zx-04c.pdf

4C•1

Chapter 4 Part C: Fuel and exhaust systems -

multi-point fuel injection models

Contents

ACAV intake system (1998 cc 16-valve models) - general

information, removal and refitting 19

Accelerator cable - removal, refitting and adjustment 3

Accelerator pedal - removal and refitting 4

Air cleaner assembly and intake ducts - removal and refitting 2

Air cleaner filter element renewal See Chapter 1

Bosch Motronic M1.3 system components - removal and refitting ... 15

Bosch Motronic MP3.1 system components - removal and refitting .. 14

Bosch Motronic MP3.2 system components - removal and refitting .. 16

Bosch Motronic MP5.1 system components - removal and refitting .. 13

Exhaust manifold - removal and refitting

Fuel gauge sender unit - removal and refitting 9

Fuel injection system - depressurisation 7

Fuel injection system - testing and adjustment 11

Fuel injection systems - general information 6

Fuel pump - removal and refitting 8

Fuel tank - removal and refitting 10

General fuel system checks See Chapter 1

General information and precautions 1

Idle speed and mixture adjustment See Chapter 1

Inlet manifold - removal and refitting 18

Magneti Marelli 8P.20 system components - removal and refitting . 17

Throttle housing - removal and refitting

Exhaust system - general information, removal and refitting

Exhaust system check

See Chapter 1

Unleaded petrol - general information and usage

Fuel filter - renewal

See Chapter 1

Degrees of difficulty

Easy, suitable for

novice with little

experience

Fairly easy, suitable

for beginner with

some experience

Fairly difficult, suitable

for competent DIY

mechanic

Difficult, suitable for

experienced DIY

mechanic

Very difficult,

suitable for expert DIY

or professional

Specifications

System type

1761 cc (LFZ engine) models Bosch Motronic MP5.1

1905 cc non-catalyst (D6E engine) models Bosch Motronic MP3.1

1905 cc catalyst (DKZ engine) models Bosch Motronic M1.3

1998 cc 8-valve (RFX engine) models Magneti Marelli 8P.20

1998 cc 16-valve (RFY engine) models Bosch Motronic MP3.2

Note: Refer to Chapter 2B for further information on engine code identification

Fuel system data

Fuel pump type

Electric, immersed in tank

Fuel pump regulated constant pressure (at specified idle speed):

Bosch Motronic systems

2.5 to 3.0 bars (depending on system)

Magneti Marelli system

2.0 bars

Specified idle speed:

1905 cc models

850 ± 50 rpm (adjustable via screw on the throttle housing)

All other models

850 ± 50 rpm (not adjustable -controlled by ECU)

Idle mixture CO content:

1905 cc non-catalyst (D6E engine) models

1.0 to 2.0 % (adjustable via screw on mixture adjustment -

potentiometer)

1905 cc catalyst (DKZ engine) models, and all other models

Less than 1.0 % (not adjustable- controlled by ECU)

Recommended fuel

Minimum octane rating:

1905 cc non-catalyst (D6E engine) models

95 RON unleaded (UK unleaded premium) or

97 RON leaded (UK "4-star")

1905 cc catalyst (DKZ engine) models, and all other models

95 RON unleaded (UK unleaded premium).

Leaded fuel must not be used

4C•2 Fuel and exhaust systems - multi-point fuel injection models

Torque wrench settings

ibf ft

Inlet manifold nuts

Exhaust manifold nuts

Exhaust system fasteners:

Front pipe-to-manifold nuts

Clamping ring nut(s):

Clamps secured with one bolt

Clamps secured with two bolts

Warning: Many of the procedures

in this Chapter require the

removal of fuel lines and

connections, which may result in some fuel

spillage. Before carrying out any operation

on the fuel system, refer to the precautions

given in "Safety first!" at the beginning of

this manual, and follow them implicitly.

Petrol is a highly-dangerous and volatile

liquid, and the precautions necessary when

handling it cannot be overstressed.

