fuel tank removal FORD SIERRA 1982 1.G Fuel And Exhaust Systems Fuel Injection Workshop Manual

General
Fuel tank capacity (all models) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60.0 litres (13.1 gallons)
Fuel octane rating:
Leaded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 RON (4-star)
Unleaded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 RON (Premium)
*Models fitted with a catalytic converter must be operated on unleaded fuel at all times. Do not use leaded fuel in such models, as the catalyst will
be destroyed:
System control pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5 bar
System type:
2.0 litre SOHC models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bosch L-Jetronic
2.0 litre DOHC models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multi-point fuel injection system, controlled by EEC IV engine
management system
1.6 and 1.8 litre (R6A type) CVH models . . . . . . . . . . . . . . . . . . . . . . . . Central fuel injection (CFI) controlled by EEC IV engine management
system
Idle adjustments
All models except 2.0 litre DOHC
Idle speed (dependent on idle speed adjustment wire):
Manual gearbox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875 rpm
Automatic transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 rpm
Idle mixture (CO content) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5 to 1.0%
2.0 litre DOHC
Idle speed (not adjustable) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 875 + 50 rpm
Idle mixture (CO content) - models without catalytic converter . . . . . . . 1.0 to 1.5%
Chapter 4 Part B:
Fuel and exhaust systems - fuel injection
Air cleaner element - renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Air cleaner - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Airflow meter - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . .15
Carbon canister (models with catalytic converter) - removal and
refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Carbon canister-purge solenoid (models with catalytic converter) -
removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
CFI unit (1.6 and 1.8 litre (R6A type) CVH) - removal and refitting . . .19
Electronic vacuum regulator (1.8 litre (R6A type) CVH) - removal and
refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
Exhaust gas oxygen (HEGO) sensor (2.0 litre DOHC/1.6 & 1.8 litre
(R6A type) CVH) - removal and refitting . . . . . . . . . . . . . . . . . . . . .35
Exhaust gas recirculation valve (1.8 litre (R6A type) CVH) - removal
and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
Exhaust manifold - removal and refitting . . . . . . . . . . . . . . . . . . . . . .36
Exhaust pressure transducer (1.8 litre (R6A type) CVH) - removal and
refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
Exhaust system - inspection, removal and refitting . . . . . . . . . . . . . .37
Fuel filter - renewal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
Fuel injector ballast resistor (1.6 litre CVH) - removal and refitting . .17
Fuel injector (1.6 and 1.8 litre (R6A type) CVH) - removal and
refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Fuel injectors - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . .18
Fuel level sender unit (2.0 litre SOHC) - removal and refitting . . . . . .11Fuel pressure regulator - removal and refitting . . . . . . . . . . . . . . . . . .6
Fuel pump/fuel level sender unit (2.0 litre DOHC/1.6 & 1.8 litre (R6A
type) CVH) - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . .9
Fuel pump (2.0 litre SOHC) - removal and refitting . . . . . . . . . . . . . . .8
Fuel pump - testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7
Fuel system (1.6 and 1.8 litre (R6A type) CVH) - depressurisation . . . .4
Fuel tank - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
General information and precautions . . . . . . . . . . . . . . . . . . . . . . . . . .1
Idle speed and mixture - adjustment . . . . . . . . . . . . . . . . . . . . . . . . .12
Idle speed control valve - removal and refitting . . . . . . . . . . . . . . . . .13
Inlet manifold - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . .30
Mixture adjustment potentiometer (2.0 litre DOHC) - removal and
refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Pulse-air control solenoid (1.6 litre CVH) - removal and refitting . . . .23
Pulse-air delivery tubing (1.6 litre CVH) - removal and refitting . . . . .22
Pulse-air filter element (1.6 litre CVH) - renewal . . . . . . . . . . . . . . . . .20
Pulse-air system vacuum-operated air valve (1.6 litre CVH) - removal
and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Throttle body - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . .29
Throttle cable - removal, refitting and adjustment . . . . . . . . . . . . . . .26
Throttle pedal - removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . .25
Throttle position sensor - removal and refitting . . . . . . . . . . . . . . . . .27
Throttle valve control motor (1.6 and 1.8 litre (R6A type) CVH) -
removal and refitting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
4B•1
Specifications Contents
4B
Easy,suitable for
novice with little
experienceFairly easy,suitable
for beginner with
some experienceFairly difficult,
suitable for competent
DIY mechanic
Difficult,suitable for
experienced DIY
mechanicVery difficult,
suitable for expert
DIY or professional
Degrees of difficulty

manual mixture adjustment is possible.
