DESCRIPTION
Note. The Bosch AFC (L-Jetronic) Fuel Injection system is used on all models. However, variations may exist between model applications. This article covers the Bosch AFC system in general, with manufacturers' differences noted under SPECIAL FEATURES. For computer control information, see the appropriate article in the COMPUTER ENG CONTROLS section.
The Bosch Airflow Controlled (AFC) fuel injection system is an electronically controlled system operated by incoming airflow. The AFC fuel injection system also contains a feedback system which measures oxygen content of exhaust gases and maintains the air/fuel ratio at about 14.7:1.
The fuel injection system consists of an electric fuel pump, fuel pressure regulator, fuel damper, fuel injectors, Electronic Control Unit (ECU), and airflow meter. In addition, an air temperature sensor, throttle position sensor, coolant temperature sensor, oxygen sensor, catalytic converter, auxiliary air valve, idle speed control valve, throttle body, and electrical relays are used.
Note. Only primary sub-systems which affect fuel system operation will be covered in this article. For further information, see TUNE-UP article in the TUNE-UP section.
ELECTRIC FUEL PUMP(S)
Fuel under pressure from electric fuel pump flows through a fuel damper, fuel filter, injector fuel rail and fuel pressure regulator. Fuel pump(s) may be located on frame rail, in fuel tank or both. Electrical power for fuel pump operation during cranking mode is provided from starter relay via the fuel pump relay and ECU.
At idle, the airflow meter measuring flap opens slightly (about 5 degrees). This action closes the fuel pump contacts and provides power to fuel pump after engine has started.
With engine stopped, no airflow is present, measuring flap closes and fuel pump contacts are opened to cut power to fuel pump. This reduces the risk of fire, in case of a collision.
FUEL PRESSURE REGULATOR
The pressure regulator is a sealed unit which is divided by a diaphragm into 2 chambers (fuel and spring chambers). The fuel chamber receives fuel through the inlet side from the injector fuel rail. The spring chamber is connected to intake manifold vacuum.
At idle, intake manifold vacuum is high, the diaphragm is pulled down by intake manifold vacuum. Any excessive fuel is returned to the fuel tank. As the throttle is depressed, intake manifold vacuum decreases. The regulator increases fuel pressure to maintain the same fuel pressure-to-intake manifold vacuum difference as during high intake manifold vacuum.
FUEL INJECTORS
A fuel rail links the fuel pressure regulator with the fuel injectors. Each cylinder is provided with a solenoid-operated injector which sprays fuel toward the back of each intake valve. Vehicles are energized through the ignition switch. All models are grounded through the ECU. The injectors on some models are linked to resistors to reduce operating voltage to 3 volts and to protect injectors from power surges.
The ECU controls the injectors and the length of time they are open. The "open" time of the injector governs the amount of fuel delivered. The injectors deliver 1/2 the amount of fuel required once every crankshaft revolution.
ELECTRONIC CONTROL UNIT (ECU)
All components of the control system are electrically connected to the ECU. (Scheme 48) The ECU is a pre-programmed computer which receives and interprets data from various sensors to calculate the amount of fuel required by the engine to maintain efficiency with minimum exhaust emissions. The oxygen sensor informs the ECU of oxygen content of exhaust gases and the ECU constantly adjusts the air/fuel ratio by controlling the injector "open" time.
An automatic function of the ECU is to provide fuel enrichment whenever engine is cranked, regardless of engine temperature. This is activated by a direct electrical connection from the starter circuit to the ECU (most models). The ECU is a sealed unit, and no service is required.
Electronic Control Unit (ECU). Scheme 48
AIRFLOW METER
Airflow meter measures the amount of air aspirated and provides a signal to the control unit. The aspirated air applies force to the flap so that its opening angle is balanced with the return torque of the helical spring. The flap shaft is connected to a potentiometer, which corresponding with its opening angle, provides a voltage signal to the control unit.
After engine start-up, a set of contacts are closed to signal fuel pump operation. (Scheme 49)
Bosch AFC Airflow Meter. Scheme 49
AIR TEMPERATURE SENSOR
The air temperature sensor is an integral component of the airflow meter which converts temperature of incoming air into electrical signals. These signals are received by the ECU and processed to adjust the amount of fuel delivered by the injectors. The air temperature sensor is not serviceable.
