Ford Orion. Manual — part 44

General

ECU (Electronic Control Unit)

1 This component is the heart of the entire
engine management system, controlling the
fuel injection, ignition and emissions control
systems. It also controls sub-systems such as
the air conditioning and automatic
transmission, where appropriate. Refer to
Section 2 of this Chapter for an illustration of
how it works.

Air mass meter

2 The air mass meter fitted to models
equipped with Sequential Electronic Fuel
Injection (SEFI) is based on a “hot-wire”
system, sending the ECU a constantly-varying
(analogue) voltage signal corresponding to the
mass of air passing into the engine. Since air
mass varies with temperature (cold air being
denser than warm), measuring air mass
provides the ECU with a very accurate means
of determining the correct amount of fuel
required to achieve the ideal air/fuel mixture
ratio.

Crankshaft speed/position sensor

3 This is an inductive pulse generator bolted
(in a separate bracket) to the cylinder
block/crankcase, to scan the ridges between
36 holes machined in the inboard (right-hand)
face of the flywheel/driveplate. As each ridge
passes the sensor tip, a signal is generated,
which is used by the ECU to determine engine
speed.
4 The ridge between the 35th and 36th holes
(corresponding to 90º BTDC) is missing - this
step in the incoming signals is used by the
ECU to determine crankshaft (ie, piston)
position.

Camshaft position sensor

5 This is bolted to the rear left-hand end of
the cylinder head on Zetec engines, to register
with a lobe on the inlet camshaft. It functions
in the same way as the crankshaft
speed/position sensor, producing a series of
pulses (corresponding to No 1 cylinder at 46º
ATDC); this gives the ECU a reference point,
to enable it to determine the firing order, and
operate the injectors in the appropriate
sequence.

Coolant temperature sensor

6 This component is an NTC (Negative
Temperature Coefficient) thermistor - that is, a
semi-conductor whose electrical resistance
decreases as its temperature increases. It
provides the ECU with a constantly-varying
(analogue) voltage signal, corresponding to
the temperature of the engine coolant. This is
used to refine the calculations made by the
ECU, when determining the correct amount of
fuel required to achieve the ideal air/fuel
mixture ratio.

Inlet air temperature sensor

7 This component is also an NTC thermistor -
see the previous paragraph - providing the
ECU with a signal corresponding to the
temperature of air passing into the engine.

This is used to refine the calculations made by
the ECU, when determining the correct
amount of fuel required to achieve the ideal
air/fuel mixture ratio.

Throttle position sensor

8 This is mounted on the end of the throttle
valve spindle, to provide the ECU with a
constantly-varying (analogue) voltage signal
corresponding to the throttle opening. This
allows the ECU to register the driver’s input
when determining the amount of fuel required
by the engine.

Vehicle speed sensor

9 This component is a Hall-effect generator,
mounted on the transmission’s speedometer
drive. It supplies the ECU with a series of
pulses corresponding to the vehicle’s road
speed, enabling the ECU to control features
such as the fuel shut-off on the overrun, and
to provide information for the trip computer,
adaptive damping and cruise control systems
(where fitted).

Manifold absolute pressure (MAP)
sensor

10 The manifold absolute pressure sensor
measures inlet manifold vacuum, and supplies
this information to the ECU for calculation of
engine load at any given throttle position.

Power steering pressure switch

11 This is a pressure-operated switch,
screwed into the power steering system’s
high-pressure pipe. Its contacts are normally
closed, opening when the system reaches the
specified pressure - on receiving this signal,
the ECU increases the idle speed, to
compensate for the additional load on the
engine.

Oxygen sensor

12 The oxygen sensor in the exhaust system
provides the ECU with constant feedback -
“closed-loop” control - which enables it to
adjust the mixture to provide the best possible
conditions for the catalytic converter to
operate.
13 The sensor has a built-in heating element
which is controlled by the ECU, in order to
bring the sensor’s tip to an efficient operating
temperature as rapidly as possible. The
sensor’s tip is sensitive to oxygen, and sends
the ECU a varying voltage depending on the
amount of oxygen in the exhaust gases; if the
intake air/fuel mixture is too rich, the sensor
sends a high-voltage signal. The voltage falls
as the mixture weakens. Peak conversion
efficiency of all major pollutants occurs if the
intake air/fuel mixture is maintained at the
chemically-correct ratio for the complete
combustion of petrol - 14.7 parts (by weight)
of air to 1 part of fuel (the `stoichiometric’
ratio). The sensor output voltage alters in a
large step at this point, the ECU using the
signal change as a reference point, and
correcting the intake air/fuel mixture
accordingly by altering the fuel injector pulse
width (injector opening time).

