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1986 CitroŽn BX GTi article about electronic fuel injection from le Double Chevron 85

The BX 19 GTi has a Bosch LE-3 Jetronic electronic petrol injection system which powers its 1905 cc engine (125 hp DIN at 5500 rpm); it provides flexibility at all speeds (17.8 m.kg torque at 4500 rpm).

As we know, a petrol engine operates by the explosion, in its combustion chambers, of a mixture of air and petrol, compressed by the pistons.

Good combustion depends upon the precision of the blending of the air and the petrol. The theoretically perfect proportioning to obtain complete combustion is 1 gram of petrol for 15 grams of air. This is the stoichiometric ratio: 1/15.

To obtain more power, it is necessary to enrich the mixture with fuel (1/12.5):for better efficiency (burn less at equal output), it is necessary to make the mixture leaner (1/18).

This gaseous mixture can be made by a carburettor or by injection.

The 1905 cc electronic petrol injection engine of the BX 19 GTi

Operating principle of electronic fuel injection system

1 Petrol tank
2 electric pump
3 filter
4 injector
5 pressure regulator
6 air filter
7 air temperature sensor
8 airflow meter
9‚airflow meter bypass to regulate mixture
10 screw to regulate idle
11 throttle spring switch
12 supplementary air control
13 battery
14 ignition starting switch
15 relay
16 electronic computer
17 distribution
18 water temperature sensor

In an injection engine, each cylinder has an injector which directly sprays the petrol into the intake valve, at the exact instant and in the exact quantity necessary.
This is why injection is the fuel supply system best fitted for optimized proportioning, homogeneous proportioning with equal distribution among the cylinders, cold start-up with fast turnover, good filling at high engine speed.
Injection provides increased engine performance by improving the filling with air (elimination of the choke formed by the carburettor nozzle), a reduction in the specific consumption of fuel and in the exhaust gas proportion of carbon monoxide and unburnt hydrocarbons due to more accurate proportioning of the fuel, quieter engine operation and increased flexibility due to uniform combustion in the various cylinders, and automation of the activating of the engine when cold and when hot.

In the type of injection provided by the BX 19 GTi's Jetronic LE-3 , the quantity of air sucked in is the most accurate proportioning reference for specifying the quantity of petrol necessary for good combustion.
An electronic computer receives accurate and instantaneous information concerning the quantity and temperature of the air sucked in, the turning rate and the engine load condition, the cooling water temperature and the beginning of injection. By processing this data, the computer accurately determines the quantity of petrol which is strictly necessary for the engine at a given moment and it actuates and controls the precise duration of opening of the injectors.

Electronic injection comprises three separate circuits: - petrol, air, electronics.
The petrol circuit: The petrol is routed from the tank to an injector array by an electric pump. In this array, a regulator keeps the petrol pressure substantially constant. The electronically controlled injectors spray the petrol upline from the intake valves. Their flow rate depends only upon their opening time. When the engine is cold, the mixture is enriched by a longer injector opening time.
The air circuit: The air sucked in, coming from the air filter, crosses the airflow meter and the butterfly valve and then comes to the intake manifold each conduit of which is connected to a cylinder. The airflow meter sends a voltage signal to the computer (which will determine the opening time of the injectors, therefore the quantity of petrol), and this signal varies as a function of the quantity of air sucked in by the engine.
It has an air temperature probe on a by-pass circuit for regulating the mixture on idle. It brings the petrol pump into the circuit. Based upon the temperature of the engine, an additional air command supplies extra air during the engine heat-up phase.
The electronic circuit: The electronic computer receives information concerning the quantity of air sucked in by the engine, the cooling water temperature, the position of the air valve, the start-up phase, plus information concerning engine speed and the beginning of injection. It processes this data and instantly and accurately determines the quantity of petrol necessary in each cylinder at moment M, then, by electric pulses, controls the exact opening time of the solenoid injectors.

Fuel supply system of the BX19GTi. The computer, built into the flow meter housing (to the right) in the engine compartment, is cooled by fresh air circulating in the flow meter.

© 1986 le Double Chevron/2013 CitroŽnŽt