On models with a catalytic converter, an
evaporative emission control (EVAP) system is
fitted. This prevents the release of fuel vapour
into the atmosphere. With the ignition
switched off, vapours from the fuel tank are
fed to a carbon canister, where they are
absorbed. When the engine is started, the
EEC IV module opens a purge solenoid valve,
and the fuel vapours are fed into the inlet
manifold and mixed with fresh air. This cleans
the carbon filter. A blow-back valve prevents
inlet air being forced back into the fuel tank.
A fuel pump inertia switch is fitted. This
switch breaks the electrical circuit to the fuel
pump in the event of an accident or similar
impact, cutting off the fuel supply to the engine.
A “limited operation strategy” (LOS) means
that the vehicle will still be driveable, albeit at
reduced power and efficiency, in the event of
a failure in the EEC IV module or its sensors.
1.6 and 1.8 litre (R6A type) CVH models
The fuel injection system fitted to these
models is under the overall control of an EEC
IV engine management system which also
controls the ignition timing.
Fuel is supplied from the rear-mounted fuel
tank by an electric fuel pump which is integral
with the fuel level sender unit mounted inside
the fuel tank. Fuel passes via a fuel filter to the
Central Fuel Injection (CFI) unit. A fuel
pressure regulator, mounted on the CFI unit,
maintains a constant fuel pressure to the fuel
injector. Excess fuel is returned from the
regulator to the tank.
The CFI unit, resembling a carburettor,
houses the throttle valve, throttle valve control
motor, throttle position sensor, air charge
temperature sensor, fuel injector, and
pressure regulator.
The duration of the electrical pulse supplied
to the fuel injector determines the quantity of
fuel injected, and pulse duration is computed
by the EEC IV module on the basis of
information received from the various sensors.
The fuel injector receives a pulse twice per
crankshaft revolution under normal operating
conditions, and once per crankshaft
revolution under engine idle conditions. A
ballast resistor is used in the fuel injector
control circuit on 1.6 litre engines.
Inlet air passes through the air cleaner into
the CFI unit. The volume of air entering the
engine is calculated by the EEC IV module from
information supplied by various sensors. These
sensors include the air charge temperature
sensor and throttle position sensor, mounted in
the CFI unit; a crankshaft speed/position
sensor which supplies information on engine
speed; and a manifold absolute pressure (MAP)
sensor which measures the pressure of the air
entering the engine.
Additional sensors inform the EEC IV module
of engine coolant temperature, and vehicle
speed (from a gearbox-mounted sensor).
An exhaust gas oxygen (HEGO) sensor
enables the EEC IV module to control the
fuel/air mixture to suit the operating
parameters of the catalytic converter. No
manual mixture adjustment is possible.
Idle speed is controlled by a throttle valvecontrol motor, which controls the position of
the throttle valve under conditions of idling,
deceleration/part-throttle, and engine start-up
and shut-down.
On 1.6 litre engines, a pulse-air system is
fitted to reduce the exhaust gas emissions
during engine warm-up. The system is con-
trolled by a vacuum-operated valve, which is
operated by the EEC IV module via a solenoid.
The system introduces air into the exhaust
manifold to increase the exhaust gas
temperature, which oxidises more of the
pollutants, and brings the catalyst up to
working temperature more quickly. The
system operates until the catalyst reaches
operating temperature, when the control
solenoid shuts off the system.
On 1.8 litre engines, an exhaust gas
recirculation (EGR) system is used to
recirculate a small amount of exhaust gas into
the inlet manifold. This process lowers the
combustion temperature, resulting in a
reduction of NOx (oxides of nitrogen)
emissions. The EGR system is controlled by
the EEC IV module in conjunction with an
Electronic Pressure Transducer (EPT) and an
Electronic Vacuum Regulator (EVR).
On certain models, an evaporative emission
control system may be fitted. This prevents
the release of fuel vapour into the
atmosphere. With the ignition switched off,
vapours from the fuel tank are fed to a carbon
canister, where they are absorbed. When the
engine is started the EEC IV module opens a
purge solenoid valve, and the fuel vapours are
fed into the inlet manifold and mixed with
fresh air. This cleans the carbon filter. A blow-
back valve prevents inlet air being forced
back into the fuel tank.
A fuel pump inertia switch is fitted. This
switch breaks the electrical circuit to the fuel
pump in the event of an accident or similar
impact cutting off the fuel supply to the engine.