Note: Residual pressure will remain in the fuel

lines long after the vehicle was last used. When

disconnecting any fuel line, first depressurise

the fuel system as described in Section 7.

cleaner-to-throttle housing duct. Slacken the

duct retaining clips, then disconnect it from

the air cleaner and throttle housing, and

remove it from the vehicle (see illustrations).

Where necessary, recover the rubber sealing

ring from the throttle housing.

2 Release the two retaining clips, then

slacken and remove the two retaining screws

from the front of the cylinder head cover, and

remove the air cleaner element cover from the

head. Withdraw the air cleaner element.

3 To remove the intake duct, undo the bolt

securing the rear section of the duct to the

end of the cylinder head, then slacken the

retaining clip and disconnect the duct from

the cylinder head cover. Undo the nut

securing the front of the duct to the left-hand

wing valance, and manoeuvre the duct out of

the engine compartment (see illustration).

1905 cc models

4 Slacken the retaining clips, and disconnect

the intake duct and throttle housing duct from

the air cleaner (see illustration).

5 Slacken and remove the bolt securing the

air cleaner right-hand mounting bracket to the

rear of the cylinder head, and the two nuts

securing the housing to its left-hand mounting

bracket. Lift the air cleaner housing out of the

engine compartment (see illustrations).

6 To remove the intake duct, undo the nut(s)

securing the front of the duct to the left-hand

wing valance, then undo the nut securing the

duct to its mounting bracket (where fitted).

Disconnect the duct from the air cleaner

housing, if not already having done so, and

remove it from the vehicle.

7 On models without a catalytic converter

(Bosch Motronic MP3.1 system), to remove

the air cleaner-to-throttle housing duct, first

1 General information and

precautions

The fuel supply system consists of a fuel

tank (which is mounted under the rear of the

car, with an electric fuel pump immersed in it),

a fuel filter, fuel feed and return lines. The fuel

pump supplies fuel to the fuel rail, which acts

as a reservoir for the four fuel injectors which

inject fuel into the inlet tracts. The fuel filter

incorporated in the feed line from the pump to

the fuel rail ensures that the fuel supplied to

the injectors is clean.

Refer to Section 6 for further information on

the operation of each fuel injection system,

and to Section 21 for information on the

exhaust system. Throughout this Section, it is

also occasionally necessary to identify

vehicles by their engine codes rather than by

engine capacity alone. Refer to the relevant

Part of Chapter 2 for further information on

engine code identification.

2 Air cleaner assembly and intake

ducts - removal and refitting

Removal

1761 cc and 1998 cc 8-valve models

1 Slacken the retaining clip, and disconnect

the breather hose(s) from the side of the air

2.1a On 1761 cc and 1998 cc 8-valve

models, slacken the clips and disconnect

the hose(s) from the air cleaner-to-throttle

body duct...

2.1b ... then slacken the duct retaining

clips ...

2.4 On 1905 cc models, slacken the

retaining clips and disconnect the intake

and throttle housing ducts from the air

cleaner...

2.1c ... and remove the duct from the

engine compartment

2.3 Intake duct front retaining nut

Fuel and exhaust systems - multi-point fuel injection models 4C•3

of the system operates as follows.

2 The fuel pump (which is immersed in the

fuel tank) supplies fuel from the tank to the

fuel rail, via a filter mounted underneath the

rear of the vehicle. Fuel supply pressure is

controlled by the pressure regulator in the fuel

rail. When the optimum operating pressure of

the fuel system is exceeded, the regulator

allows excess fuel to return to the tank.

3 The electrical control system consists of the

ECU, along with the following sensors:

(a) Throttle potentiometer - informs the ECU

of the throttle position, and the rate of

throttle opening/closing.

(b) Coolant temperature sensor - informs the

ECU of engine temperature.

the ECU of the temperature of the air

passing through the throttle housing.

(d) Lambda sensor - informs the ECU of the

oxygen content of the exhaust gases

(explained in greater detail in Part D of

this Chapter).

(e) Crankshaft sensor - informs the ECU of

the crankshaft position and speed of

rotation.

(f) Manifold Absolute Pressure (MAP) sensor

- informs the ECU of the load on the

engine (expressed in terms of inlet

manifold vacuum).