THROTTLE BODY
The throttle body controls the intake airflow in response to accelerator pedal movement. Located between the airflow meter and the intake manifold, the throttle body shaft is connected to Throttle Position Sensor (TPS).
Most models have a dashpot mounted on the throttle body. The dashpot is used to decrease the intake air gradually when throttle valve is closed.
THROTTLE POSITION SENSOR (TPS)
A contact-type TPS is installed on the throttle chamber of all models. It converts throttle position into electrical signals to inform ECU of throttle position. Signals are sent to ECU when throttle is fully open or at idle. (Scheme 50) The open contacts prevent loss of power during sudden acceleration/deceleration by signaling ECU of the required fuel enrichment.
Contact-Type Throttle Position Sensor. Scheme 50
COOLANT TEMPERATURE SENSOR
This sensor provides ECU with engine temperature information relating to warm-up enrichment operation. Some models use a dual-sensor element which also signals the ignition computer (if equipped).
During warm-up period after a cold engine start, additional fuel is required to maintain engine performance. As engine temperature increases, the ECU decreases fuel enrichment until engine reaches normal operating temperature.
ELECTRICAL RELAYS
The various relays used with the electronic controls of the AFC injection system control power to injectors, fuel pump, ECU, and cold start system. The electrical relays may consist of one component for all relays or a combination of individual relays.
AUXILIARY AIR VALVE
Most models with Bosch AFC fuel injection use an Auxiliary Air Valve (AAV) to shorten engine warm-up time. The AAV supplies additional air into the intake system which increases engine RPM during a cold start.
The AAV consists of an electrically heated bi-metallic strip, movable disc, and air by-pass channel. The heater coil on the bi-metallic strip is energized by the fuel pump relay. Control of the valve is based upon engine temperature; the air by-pass channel is open when engine is cold and gradually closes as temperature rises. At predetermined temperatures, air by-pass channel is blocked and additional airflow stops. (Scheme 51)
Auxiliary Air Valve. Scheme 51
COLD START INJECTOR
Most models use a cold start injector which delivers additional fuel, and a start injector time switch which controls operation of the cold start injector. Some models use an Idle Speed Control (ISC) valve, while others use an Auxiliary Air Valve (AAV) to provide additional air during cold engine starts and warm-up.
The start injector time switch limits cold start injection to 1-12 seconds, depending upon engine coolant temperature. When engine coolant temperature rises above a specified point, bi-metallic contact breaks ground circuit of cold start injector and cold start enrichment is by-passed.
The ISC valve performs the same function as the auxiliary air valve. Mounted on the throttle body, the ISC is a solenoid-actuated valve which provides additional air during cold engine operation. It also maintains idle speed during air conditioner operation. The ISC is controlled directly by the ECU.
IDLE ADJUSTMENTS
Note. For all on-vehicle adjustments not covered, see TUNE-UP article in the TUNE-UP section.
See the appropriate 4-CYL TUNE-UP or 6-CYL TUNE-UP article in ENGINE PERFORMANCE section, and TCCS SYSTEM article in the COMPUTER ENG CONTROLS section.
TESTING
Note. See TCCS SYSTEM article in the COMPUTER ENG CONTROLS section.
Do not attempt to test ECU as permanent damage could result. It is possible to check wires for continuity. The ECU should only by judged faulty after compression is checked, ignition system has been tested and found problem-free, and all other fuel injection components have been thoroughly tested (including wiring).
Note. AFC electrical systems can be checked by using Electronic Fuel Injection testers prescribed by the manufacturer. Instructions for use of testers must be followed carefully to prevent damage to system.
FUEL INJECTORS & RESISTORS
- Connect tachometer to engine. Start engine and run at idle. Remove harness connector from injectors one at a time. Engine idle speed should drop 100-300 RPM as each injector is disconnected. If engine idle speed does not drop, check the wiring connector, injector resistance or injection signal from the computer.