A “limited operation strategy” (LOS) means
that the vehicle will still be driveable, albeit at
reduced power and efficiency, in the event of
a failure in the EEC IV module or its sensors.
Precautions
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.
Residual pressure will remain in the fuel
lines long after the vehicle was last used,
therefore extra care must be taken when
disconnecting a fuel line hose. Loosen any
fuel hose slowly to avoid a sudden release of
pressure which may cause fuel spray. As an
added precaution place a rag over each union
as it is disconnected to catch any fuel which is
forcibly expelled.
Certain adjustment points in the fuel system
(and elsewhere) are protected by
“tamperproof” caps, plugs or seals. The
purpose of such tamperproofing is todiscourage, and to detent, adjustment by
unqualified operators.
In some EEC countries (though not yet in
the UK) it is an offence to drive a vehicle with
missing or broken tamperproof seals. Before
disturbing a tamperproof seal, satisfy yourself
that you will not be breaking local or national
anti-pollution regulations by doing so. Fit a
new seal when adjustment is complete when
this is required by law.
Do not break tamperproof seals on a
vehicle which is still under warranty.
Catalytic converter - precautions
The catalytic converter is a reliable and simple
device which needs no maintenance in itself,
but there are some facts of which an owner
should be aware if the converter is to function
properly for the full service life.
a)DO NOT use leaded petrol in a car
equipped with a catalytic converter the
lead will coat the precious metals,
reducing their converting efficiency and
will eventually destroy the converter.
b)Always keep the ignition and fuel systems
well-maintained in accordance with the
manufacturers schedule, ensure that the
air cleaner filter element, the fuel filter
(where fitted) and the spark plugs are
renewed at the correct interval if the inlet
air/fuel mixture is allowed to become too
rich due to neglect, the unburned surplus
will enter and burn in thecatalytic
converter, overheating the element and
eventually destroying the converter.
c)If the engine develops a misfire, do not
drive the car at all (or at least as little as
possible) until the fault is cured - the
misfire will allow unburned fuel to enter
the converter, which will result in
overheating, as noted above.
d)DO NOT push- or tow-start the car - this
will soak the catalytic converter in
unburned fuel, causing it to overheat when
the engine does start - see b) above.
e)DO NOT switch off the ignition at high
engine speeds - if the ignition is switched
off at anything above idle speed,
unburned fuel will enter the (very hot)
catalytic converter, with the possible risk
of igniting on the element and damaging
the converter.
f)DO NOT use fuel or engine oil additives -
these may contain substances harmful to
the catalytic converter.
g)DO NOT continue to use the car if the
engine burns oil to the extent of leaving a
visible trail of blue smoke - the unburned
carbon deposits will clog the converter
passages and reduce the efficiency; in
severe cases the element will overheat.
h)Remember that the catalytic converter
operates at very high temperatures - hence
the heat shields on the car’s underbody
and the casing will become hot enough to
ignite combustible materials which brush
against it - DO NOT, therefore, park the car
in dry undergrowth, over long grass or
piles of dead leaves.
i)Remember that the catalytic converter is
FRAGILE, do not strike it with tools during
servicing work, take great care when
Fuel and exhaust systems - fuel injection 4B•3
4B

21Fit the small spring, valve, diaphragm
(ensuring that it locates correctly), large
spring, and the spring cup.
22Carefully place the ball into position on
the spring cup, and ensure that it locates
correctly.
23Refit the regulator housing, taking great
care to avoid disturbing the ball, and once
correctly in position, tighten the screws evenly
to avoid distorting the diaphragm.
24Refit the CFI unit.
25On completion, the fuel system pressure
should be checked by a Ford dealer at the
earliest opportunity.
1.8 litre
26Disconnect the battery negative lead.
27Remove the air cleaner assembly.
28Depressurise the fuel system and
disconnect the fuel inlet pipe from the CFI unit
(see illustration).
29Disconnect the fuel injector/regulator
wiring plug, and move the wiring harness
clear.
30Undo the four screws, and carefully lift the
injector/regulator assembly off the CFI unit.31Refitting is a reversal of removal. On
completion, the fuel system pressure should
be checked by a Ford dealer at the earliest
opportunity.
1If the fuel pump is functioning, it should be
possible to hear it “buzzing” by listening
under the rear of the vehicle when the ignition
is switched on. Unless the engine is started,
the fuel pump should switch off after
approximately one second. If the noise
produced is excessive, this may be due to a
faulty fuel flow damper (not fitted to 2.0 litre
DOHC models). The damper can be renewed
by unscrewing it from the pump outlet union.