(g) Vehicle speed sensor - informs the ECU

of the vehicle speed.

4 All the above signals are analysed by the ECU,

and it selects the fuelling response appropriate to

those values. The ECU controls the fuel injectors

(varying the pulse width - the length of time the

injectors are held open - to provide a richer or

weaker mixture, as appropriate). The mixture is

constantly varied by the ECU, to provide the best

setting for cranking, starting (with either a hot or

cold engine), warm-up, idle, cruising, and

acceleration.

5 The ECU also has full control over the

engine idle speed, via an auxiliary air valve

which bypasses the throttle valve. When the

throttle valve is closed, the ECU controls the

opening of the valve, which in turn regulates

the amount of air entering the manifold, and

so controls the idle speed.

6 The ECU also controls the exhaust and

evaporative emission control systems, which

are described in detail in Part D of this

Chapter.

7 An electric heating element is fitted to the

throttle housing; the heater is supplied with

current by the ECU, and warms the throttle

housing on cold starts to prevent possible

icing of the throttle valve.

8 If there is an abnormality in any of the

readings obtained from either the coolant

temperature sensor, the intake air

temperature sensor or the lambda sensor, the

ECU enters its back-up mode. In this event, it

ignores the abnormal sensor signal, and

assumes a pre-programmed value which will

allow the engine to continue running (albeit at

reduced efficiency). If the ECU enters this

back-up mode, the warning light on the

2.5a ... then undo the retaining bolt

(arrowed)...

2.5b ... and the two retaining nuts

(locations arrowed), then remove the air

cleaner housing

disconnect the wiring connector from the

intake air temperature sensor. Slacken the

retaining clip, and disconnect the vacuum

pipe from the front of the duct. Slacken the

clips, disconnect the duct from the air cleaner

and throttle housings, and remove the duct.

Recover the rubber sealing ring from the

throttle housing.

8 On models with a catalytic converter

(Bosch Motronic M1.3 system), the air

cleaner-to-throttle housing duct is in two

sections, with the airflow meter situated in the

middle. Each section can be removed once its

retaining clips have been slackened, noting

that, in the case of the front duct section, it

will also be necessary to disconnect the

vacuum pipe.

1998 cc 16-valve models

9 Slacken the retaining clip, and disconnect

the air cleaner-to-throttle housing duct from

the throttle housing. Recover the rubber

sealing ring. Release the retaining clips, and

disconnect the breather hose(s) from the duct.

10 Apply the handbrake, then jack up the

front of the vehicle and support it on axle

stands.

11 From underneath the vehicle, slacken and

remove the retaining nuts securing the

resonator chamber to the side of the air

cleaner housing, and remove the chamber.

12 Undo the air cleaner housing retaining

bolt(s), and remove the housing and duct

assembly from underneath the vehicle.

Refitting

13 Refitting is a reversal of the removal

procedure, ensuring that all hoses are

properly reconnected, and that all ducts are

correctly seated and securely held by their

retaining clips.

4 Accelerator pedal -

removal and refitting

Refer to Chapter 4A, Section 8.

5 Unleaded petrol - general

information and usage

Note: The information given in this Chapter is

correct at the time of writing. If updated

information is thought to be required, check

with a Citroen dealer. If travelling abroad,

consult one of the motoring organisations (or a

similar authority) for advice on the fuel available.

1 The fuel recommended by Citroen is given

in the Specifications Section of this Chapter,

followed by the equivalent petrol currently on

sale in the UK.

2 All Citroen ZX multi-point injection models

are designed to run on fuel with a minimum

octane rating of 95 (RON). With the exception

of those 1905 cc models without a catalytic

converter (Bosch Motronic MP3.1 system), all

models have a catalytic converter, and so

must be run on unleaded fuel only. Under no

circumstances should leaded fuel (UK "4-star")

be used, as this may damage the converter.

However, 1905 cc models without a catalytic

converter can use either unleaded or leaded

fuel without modification or risk of damage.

3 Super unleaded petrol (98 octane) can also

be used in all models if wished, though there

is no advantage in doing so.

