1979 Citroen CX engine

Downloaded from www.Manualslib.com manuals search engine ELECTRONIC FUEL INJECTION
OPERATION No MA. IE. 144-00 : <:hnrcrctwistics o/ the H I,-]c~trouic’a clcctrovic Op. MA. IE. 144-00 1
fuel iujrctian swtem.
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a L- JETRONIC H
System

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OPERATION No MA.IE. 144-00 : Chtiractcristics o/ the e 1,-Jc,tror,ic H clcctroltic
fire1 injc ctiwt systettt.
((L-JETRONIC,,
The H L-Jetronic 1) system is’an intermittent low-pressure injection system which injects petrol into the inlet
manifold.
The system measures the quantity of air drawn in by the engine. which is the main parameter for calculating
the amount of fuel. to be injected. The metering of the fuel is carried out by electro-magnetically triggered
injectors. These are under constant fuel pressure. The quantity of fuel injected is proportional to the duration
of injection. which in turn is optimally determined for any given engin& operating condition by an electronic
control unit ( E.C.U. ) from information supplied by several electric sensors.
One of the principal contributions of the H L-Jetronic H system is the reduction in the level of pollution of the
exhaust emissions.
The (( L-Jetronic v system is made up of the following components :
1
: Electric fuel pump
2 : Fuel filter
3 : Thermal switch
4 :, Double relay
5 : Electronic control unit ( E.C.U. )
6 : Supplementary air control
7 : Pressure regulator
8 : Injectors
9 : Cold-start injector
10. Idling speed adjustment screw
11 : Air-flow sensor ( with incorporated air temperature sensor )
12 : Switch on throttle butterfly spindle
13 : Additional resistors for the injectors (8)

Downloaded from www.Manualslib.com manuals search engine OPERATION No MA. IE. 144-00 : Cbtirnctcristics oj ~hc /’ I,-jetrorlic )) rlectronic
/he1 iujcctim systvrn. Op. MA.IE. 144-00 3
GENERAL LAYOUT
L 14-19

Downloaded from www.Manualslib.com manuals search engine OPERATION No MA.IE. 144-00 : Chu~acte~istics of the (( L-Jetronic n electronic
fuel injectiari system Op. MA.IE. 144-00 5
-AIR INLET SYSTEM’
Air drawn in via air filter ( 1 ) passes through the air-flow sensor (2’), via butterfly ( 3) and arrives in the inlet
distribution chamber, each pipe of which (4) leads to a cylinder.
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Each cylinder has an electro-magnetic injector which is located very close to the inlet valve in order to improve
engine performance.
The supplementary air control (6) is located in parallel with the butterfly, and supplies the supplementary air
required by the engine to run smoothly when cold.
_ Once the engine has reached its normal running temperature, the idling speed air-flow is provided by a by-pass
valve
$ ( 5) which by-passes the butterfly as well.
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2
co
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$ It is important that the system be air-tight downstream from the air-flow sensor, so that no (( secondary )) air can
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2 be drawn in, which would falsify the air-volume reading.

Downloaded from www.Manualslib.com manuals search engine 6
OPERATION No MA.IE. 144 - 00 : Churacteristics o/ the H L-Jetronic )) electronic
/uel injectian .system. FUEL CIRCUIT
A multiple roller-valve pump ( 2 ) draws the fuel from tank ( 1) and provides the injection pressure,
A filter (4) is fitted to the system.
In the fuel return pipe, the pressure regulator ( 3) maintains, under fuel load! a relative constant fuel pressure of
2 bars ( 29 ‘psi ).
The pressure regulator is connected to the intake manifold by a flexible pipe0 This allows the difference of
pressure betw.een the fuel and the inlet manifold to remain constant.Thus the necessary quantity of fuel delivered
by the injectors ( 5) depends exclusively on its duration of opening.

Downloaded from www.Manualslib.com manuals search engine OPERATION No MA.IE. 144-00 : ch arartcristics of the K L-Jetrouic )) elcctrcwic
juel ir2jcctirm system. / Op. MAalE. 144-00 7
FUEL CIRCUIT
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Downloaded from www.Manualslib.com manuals search engine 8 OPERATION No MA.IE. 144-00 : Characteristics of the (( L-Jetrovzic n electronic
fuel ivzjectian system. t
E;C.U.
( ELECTRONIC CONTROL UNIT )
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Downloaded from www.Manualslib.com manuals search engine OPEdATlON N- MA.IE. 144-00 : C1 3aractcJristics o/ the e L-Jetro~ic n elcctrorlir Op. MA.IE. 144-00 9
fuel injectian systwn. E.C.U; ( ELECTRONIC CONTROL UNIT )
Apart from three integrated circuits ( I.C. ) forming the main part of the E.C.U., there are in addition only a few
semi-conducting components condensers, calibrating resistors and filters so as to avoid.any interference.
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The function of the E.C.U. is ,to supply an impulse to the injectors, and to control their opening for a precisely
defined amount of time. The E.C.U. to this effect uses the information provided by all the engine sensors which
translate the operating conditions of the engine into electric impulses.
All the injectors are connected in parallel, and inject fuel simultaneously twice for each rotation of the camshaft
( therefore,twice for each engine cycle ), injecting half the quantity of fuel required each time With this system
it is not necessary for the camshaft angle to coincide with the beginning of injection point, which eliminates the
need for a generating switch incorporated in the distributor.
The injection impulse control is ensured by the distributor impulses. The distributor produces four impulses for
every operational cycle. Since injection only occurs twice in every cycle, the E.C.U. must divide the frequency
by 2.
The impulses coming from the distriLti, are transformated into square waves by the waveform shaper. Since
injection only occurs twice for each camshaft rotation, whereas the distributor provides 4 impulses in the same
amount of time, the frequency of the impulses must be divided by 2 in the frequency divider.
These signals are used to charge a condenser. The condenser discharge determines the beginning of injection
point; the position of the air-flow sensor flap ( which determines the quantity of air drawn in ) being the main
parameter for calculating the duration of injection.
At the multiplying stage of the E.C.U., various correction values ( full load and idling speed via throttle butterfly
spindle switch, engine temperature via the water temperature sensor, air temperature via the air-temperature sensor
located in the air-flow sensor ) are combined with the signals from the air-flow sensor and the injt,ztion frequency
in order to determine the injection duration which is transmitted to the injectors by way of impulses.
The time it takes for the injector needle to open and close depends on the battery voltage.
As the supply voltage increases, the injection duration increases.
The fact that the quantity of fuel injected depends
on the voltage is cancelled out by the fact that the injection duration is inversely proportional to the voltaqq,in the
E.C.U.
The final impulse determines the time during which the injectors are connected to earth ( injection duration ‘supplied
by the output stage ).