2If the pump appears to have failed
completely, check the appropriate fuse and
relay, and where applicable check the state of
the fuel pump inertia cut-off switch as follows.
3The inertia cut-off switch is fitted to all
models from mid-1986 onwards, and can be
found behind the passenger compartment
left-hand side trim panel on Hatchback and
Estate models up to the 1987 model year (see
illustration). The location of the switch for all
other models is in the spare wheel well (see
illustration). The switch incorporates a reset
button, which should normally be in the
depressed position. Check the position of the
reset button before assuming that a fault
exists in the fuel pump.
4To test the fuel pump, special equipment is
required, and it is recommended that any
suspected faults are referred to a Ford dealer.
Removal
1The fuel pump is located under the rear of
the vehicle next to the fuel tank (see
illustration).
2Disconnect the battery negative lead.
3Chock the front wheels, then jack up the
rear of the vehicle and support on axle stands
(see “Jacking and Vehicle Support”).
4Clean the area around the pump mounting,
and position a suitable container under the
pump.
5Using a hose clamping tool or self-locking
pliers, clamp the fuel tank-to-pump hose to
prevent excessive petrol spillage, or
8Fuel pump (2.0 litre SOHC) -
removal and refitting
7Fuel pump - testing
4B•6Fuel and exhaust systems - fuel injection
7.3a Fuel pump inertia cut-off switch - pre-
1987 SOHC Hatchback and Estate models
A Activated mode (fuel cut-off)
B Normal mode (fuel flowing)
C Trim panel access hole
8.1 Fuel pump location
A Inlet hose
B Outlet hoseC Electrical feed
D Flow damper7.3b Fuel pump inertia cut-off switch
location (arrowed) under spare wheel
6.28 Fuel injector/pressure regulator attachments - 1.8 litre (R6A) CVH
A Pressure regulator assembly
B Fuel inlet pipeC Injector/regulator wiring plug
D Injector/regulator screws
Caution: Refer to the
precautions in Section 1 before
proceeding.

alternatively make arrangements to collect the
contents of the fuel tank which will otherwise
be released. Disconnect the hose from the
pump.
6Slowly loosen the fuel flow damper fitted to
the pump outlet union, to relieve the pressure
in the fuel line, then remove the damper and
disconnect the outlet pipe from the pump.
Plug the end of the pipe to prevent excessive
petrol spillage.
7Disconnect the wiring plug(s), then slacken
the clamp bolt and slide the pump from the
bracket assembly.
Refitting
8Refitting is a reversal of removal, noting the
following.
9When refitting the flow damper to the pump
ensure that the pump outlet pipe is correctly
routed (see illustration). It is possible to
inadvertently rotate the banjo union through
180º, which routes the outlet pipe too close to
the exhaust.
10After refitting and securing the pump, but
before lowering the vehicle, reconnect the
battery and switch the ignition on and off
several times to pressurise the fuel system.
Check for leaks around the pump; if all is
satisfactory, switch off the ignition and lower
the vehicle.1Remove the fuel tank.
2Unscrew the fuel pump/fuel level sender
unit by engaging two crossed screwdrivers in
the slots on either side of the unit mounting
flange. Recover the seal.
3Refitting is a reversal of removal but fit a
new seal.
Refer to Chapter 4 Part A, Section 9.
Refer to Chapter 4 Part A, Section 10.
Refer to Chapter 1, Sections 15 and 16.
Note: A new gasket must be used when
refitting the valve.
2.0 litre SOHC models
1Disconnect the battery negative lead.
2Disconnect the idle speed control valve
wiring plug by releasing the retaining clip and
pulling on the plug, not the wiring (see
illustration).
3Unscrew the two retaining nuts and
withdraw the valve from the inlet manifold
(see illustration). Recover the gasket.4Clean the valve and manifold mating faces
before refitting, taking care not to allow dirt to
enter the manifold.
5Refitting is a reversal of removal, using a
new gasket.
6On completion, start the engine and check
that the idle speed is stable if not, check for
air leaks around the valve. Switch on all
available electrical loads and check that the
idle speed is maintained - if not, suspect a
faulty valve.
2.0 litre DOHC models
7Disconnect the battery negative lead.
8Loosen the securing clip, and disconnect
the air inlet hose from the throttle body.
9Unscrew the securing nut, and release the
air inlet tube from the bracket on the engine
compartment front panel.
10Disconnect the wiring plug from the idle
speed control valve.