6 Fuel injection systems - general

information

Bosch Motronic MP5.1 system -

1761 cc models

1 The Bosch Motronic engine management

(fuel injection/ignition) system is fitted to all

1761 cc models. The system incorporates a

closed-loop catalytic converter and an

evaporative emission control system, and

complies with the very latest emission control

standards. Refer to Chapter 5 for information

on the ignition side of the system; the fuel side

3 Accelerator cable - removal,

refitting and adjustment

1 Refer to Chapter 4A, Section 7, substituting

"throttle housing" for all references to the

carburettor. On models with automatic

transmission, once the accelerator cable is

correctly adjusted, check the kickdown cable

adjustment as described in Chapter 7B.

4C•4 Fuel and exhaust systems - multi-point fuel injection models

1 The fuel system referred to in this Section is

defined as the tank-mounted fuel pump, the

fuel filter, the fuel injectors, the fuel rail and

the pressure regulator, and the metal pipes

and flexible hoses of the fuel lines between

these components. All these contain fuel

which will be under pressure while the engine

is running, and/or while the ignition is

switched on. The pressure will remain for

some time after the ignition has been

switched off, and it must be relieved in a

controlled fashion when any of these

components are disturbed for servicing work.

2 Disconnect the battery negative terminal.

3 Place a container beneath the

connection/union to be disconnected, and

have a large rag ready to soak up any

escaping fuel not being caught by the

container.

4 Slowly loosen the connection or union nut

to avoid a sudden release of pressure, and

position the rag around the connection, to

catch any fuel spray which may be expelled.

Once the pressure is released, disconnect the

fuel line. Plug the pipe ends, to minimise fuel

loss and prevent the entry of dirt into the fuel

system.

instrument panel will come on, and the

relevant fault code will be stored in the ECU

memory.

9 If the warning light comes on, the vehicle

should be taken to a Citroen dealer at the

earliest opportunity. A complete test of the

engine management system can then be

carried out, using a special electronic

diagnostic test unit which is simply plugged

into the system's diagnostic connector.

Bosch Motronic MP3.1 system -

1905 cc models without a catalytic

converter

10 The Bosch Motronic MP3.1 engine

management (fuel injection/ignition) system is

fitted to all 1905 cc models without a catalytic

converter (D6E engine). Refer to Chapter 5 for

information on the ignition side of the system.

11 The MP3.1 system is very similar in

operation to the MP5.1 system described

above, noting the following differences:

(a) On the MP3.1 system, there is no lambda

(oxygen) sensor or vehicle speed sensor.

The idle mixture (exhaust gas CO content)

can be manually adjusted via the mixture

adjustment potentiometer.

(b) The ECU has no control over the engine

idle speed; the idle speed is manually set

using a screw on the throttle housing. An

auxiliary air valve (not to be confused with

the idle speed control valve on the MP5.1

system) is incorporated in the system, but

this is used purely as an additional air

supply on cold starts and during the

warm-up period.

throttle housing. The engine coolant is

circulated around the housing, to warm

the housing after cold starts.

(d) There is no evaporative emission control

system.

Bosch Motronic Ml.3 system -

1905 cc models with a catalytic

converter

12 The Bosch Motronic M1.3 engine

management (fuel injection/ignition) system is

fitted to all 1905 cc models with a catalytic

converter (DKZ engine). Refer to Chapter 5 for

information on the ignition side of the system.

13 The M1.3 system is very similar in

operation to the MP5.1 system described

above, noting the following differences:

(a) On the M1.3 system, there is no vehicle

speed sensor or MAP sensor. In place of

the MAP sensor, an airflow meter is fitted

to the throttle housing intake duct, to

inform the ECU of the volume of air

passing through the duct and entering the

throttle housing.

(b) The ECU has no control over the engine

idle speed; the idle speed is manually set

using a screw on the throttle housing. An

auxiliary air valve (not to be confused with

the idle speed control valve on the MP5.1

system) is incorporated in the system, but

this is used purely as an additional air

supply on cold starts and during the

warm-up period.

throttle housing. The engine coolant is

circulated around the housing, to warm

the housing after cold starts.