Air conditioning system

14 A pressure-operated switch and
compressor clutch solenoid are connected to
the ECU, to enable it to determine how the
system is operating. The ECU can increase
idle speed or switch off the system, as
necessary, so that normal vehicle operation
and driveability are not impaired. See Chap-
ter 3 for further details, but note that diagnosis
and repair should be left to a dealer service
department or air conditioning specialist.

Testing

ECU (Electronic Control Unit)

15 Do not attempt to “test” the ECU with any
kind of equipment. If it is thought to be faulty,
take the vehicle to a Ford dealer for the entire
electronic control system to be checked using
the proper diagnostic equipment. Only if all
other possibilities have been eliminated
should the ECU be considered at fault, and
replaced.

Air mass meter

16 Testing of this component is beyond the
scope of the DIY mechanic, and should be left
to a Ford dealer.

Crankshaft speed/position sensor

17 Unplug the electrical connector from the
sensor.
18 Using an ohmmeter, measure the
resistance between the sensor terminals.
Compare this reading to the one listed in the
Specifications Section at the beginning of this
Chapter. If the indicated resistance is not
within the specified range, renew the sensor.
19 Plug in the sensor’s electrical connector
on completion.

Camshaft position sensor

20 The procedure is as described in
paragraphs 17 to 19 above.

Coolant temperature sensor

21 Refer to Chapter 3, Section 6.

Inlet air temperature sensor

22 Unplug the electrical connector from the
sensor which is located either in the air
cleaner (carburettor engines) or in the CFi unit
or inlet manifold (fuel-injected engines).
23 Using an ohmmeter, measure the
resistance between the sensor terminals.
Depending on the temperature of the sensor
tip, the resistance measured will vary, but it
should be within the broad limits given in the
Specifications Section of this Chapter. If the
sensor’s temperature is varied - by placing it
in a freezer for a while, or by warming it gently
- its resistance should alter accordingly.
24 If the results obtained show the sensor to
be faulty, renew it.

Throttle position sensor

25 Remove the air cleaner assembly or
plenum chamber as necessary for access (see
Chapter 4) then unplug the sensor’s electrical
connector.

6•6 Emissions control systems

26 Using an ohmmeter, measure the
resistance between the unit’s terminals - first
between the centre terminal and one of the
outer two, then from the centre to the
remaining outer terminal. The resistance
should be within the limits given in the Specifi-
cations Section of this Chapter, and should
alter smoothly as the throttle valve is moved
from the fully-closed (idle speed) position to
fully open and back again.
27 If the resistance measured is significantly
different from the specified value, if there are
any breaks in continuity, or if the reading
fluctuates erratically as the throttle is
operated, the potentiometer is faulty, and
must be renewed.

Vehicle speed sensor

28 Testing of this component is beyond the
scope of the DIY mechanic, and should be left
to a Ford dealer.

Manifold absolute pressure (MAP)
sensor

29 Testing of this component is beyond the
scope of the DIY mechanic, and should be left
to a Ford dealer.

Power steering pressure switch

30 Unplug the electrical connector from the
sensor.
31 Using an ohmmeter, measure the
resistance between the switch terminals. With
the engine switched off, or idling with the
roadwheels in the straight-ahead position,
little or no resistance should be measured.
With the engine running and the steering on
full-lock, the pressure increase in the system
should open the switch contacts, so that
infinite resistance is now measured.
32 If the results obtained show the switch to
be faulty, renew it.

Oxygen sensor

33 Testing of this component can be done
only by attaching special diagnostic
equipment to the sensor wiring, and checking
that the voltage varies from low to high values
when the engine is running; do not attempt to
“test” any part of the system with anything
other than the correct test equipment. This is

beyond the scope of the DIY mechanic, and
should be left to a Ford dealer.

Removal and refitting

General

34 Before disconnecting any of these
components, always disconnect the battery
terminals, negative (earth) lead first - see
Section 1 of Chapter 5.

