The required amount of fuel is calculated by the processor unit based on information from various sensors. This unit also controls the idle speed, emission and ignition systems.
The fuel injection system allows precise control of the ratio of mixture components in all engine operating modes. This control is necessary to maintain the minimum level of harmful emissions in the exhaust gases and for the proper functioning of the catalytic converter. Additional advantages from the driver's point of view include lower fuel consumption and better vehicle control when the engine is running cold.
The operation of the system can be better understood by dividing it into two parts: the fuel supply and the control system.
Fuel supply
The system uses four fuel injectors, one per cylinder. The injectors are installed in the intake manifold. On early F7P engines (with 16 valves) with a catalytic converter, a separate cold-start injector delivers additional fuel when the starter is engaged and the coolant temperature is below 20°C. All injectors are fed from a common line, which also includes a fuel pressure regulator. Excess fuel is returned to the tank.
Control
The control subsystem consists of the injection system processor unit and associated sensors and drives. As mentioned earlier, the processor also controls the emission and ignition systems.
The processor unit is located in the engine compartment, in the right air intake box. (On models with air conditioning, the unit is located in the passenger compartment, under the glove compartment.) The unit receives signals from sensors that monitor the following parameters:
- Coolant temperature.
- Inlet air temperature.
- Engine speed (flywheel sensor).
- Speed of movement (speedometer cable sensor).
- Suction manifold pressure (pressure sensor).
- Throttle position (potentiometer).
- Oxygen in the exhaust gas (oxygen sensor).
- Power steering fluid pressure sensor (where it is applied).
On D-series and F3P engines, the processor unit also receives signals from the knock sensor, which is part of the ignition system and is described in Section 5C. The oxygen sensor is part of the exhaust gas aftertreatment system and is described in detail in Part E of this Section.
- The output signals from the processor unit control the following components:
- Fuel pump (via relay).
- Fuel injectors.
- Idle speed control valve.
- Solenoid valve of the fuel vapor extraction system.
- Ignition amplifier control unit.
- Air conditioning compressor relay (where it is applied).
The processor processes information from various sensors, determining the amount of fuel that should be injected for a particular engine operating mode at any given time. For this purpose, the intake air volume is calculated based on engine speed and throttle position information, with correction for intake air temperature. At maximum load and during warm-up, additional enrichment is provided. Correction is also performed when the battery voltage changes.
In no-load mode (the throttle lever presses the idle speed sensor), the processor stops fuel injection at engine speeds above idle. At idle, the engine speed is controlled by the computer, which sends a signal to the idle drive motor built into the throttle body. The engine opens or closes the throttle valve, constantly maintaining the idle speed regardless of engine temperature or additional load (generator, power steering pump, etc.). There is no need to periodically adjust the idle speed or mixture, even to compensate for engine wear. The system also has automatic adjustment to altitude.
All later models are equipped with an inertia fuel cut-off switch (see Chapter 15), which interrupts the fuel supply in the event of a vehicle collision. The engine cannot be started if the system is activated. The switch needs to be reset.
You can find the original at this link: RENAULTBOOK
Troubleshooting
In the event of a malfunction, limited diagnostics are available to the car owner. Renault technicians use specialized equipment that allows them to quickly and accurately identify faults. First, it is necessary to inspect the fuel filter, check the condition of the connectors and vacuum hoses. Also remember that improper adjustment of the throttle cable can affect the operation of the fuel injection system, especially at idle.
If you suspect a fault with one of the sensors or the processor unit, we recommend contacting your Renault dealer or other specialist.