- Disconnect electrical connector from each injector. Measure injector resistance. See INJECTOR RESISTANCE SPECIFICATIONS table. If injector is not to specification, replace injector. INJECTOR RESISTANCE SPECIFICATIONS Application Ohms Camry & Celica (3S-FE Eng.) 1.6 Celica (3S-GE Eng.) 13.8 Corolla FX-16 & Supra 1.8-3.4 MR2, Pickup/4Runner & Van 1.5-3
- Disconnect resistor block. Measure resistance between terminal "B" and to any other terminal. If reading between each terminals is not 2-3 ohms, replace resistor block.
FUEL PRESSURE
| CAUTION | Constant fuel pressure is maintained in fuel lines and component parts at all times. Relieve pressure before attempting to open system for testing. Do not allow fuel to flow onto engine or electrical parts or allow an open flame in area while testing fuel system components. |
- Disconnect negative battery cable. Unplug cold start injector electrical connector. Place container under fuel rail at union bolt of cold start injector hose.
- Remove union bolt and drain fuel rail. Remove cold start injector hose from union bolt and install fuel pressure gauge with hose to union bolt. Install gauge and bolt to fuel rail with a gasket on each side of gauge fitting.
- Connect battery cable and start engine. Disconnect vacuum line from fuel pressure regulator and pinch line closed. Gauge reading should be 38-44 psi (2.7-3.1 kg/cm 2 ) on Camry and Celica with 3S-FE engine or 33-38 psi (2.3-2.7 kg/cm 2 ) on all other models. If pressure is too high, replace fuel pressure regulator; if too low, check fuel system for leaks.
- With engine idling, connect vacuum line to pressure regulator. Pressure reading should decrease to 35 psi (2.4 kg/cm 2 ) on Camry and Celica with 3S-FE engine or 28 psi (2.0 kg/cm 2 ) on all other models. If not, replace fuel pressure regulator. Stop engine. If pressure drops quickly, check fuel pump, pressure regulator, and injectors.
FUEL PUMP CIRCUIT
- Turn ignition on. Remove cap from fuel pump test connector. Using a jumper wire, jump terminals Fp and AB of connector. Connector is located below airflow meter on Camry, MR2 and Van models. On Celica models it is located near brake booster. On FWD Corolla and FX-16 models it is near wiper motor. On Cressida, Pickup, Supra and 4Runner models it is near relay block No. 2.
- Fuel pressure should be felt at cold start injector hose and noise of fuel returning to tank should be heard at fuel pressure regulator.
- Remove jumper wire, install connector cap and turn ignition off. If none of the above conditions were met, check fusible link, engine fuse, fuel injection fuse, circuit opening relay, fuel pump, and all electrical connections. On Supra models, check fuel pump resistor for 7 ohms resistance. Replace resistor if necessary.
Remove air cleaner upper cover. Heat the intake air temperature sensor using heat lamp or heat gun. Using an ohmmeter, check resistance between terminals "THA" and "E2". If resistance is not within specifications shown in AIR TEMPERATURE SENSOR SPECIFICATIONS table, replace airflow meter.
| Air Temperature | Resistance (Ohms) |
|---|---|
| 4°F (-20°C) | 13,600-18,400 |
| 68°F (20°C) | 2205-2695 |
| 140°F (60°C) | 493-667 |
AIR TEMPERATURE SENSOR SPECIFICATIONS
AIRFLOW METER POTENTIOMETER
With ignition off, remove connector and check resistance between terminals. If resistance is not within specifications given in AIRFLOW METER SPECIFICATIONS table, replace airflow meter assembly.
| Application Terminal | Resistance (Ohms) | ||
|---|---|---|---|
| Except Supra | |||
| E2-Vs | (1) (2) 20-400 | ||
| E2-Vc | 100-400 | ||
| E2-Vb | |||
| FX-16, MR2 & Van Only | 200-400 | ||
| E1-Fc | Infinity at Close | ||
| Supra | |||
| Non-Turbo | |||
| E2-Vs | 20-600 | ||
| E2-Vc | 200-400 | ||
| E1-Fc | Infinity at Close | ||
| Turbo | |||
| Vs-E1 | Infinity | ||
| E1-Ks | 5000-10,000 | ||
| Vc-E1 | 10000-15,000 | ||
| E1-Vc | 5000-10,000 | ||
| (1) 200-600 ohms on Celica. (2) Up to 1000-3000 ohms in open position. | |||
| (1) | 200-600 ohms on Celica. |
| (2) | Up to 1000-3000 ohms in open position. |
AIRFLOW METER SPECIFICATIONS
Ensure engine is cold, then start engine. Pinch rubber hose between air valve and throttle chamber. Engine speed should decrease. After engine reaches operating temperature, pinch hose again. Engine speed should not decrease more than 50 RPM. If valve does not operate as outlined, replace auxiliary air valve.