ECU (Electronic Control Unit)

Note: The ECU is fragile. Take care not to
drop it, or subject it to any other kind of
impact. Do not subject it to extremes of
temperature, or allow it to get wet.
35 Working inside the vehicle, remove the
side cowl kick panel from the front
passenger’s footwell to gain access to the
ECU (see illustration).
36 Release the ECU from its retaining
bracket (see illustration), then unscrew the
retaining bolt and remove the wiring multi-
plug.
37 Refitting is the reverse of the removal
procedure.

Air mass meter

38 Releasing its wire clip, unplug the meter’s
electrical connector (see illustration).
39 Release the clips and lift the air cleaner
cover, then release the two smaller clips and
detach the meter from the cover.
40 Slacken the clamp securing the meter to
the inlet hose, and withdraw the meter.
41 Refitting is the reverse of the removal
procedure. Ensure that the meter and air
cleaner cover are seated correctly and
securely fastened, so that there are no air
leaks.

Crankshaft speed/position sensor

42 Refer to Chapter 5.

Camshaft position sensor

43 Release the fuel feed and return hoses
from their clip.
44 Releasing its wire clip, unplug the
sensor’s electrical connector. Remove the
retaining screw, and withdraw the sensor from
the cylinder head; be prepared for slight oil
loss (see illustration).

45 Refitting is the reverse of the removal
procedure, noting the following points:
a)

Apply petroleum jelly or clean engine oil
to the sensor’s sealing O-ring.

b)

Locate the sensor fully in the cylinder
head, and wipe off any surplus lubricant
before securing it.

c)

Tighten the screw to the specified torque
wrench setting.

Coolant temperature sensor

46 Refer to Chapter 3, Section 6.

Inlet air temperature sensor

47 Remove the air cleaner assembly or air
inlet ducting as necessary (refer to Chapter 4)
to gain access to the sensor.
48 Releasing its clip, unplug the sensor’s
electrical connector, then unscrew the sensor
from the CFi unit, inlet manifold, or resonator,
as applicable.
49 Refitting is the reverse of the removal
procedure. Tighten the sensor to the specified
torque wrench setting; if it is overtightened, its
tapered thread may crack the resonator.

Throttle position sensor

50 Remove the air cleaner assembly, where
necessary, for access (see Chapter 4).
51 Releasing its wire clip, unplug the
potentiometer’s electrical connector. Remove
the retaining screws, and withdraw the unit

Emissions control systems 6•7

4.38 Disconnecting the air mass meter

electrical connector

4.36 Release the ECU from its retaining

bracket, then unscrew the retaining bolt

and remove the wiring multi-plug

4.35 ECU location behind the side cowl

kick panel in the passenger’s footwell

4.44 Camshaft position sensor location in

cylinder head with retaining screw

(arrowed) - cylinder head cover shown

removed for clarity

6

from the throttle housing (see illustration). Do
not force the sensor’s centre to rotate past its
normal operating sweep; the unit will be
seriously damaged.
52 Refitting is the reverse of the removal
procedure, noting the following points:
a)

Ensure that the potentiometer is correctly
orientated (see illustration), by locating
its centre on the D-shaped throttle shaft
(throttle closed), and aligning the
potentiometer body so that the bolts pass
easily into the throttle housing.

b)

Tighten the screws evenly and securely
(but do not overtighten them, or the
potentiometer body will be cracked).

Vehicle speed sensor

53 The sensor is mounted at the base of the
speedometer drive cable, and is removed with
the speedometer drive pinion. Refer to the
relevant Section of Chapter 7, Part A or B, as
applicable.

Manifold absolute pressure (MAP)
sensor

54 The sensor is located at the rear of the
engine compartment, on the right-hand side
(see illustration).
55 Disconnect the wiring multi-plug, and
detach the vacuum hose from the base of the
sensor.
56 Undo the two retaining screws, and
withdraw the sensor from its location.
57 Refitting is the reverse of the removal
procedure.

Power steering pressure switch

58 Releasing its clip, unplug the switch’s
electrical connector, then unscrew the switch
(see illustration). Place a wad of rag
underneath, to catch any spilt fluid. If a sealing
washer is fitted, renew it if it is worn or damaged.
59 Refitting is the reverse of the removal
procedure; tighten the switch securely, then
top-up the fluid reservoir (see Chapter 1) to
replace any fluid lost from the system, and
bleed out any trapped air (see Chapter 10).