Bosch Motronic MP3.2 system -

1998 cc 16-valve models

14 The Bosch Motronic MP3.2 engine

management (fuel injection/ignition) system is

fitted to all 1998 cc 16-valve models. Refer to

Chapter 5 for information on the ignition side

of the system.

15 The MP3.2 system is very similar in

operation to the MP5.1 system described

above, noting that, in addition to the sensors

listed, a camshaft position sensor is

incorporated into the system. The camshaft

position sensor is fitted to the left-hand end of

the cylinder head, directly over the top of the

inlet camshaft, and informs the ECU when

No 1 cylinder is at Top Dead Centre (TDC).

16 The MP3.2 system differs from all the

other fuel injection systems in that it is a

"sequential" system. This means that each of

the four fuel injectors is triggered individually,

just before the inlet valve on that particular

cylinder opens. This is in contrast to all other

systems, on which all four injectors are

triggered simultaneously; this happens once

for every revolution of the crankshaft.

Magneti Marelli 8P.20 system -

1998 cc 8-valve models

17 The Magneti Marelli 8P.20 engine

management (fuel injection/ignition) system is

fitted to all 1998 cc 8-valve models. Refer to

Chapter 5 for information on the ignition side

of the system.

18 The system is very similar in operation to

the Bosch MP5.1 system described above,

apart from the idle speed control system.

19 On the Magneti Marelli system, the idle

speed is controlled by the ECU via a stepper

motor fitted to the throttle housing. The motor

has a pushrod controlling the opening of an

air passage which bypasses the throttle valve.

When the throttle valve is closed, the ECU

controls the movement of the motor pushrod,

which regulates the amount of air which flows

through the throttle housing passage, so

controlling the idle speed. The bypass

passage is also used as an additional air

supply during cold starting.

8 Fuel pump -

removal and refitting

Note: Refer to the warning note in Section 1

before proceeding.

Removal

1 Disconnect the battery negative lead.

2 For access to the fuel pump, tilt or remove

the rear seats, as described in Chapter 11.

3 Using a screwdriver, carefully prise the

plastic access cover from the floor, to expose

the fuel pump (located under the right-hand

cover).

4 Disconnect the wiring connector from the

fuel pump, and tape the connector to the

vehicle body, to prevent it disappearing

behind the tank.

5 Mark the hoses for identification purposes,

then slacken the feed and return hose

retaining clips. Where the original crimped-

type Citroen hose clips are fitted, cut the clips

and discard them; use standard worm-drive

hose clips on refitting. Disconnect both hoses

from the top of the pump, and plug the hose

ends.

6 Noting the alignment marks on the tank,

pump cover and the locking ring, unscrew the

ring and remove it from the tank. This is best

accomplished by using a screwdriver on the

raised ribs of the locking ring, as follows.

Carefully tap the screwdriver to turn the ring

anti-clockwise until it can be unscrewed by

hand.

7 Displace the pump cover, then reach into the

tank and unclip the pump from the tank base.

Carefully lift the fuel pump assembly out of the

fuel tank, taking care not to damage the filter,

or to spill fuel onto the interior of the vehicle.

7 Fuel system - depressurisation

Note: Refer to the warning note in Section 1

before proceeding.

Warning: The following

procedure will merely relieve the

pressure in the fuel system -

remember that fuel will still be

present in the system components and

take precautions accordingly before

disconnecting any of them.

Fuel and exhaust systems - multi-point fuel injection models 4C•5

adjustment (exhaust gas CO level) nor the idle

speed are adjustable, and should either be

incorrect, a fault must be present in the fuel

injection system.

Recover the rubber sealing ring and discard it -

a new one must be used on refitting.

8 Note that the fuel pump is only available as

a complete assembly - no components are

available separately.