11Release the air cleaner lid securing clips
then remove the air inlet tube, plenum
chamber, and air cleaner lid as an assembly,
disconnecting the breather hose from the air
inlet tube.
12Unscrew the two securing bolts, and
withdraw the valve from the air inlet tube.
Recover the gasket (see illustration).
13Clean the valve and air inlet tube mating
faces before refitting, taking care not to allow
dirt to enter the air inlet tube.
14Refitting is a reversal of removal, using a
new gasket.
15On completion, start the engine and
check that the idle speed is stable if not,
check for air leaks around the valve. Switch
on all available electrical loads, and check
that the idle speed is maintained - if not,
suspect a faulty valve.
1The potentiometer is located at the rear
right-hand side of the engine compartment,
behind the MAP sensor.
2Disconnect the battery negative lead.
3Remove the screw, then withdraw the
potentiometer and disconnect the wiring plug.
4Refitting is a reversal of removal.
14Mixture adjustment
potentiometer (2.0 litre
DOHC) - removal and refitting
13Idle speed control valve -
removal and refitting
12Idle speed and mixture -
adjustment
11Fuel level sender unit (2.0 litre
SOHC) - removal and refitting
10Fuel tank - removal and refitting
9Fuel pump/fuel level sender
unit (2.0 litre DOHC/1.6 & 1.8
litre (R6A type) CVH) - removal
and refitting
Fuel and exhaust systems - fuel injection 4B•7
4B
13.2 Disconnecting the idle speed control
valve wiring plug13.12 Withdrawing the idle speed control
valve and gasket13.3 Unscrewing an idle speed control
valve retaining nut
8.9 Correct and incorrect routing of fuel
pump outlet pipe
A Fuel pump
B Outlet pipe
C Exhaust pipeX = 30.0 mm (1.2 in)
Y = 100.0 mm (3.9 in)
Caution: Refer to the
precautions in Section 1 before
proceeding.

1The EGR valve is located on the right-hand
side of the engine, below the CFI unit.
2Disconnect the battery negative lead.
3Disconnect the vacuum hose connecting
the EGR valve to the electronic vacuum
regulator (see illustration).
4Undo the nut securing the metal tube to the
underside of the valve. Undo the two bolts,
and remove the valve from the engine.
5Refitting is a reversal of removal, but
loosely fit the metal tube securing nut to the
EGR valve before fitting the valve in position.
Tighten the nut securely on completion.1The EPT unit is located on the right-hand
side of the engine, behind the CFI unit (see
illustration).
2Disconnect the battery negative lead.
3Remove the air cleaner assembly.
4Disconnect the EPT wiring plug, and slip
the unit out of its mounting bracket.
5Detach the vacuum hose, and remove the
unit from the car.
6Refitting is a reversal of removal.2.0 litre DOHC models
1Where fitted, the carbon canister is located
on the right-hand side of the engine
compartment, underneath the coolant
expansion tank.
2Disconnect the battery negative lead.
3Pull the plastic pipe from the canister (the
connector is a push-fit in the canister) (see
illustration).
4Unscrew the securing bolt, and lift the
canister from its location.
5Refitting is a reversal of removal.
1.6 and 1.8 litre (R6A type) CVH
models
6The carbon canister (where fitted) is located
on the right-hand side of the engine
compartment.
7Proceed as detailed in paragraphs 2 to 5
inclusive.
2.0 litre DOHC models
1The purge solenoid is located next to the
carbon canister, on the right-hand side of the
engine compartment.
2Disconnect the battery negative lead.
3Disconnect the solenoid wiring plug halves
by releasing the locktabs and pulling on the
plug halves, not the wiring.
34Carbon canister-purge
solenoid (models with
catalytic converter) - removal
and refitting
33Carbon canister (models with
catalytic converter) - removal
and refitting32Exhaust pressure transducer
(1.8 litre (R6A type) CVH) -
removal and refitting31Exhaust gas recirculation
valve (1.8 litre (R6A type)
CVH) - removal and refitting
4B•14Fuel and exhaust systems - fuel injection
31.3 Exhaust gas recirculation valve attachments -
1.8 litre (R6A) CVH
A Metal tube-to-EGR valve
retaining nut
B Vacuum hoseC EGR valve retaining bolts
D EGR valve metal tube location32.1 Exhaust pressure transducer attachments -
1.8 litre (R6A) CVH
A Exhaust pressure transducerB Vacuum hose
33.3 Carbon canister and purge solenoid locations - DOHC
A Carbon canister
B Purge solenoidC Canister retaining bolt
D Pipe