Oxygen sensor

Note: The sensor is delicate, and will not work
if it is dropped or knocked, if its power supply
is disrupted, or if any cleaning materials are
used on it.
60 Release the sensor’s electrical connector
from its bracket on the engine/transmission
front mounting, and unplug it to disconnect
the sensor.
61 Raising and supporting the front of the
vehicle if required to remove the sensor from
underneath, unscrew the sensor from the
exhaust system front downpipe; collect the
sealing washer (where fitted).
62 On refitting, clean the sealing washer
(where fitted) and renew it if it is damaged or
worn. Apply a smear of anti-seize compound
to the sensor’s threads, to prevent them from
welding themselves to the downpipe in
service. Refit the sensor, tightening it to its
specified torque wrench setting; a slotted
socket will be required to do this. Reconnect
the wiring, and refit the connector plug.

5

Evaporative emissions
control (EVAP) system

2

General description

1 This system is fitted to minimise the escape
of unburned hydrocarbons into the
atmosphere. Fuel evaporative emissions
control systems are limited on vehicles
meeting 15.04 regulations; carburettor float
chambers are vented internally, whilst fuel
tanks vent to atmosphere through a combined
roll-over/anti-trickle-fill valve. On vehicles
meeting the more stringent emissions
regulations, the fuel tank filler cap is sealed,
and a charcoal canister is used to collect and
store petrol vapours generated in the tank
when the vehicle is parked. When the engine
is running, the vapours are cleared from the
canister (under the control of the ECU via the
canister-purge solenoid valve) into the inlet
tract, to be burned by the engine during
normal combustion.
2 To ensure that the engine runs correctly
when it is cold and/or idling, and to protect
the catalytic converter from the effects of an
over-rich mixture, the canister-purge solenoid
valve is not opened by the ECU until the
engine is fully warmed-up and running under
part-load; the solenoid valve is then switched
on and off, to allow the stored vapour to pass
into the inlet.

Checking

3 Poor idle, stalling and poor driveability can
be caused by an inoperative canister-purge
solenoid valve, a damaged canister, split or
cracked hoses, or hoses connected to the
wrong fittings. Check the fuel filler cap for a
damaged or deformed gasket.
4 Fuel loss or fuel odour can be caused by
liquid fuel leaking from fuel lines, a cracked or
damaged canister, an inoperative canister-
purge solenoid valve, or disconnected,
misrouted, kinked or damaged vapour or
control hoses.
5 Inspect each hose attached to the canister
for kinks, leaks and cracks along its entire
length. Repair or renew as necessary.
6 Inspect the canister. If it is cracked or
damaged, renew it. Look for fuel leaking from
the bottom of the canister. If fuel is leaking,
renew the canister, and check the hoses and
hose routing.
7 If the canister-purge solenoid valve is
thought to be faulty, unplug its electrical
connector and disconnect its vacuum hoses.
Connect a battery directly across the valve
terminals. Check that air can flow through the
valve passages when the solenoid is thus
energised, and that nothing can pass when
the solenoid is not energised. Alternatively,
connect an ohmmeter to measure the
resistance across the solenoid terminals, and
compare this reading to the one listed in the
Specifications Section at the beginning of this

6•8 Emissions control systems

4.58 Power steering pressure switch

location at right-hand rear of engine

4.54 Manifold absolute pressure (MAP)

sensor location and connections

A MAP sensor

C Retaining screw(s)

B Vacuum hose

D Wiring multi-plug

4.52 Align the throttle position sensor “D”

section on throttle shaft (arrowed) when

refitting

4.51 Throttle position sensor securing

screws (arrowed)

Chapter. Renew the solenoid valve if it is
faulty.
8 Further testing should be left to a dealer
service department.

Component renewal

Charcoal canister-purge solenoid
valve

9 The solenoid is located at the front right-
hand side of the engine compartment, near
the headlight unit, on HCS and CVH engines
(see illustration). On Zetec engines, the valve
is clipped to the bulkhead, behind the engine
on the right-hand side. Locate the solenoid,
then remove any components as necessary to
improve access.
10 Disconnect the battery negative (earth)
lead (refer to Chapter 5, Section 1), then
unplug the valve’s electrical connector. Unclip
the valve from its location, then disconnect its
vacuum hoses and withdraw it.
11 Refitting is the reverse of the removal
procedure.