11 Fuel injection system -

testing and adjustment

Testing

1 If a fault appears in the fuel injection

system, first ensure that all the system wiring

connectors are securely connected and free

of corrosion. Ensure that the fault is not due to

poor maintenance; ie, check that the air

cleaner filter element is clean, the spark plugs

are in good condition and correctly gapped,

the cylinder compression pressures are

correct, the ignition timing is correct, and that

the engine breather hoses are clear and

undamaged, referring to Chapters 1, 2 and 5

for further information.

2 If these checks fail to reveal the cause of

the problem, the vehicle should be taken to a

suitably-equipped Citroen dealer for testing. A

wiring block connector is incorporated in the

engine management circuit, into which a

special electronic diagnostic tester can be

plugged; the connector is located inside either

the engine compartment junction box, or

directly in front of the box (see illustration) .

The tester will locate the fault quickly and

simply, alleviating the need to test all the

system components individually, which is a

time-consuming operation that carries a risk

of damaging the ECU.

12 Throttle housing -

removal and refitting

Refitting

9 Ensure the fuel pump pick-up filter is clean

and free of debris. Fit the new sealing ring to

the top of the fuel tank.

10 Carefully manoeuvre the pump assembly

into the fuel tank, and clip it into position in

the base of the tank.

11 Align the mark on the fuel pump cover

with the centre of the three alignment marks

on the fuel tank, then refit the locking ring.

Securely tighten the locking ring, and check

that the locking ring, pump cover and tank

marks are all correctly aligned.

12 Reconnect the feed and return hoses to

the top of the fuel pump, using the marks

made on removal to ensure they correctly

reconnected, and securely tighten their

retaining clips.

13 Reconnect the pump wiring connector.

14 Reconnect the battery negative terminal,

and start the engine. Check the fuel pump

feed and return hoses unions for signs of

leakage.

15 If all is well, refit the plastic access cover,

and tilt or refit the rear seat as described in

Chapter 11 (as applicable).

Removal

1 Disconnect the battery negative terminal.

1761 cc and 1998 cc 8-valve models

2 Remove the air cleaner-to-throttle housing

duct as described in Section 2.

3 Disconnect the accelerator inner cable from

the throttle cam, then withdraw the outer

cable from the mounting bracket, along with

its flat washer and spring clip (see

illustration) .

4 Depress the retaining clips, and disconnect

the wiring connectors from the throttle

potentiometer, the electric heating element,

the air temperature sensor and idle control

stepper

motor

(as

applicable)

(see

illustration) .

5 Release the retaining clips (where fitted),

and disconnect all the relevant vacuum and

breather hoses from the throttle housing (see

illustration) . Make identification marks on the

hoses, to ensure they are connected correctly

on refitting.

6 Slacken and remove the three retaining

screws, and remove the throttle housing from

Adjustment

3 On 1905 cc models without a catalytic

converter (Motronic MP3.1 system), both the

idle speed and idle mixture (exhaust gas CO

level) are adjustable. On 1905 cc models with

a catalytic converter (Motronic M1.3 system),

only the idle speed is adjustable (mixture

adjustment is not possible). Refer to Chapter

1 for information on adjustment procedures.

4 On all other models, experienced home

mechanics with a considerable amount of skill

and equipment (including a tachometer and

an accurately calibrated exhaust gas analyser)

may be able to check the exhaust CO level

and the idle speed. However, if these are

found to be in need of adjustment, the car

must be taken to a suitably-equipped Citroen

dealer for further testing. Neither the mixture

9 Fuel gauge sender unit -

removal and refitting

Refer to Chapter 4A, Section 5, noting that

there are no fuel pipe connections to the

sender unit.

10 Fuel tank -

removal and refitting

Refer to Chapter 4A, Section 6, noting that

it will be necessary to depressurise the fuel

system as the feed and return hoses are

disconnected (see Section 7). It will also be

necessary to disconnect the wiring connector

from the fuel pump before lowering the tank

out of position (see Section 8).

11.2 Diagnostic wiring connector located

in the engine compartment junction box

12.5 Throttle housing vacuum hoses

(arrowed) - 1761 cc model

12.3 Disconnecting the accelerator cable -

1998 cc 8-valve model

12.4 Throttle housing wiring connectors

(arrowed) -1761 cc model

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