove pump from bracket. To install, reverse removal procedure.

Disconnect boost pump-to-return line hose. Disconnect boost pump-to-vapor separator hose. Remove boost pump assembly and bracket. Remove boost pump-to-vapor separator hose. Remove vapor separator. To install, reverse removal procedure.

I-TEC System Wiring Diagram. Scheme 31