Cressida
See TCCS SYSTEM article in the ENGINE PERFORMANCE section.
Supra
See TCCS SYSTEM article in the ENGINE PERFORMANCE section.
Note. To avoid damage to injector, perform this test within the shortest possible time.
- Disconnect negative battery cable and cold start injector connector. Remove cold start injector (with fuel supply connected) and place over glass container.
- Connect battery power to injector terminals. Fuel should spray from injector. If not, replace cold start injector.
- Disconnect test harness from cold start injector and check for fuel leakage from injector. Maximum leakage is less than one drop of fuel per minute. Resistance between cold start injector terminals should be 3-5 ohms.
COLD START INJECTOR TIME SWITCH
Connect ohmmeter leads to both terminals of switch. (Scheme 52)and (Scheme 53). Readings should be as specified for corresponding temperatures. See COLD START INJECTOR TIME SWITCH RESISTANCE table. If not, replace switch.
| Terminals | Resistance (Ohms) | |
|---|---|---|
| STA to STJ | ||
| Below 86°F (30°C) | 20-40 | |
| Above 104°F (40°C) | 40-60 | |
| STA to Ground | 20-80 | |
COLD START INJECTOR TIME SWITCH RESISTANCE
Location of Cold Start Injector Time Switch Terminal. Scheme 52
Cold Start Injector Time Switch Terminal Schematic. Scheme 53
Connect ohmmeter leads to both terminals of sensor. Readings should be as specified for corresponding temperatures. See COOLANT TEMPERATURE SENSOR RESISTANCE table. If not, replace coolant temperature sensor.
| Temperature °F (°C) | Resistance (Ohms) |
|---|---|
| 4°F (-20°C) | 14,600-17,800 |
| 68 (20) | 2250-2650 |
| 176 (80) | 290-350 |
COOLANT TEMPERATURE SENSOR RESISTANCE
IDLE SPEED CONTROL (ISC) VALVE (CAMRY, CRESSIDA, MR2, SUPRA & VAN)
The ISC performs the same function as the auxiliary air valve on other vehicles. It controls airflow through the throttle body air by-pass passage to maintain a fast idle speed when engine is cold. It also provides by-pass air to maintain idle speed after engine warm-up and during air conditioner operation.
4WD ENRICHMENT SYSTEM (TRUCK & 4RUNNER)
During 4WD operation it is necessary to richen the fuel mixture to compensate for engine load. This is accomplished by the use of a 4WD indicator switch, the ECU and a Vacuum Switching Valve (VSV).
When the vehicle is shifted into 4WD mode, the 4WD indicator switch is closed, sending a signal to the ECU. The ECU signals VSV to cut vacuum signal to fuel pressure regulator.
AUTO. TRANS. ENRICHMENT
When an auto. trans. is shifted into Drive, it is necessary to richen the fuel mixture to compensate for the engine load produced by the torque converter.
This is accomplished by the use of the neutral safety switch and the ECU. When the transmission is shifted to Drive, the neutral safety switch provides a signal to the ECU which in turn makes adjustments to richen air/fuel mixture.
FUEL ENRICHMENT SYSTEM (MR2 & SUPRA)
Because of the added engine load which occurs during A/C or high temperature operation, it is necessary to richen the fuel mixture. The ECU controls a VSV, which cuts off the intake manifold vacuum signal to the fuel pressure regulator. This increases fuel pressure at the injectors.
EGR VSV (SUPRA & CRESSIDA)
Controlled by the ECU, the EGR VSV opens and closes the vacuum signal to the EGR valve in accordance to engine load.
REMOVAL & INSTALLATION
| CAUTION | The fuel injection system maintains constant fuel pressure in fuel lines and component parts at all times. Always relieve fuel pressure before attempting to open system for testing or replacement of components. Do not allow fuel to flow onto engine or electrical parts. Do not allow open flame or sparks in area while servicing components. Disconnect negative battery cable before disconnecting any electrical component. |
Disconnect negative battery cable. Clear area for access to ECU. Disconnect electrical connector lock lever (if used) and carefully remove connector. Remove ECU retaining screws and remove ECU. To install, reverse removal procedure.