Charcoal canister

12 Disconnect the battery negative (earth)
lead (refer to Chapter 5, Section 1).
13 The canister is located in the forward
section of the right-hand wheel arch (beneath
the coolant expansion reservoir). Access to
the top of the unit is made by removing the
coolant expansion reservoir. Access to the
underside of the unit is gained by raising the
vehicle at the front and removing the
roadwheel on the right-hand side. Ensure that
the vehicle is securely supported on axle
stands before working under the wheel arch.
14 Disconnect the hose from the unit, and
plug it to prevent the ingress of dirt.
15 Undo the retaining screws, and withdraw
the unit from under the wheel arch.
16 Refit in the reverse order of removal.
Unplug the hose before reconnecting it, and
ensure that it is clean and securely
connected.

6

Pulse-air system - general
information, checking and
component renewal

2

General information

1 This system consists of the pulse-air
solenoid valve (fuel-injected models), the
pulse-air valve itself, the delivery tubing, a
pulse-air filter, and on some models, a check
valve. The system injects filtered air directly
into the exhaust ports, using the pressure
variations in the exhaust gases to draw air
through from the filter housing; air will flow
into the exhaust only when its pressure is
below atmospheric. The pulse-air valve can
allow gases to flow only one way, so there is
no risk of hot exhaust gases flowing back into
the filter.
2 The system’s primary function is raise
exhaust gas temperatures on start-up, thus
reducing the amount of time taken for the
catalytic converter to reach operating
temperature. Until this happens, the system
reduces emissions of unburned hydrocarbon
particles (HC) and carbon monoxide (CO) by
ensuring that a considerable proportion of
these substances remaining in the exhaust
gases after combustion are burned up, either
in the manifold itself or in the catalytic
converter.
3 To ensure that the system does not upset
the smooth running of the engine under
normal driving conditions, it is linked by the
pulse-air solenoid valve to the ECU on fuel-
injected models, so that it only functions
during engine warm-up, when the oxygen
sensor is not influencing the fuel/air mixture
ratio. On carburettor models, a temperature-
sensitive ported vacuum switch shuts the
system off when normal engine operating
temperature is reached.

Checking

4 Poor idle, stalling, backfiring and poor
driveability can be caused by a fault in the
pulse-air system.
5 Inspect the vacuum pipe/hose for kinks,

leaks and cracks along its entire length.
Repair or renew as necessary.
6 Inspect the filter housing and piping. If
either is cracked or damaged, renew it.
7 If the pulse-air solenoid valve is thought to
be faulty, unplug its electrical connector and
disconnect its vacuum hoses. Connect a
battery directly across the valve terminals,
and check that air can flow through the valve
passages when the solenoid is thus
energised, and that nothing can pass when
the solenoid is not energised. Alternatively,
connect an ohmmeter to measure the
resistance across the valve terminals, and
compare this reading to the one listed in the
Specifications at the beginning of this
Chapter. Renew the solenoid valve if it is
faulty.
8 Further testing should be left to a dealer
service department.

Component renewal

Pulse-air filter and housing (CVH
engines)

9 Detach the lid from the filter body, and lift
out the filter element from the housing (see
illustration). If required, the housing can be
removed by detaching the air hoses from the
base of the unit and withdrawing the unit from
the vehicle.
10 Refit in the reverse order of removal.

Pulse-air valve (CVH engines)

11 Disconnect the battery negative (earth)
lead (refer to Chapter 5, Section 1).
12 Detach the vacuum hoses from the valve
(see illustration).
13 Loosen off the air hose clamp, and detach
the air hose from the valve.
14 Detach the remaining air hose. Note the
orientation of the valve, and remove it from
the vehicle.
15 When refitting the valve, ensure that it is
fitted the correct way round. Refitting is
otherwise a reversal of removal the removal
procedure.

Emissions control systems 6•9

5.9 Charcoal canister-purge solenoid

valve and associated components located

at the front right-hand side of the engine

compartment near the headlight unit on

HCS and CVH engines

A Charcoal canister
B Purge solenoid valve
C Canister retaining bolt
D Canister vapour hose

6.9 Pulse-air system filter components on

CVH engines

A Filter housing lid B Filter element

6.12 Pulse-air valve and connections on

CVH engines

A Pulse-air valve
B Pulse-air filter housing
C Vacuum hose
D Air hose securing clamp

6