Disconnect negative battery cable. Disconnect air ducts and hoses connecting air cleaner and airflow meter. Remove air cleaner cover, if required. Remove airflow meter retaining bolts. Unplug airflow meter electrical connector and remove airflow meter. To install, reverse removal procedure.
- Disconnect negative battery cable. Unplug TPS electrical connector. Remove 2 screws securing TPS to housing. Remove by slowly pulling sensor off throttle shaft.
- To install, reverse removal procedure. Make sure sensor is aligned on throttle shaft and after replacement, perform TPS adjustment. See «ADJUSTMENTS»(/toyota/mr2/w10-1984-1990/remont/testing-diagnostics/#fuel-injection-system-bosch-afc) .
Disconnect negative battery cable and remove electrical connector from cold start injector. Relieve fuel system pressure and remove fuel supply line from injector. Remove injector retaining bolts and remove injector. To install, reverse removal procedure.
Note. Replacement of auxiliary air valve requires that immediate replacement be available or cooling system be drained to below level of valve.
Disconnect negative battery cable and remove electrical connector from air valve. Drain engine coolant, if required. Remove air hoses and coolant hoses (if equipped). Remove retaining bolts and remove air valve. To install, reverse removal procedure.
Note. Replacement of temperature sensor requires immediate replacement be available or cooling system be drained below level of sensor.
Disconnect negative battery cable and remove electrical connector from coolant sensor. Drain engine coolant, if required. Remove sensor. To install, reverse removal procedure.
THERMO TIME SWITCH
Note. Thermo time switch removal should be done only when engine is cold. Removal of switch requires having replacement switch ready for immediate installation or cooling system be drained below level of switch.
Disconnect negative battery cable and electrical connector from switch. Drain cooling system as required. Remove switch. To install, reverse removal procedure.
Disconnect negative battery cable and relieve fuel system pressure. Disconnect fuel lines and vacuum line at regulator. Remove pressure regulator. To install, reverse removal procedure.
Removal
- Release fuel system pressure and disconnect negative battery cable. Drain cooling system. Clear fuel rail and intake air chamber by disconnecting all air hoses, coolant hoses, vacuum hoses, and fuel hoses.
- Remove EGR valve and pipe and intake air duct. Remove intake air chamber and support bracket. Disconnect fuel injection wiring harness from all connectors near fuel rail and place harness on top of engine.
- Remove fuel rail retaining bolts. Remove fuel rail, injectors and fuel pressure regulator as an assembly.
- Separate fuel injectors from fuel rail by pulling injectors. Discard sealing grommet and "O" ring. Remove insulators from injector holes in intake manifold.
Installation
- To install, reverse removal procedure. Install new insulators in injector holes in intake manifold. Install new grommets and "O" rings on fuel injectors.
- Coat grommets and "O" rings with gasoline and push injectors onto fuel rail. Coat insulators and injector tips with gasoline prior to installation of injectors. Ensure injectors rotate freely.
EFI/TCCS Wiring Diagram (Camry). Scheme 54
EFI/TCCS Wiring Diagram (Celica - W/3S-FE Engine). Scheme 55
EFI/TCCS Wiring Diagram (Celica - W/3S-GE Engine). Scheme 56
EFI/TCCS Wiring Diagram (Corolla FWD - W/4A-GE Engine). Scheme 57
EFI/TCCS Wiring Diagram (Corolla RWD - W/4A-GE Engine). Scheme 58
EFI/TCCS Wiring Diagram (Cressida). Scheme 59
EFI/TCCS Wiring Diagram (MR2). Scheme 60
EFI/TCCS Wiring Diagram (Pickup & 4Runner). Scheme 61
EFI/TCCS Wiring Diagram (Supra - W/7M-GE). Scheme 62
EFI/TCCS Wiring Diagram (Supra - W/7M-GTE Engine). Scheme 63
EFI/TCCS Wiring Diagram (Van). Scheme 64
See also:
• ADJUSTMENTS