1998 JAGUAR X308 sensor

Intake Air Distribution and Filtering - Intake Air Distribution and Filtering
Description an
d Operation
I

ntake Air Distribution and Filtering - Normally Aspirated Vehicles
Air Intake Asse
mbly

The air cleaner assembly consists of a two piece box containing the air filter, an airflow/temperature unit and the air intake
duct which connects to the top of the throttle assembly. The en gine full load breather feeds into the intake duct from the
bank 1 camshaft cover. A tuned stub on the ai r intake duct reduces the intake noise level.
Mass Air Flow and Temperature Sensors

The intake air is monitored by the Mass Air Flow (MAF) sensor assembly which is fitted at the outlet of the air filter
assembly. Two sensors are incorporated in the MAF sensor assembly, measuring air flow and temperature (temperature
sensor arrowed); both sensors provide anal ogue signal inputs to the engine control module (ECM) and are further described
in Section 303-14.

P
arts List
CAUTION: Do not attempt to renew or adjust the throttle cable without consulting the relevant procedure. Two
procedures apply: reconnection of an original cable (19.70.04) or the fitting of a new cable (19.20.06).
The filtered air from the intake duct is drawn downwards through the throttle body to the intake elbow on which the throttle
body is mounted. The airflow through the throttle body is vari ed by the electrically operated throttle valve according to
driver demand and engine mana gement system requirements.
The throttle body assembly has the following features:
Con
vential cable operated input shaft connected to the accelerator pedal.
M

echanical guard to limit throttle angl
e should driver demand exceed ECM co ntrolled parameters and a mechanical
back-up in the event of a throttle motor failure.
Vacuum actuator for operation of the mech anical guard in cru
ise control mode.
Thr

ottle valve (blade) to regula
te air flow into the engine.
Thermostatic air valve to allow and con
t
rol air by-pass around the throttle.
D
C electric motor to operate the thro
ttle in response to ECM control.
Three
sensors (accelerator pedal, mechan
ical guard and the throttle valve) to relay positional information about the
input shaft to the ECM.
R
eturn and control springs fitted to th
e input shaft, mechanical guard, thro ttle valve and dc motor drive gear.
Throttle Cont
rol Modes
There are seven throttle control

modes:
1. 1. Normal
It
em
Par
t Number
De
scription
1—Acce

lerator pedal and mechanic
al guard position sensors
2—Throttl
e (blade)
position sensor
Throttle Body

2.2. Cruise
3. 3. Mechanica l
guard
4. 4. Fixed idle
5. 5. Redundancy
6. 6. Full authority
7. 7. Engine shut-down
Normal mode occurs when the EC M uses the mechanical and monitoring arrangem ent of the throttle valve to control throttle
opening. The ECM does not permit driver demand to be exceeded but it can be restricted to allow for such features as
stability / traction control, or engine power limitation.
The ECM determines engine idle speed by controlling the throttle valve motor to vary the blade angle between the non-
adjustable preset limits of the mechanic al guard and the throttle valve motor.
Cruise mode is engaged as a result of the ECM calculating and controlling the required throttle valve opening via the
vacuum system. When the driver releases the throttle pedal, the input shaft disengages from the mechanical guard or the
vacuum actuator pulls the guard away from th e throttle valve. The throttle pedal will feel light should it be pushed again to
accelerate (pressing the pedal further will re-engage the input shaft with the mechanical guard and restore normal feel).
The ECM utilizes sensors to monitor the relative positions of the mechanical guard and throttle valve and adjusts them to
maintain the set cruise speed.
Mechanical guard mode permits full mechanical operation of the throttle if the ECM detects that a problem has been
encountered with the throttle valve position sensor, dc motor, associated harnesses / connecto rs or the ECM.
Fixed idle mode occurs when any two of the three sensors (two input shaft sensors and the mechanical guard sensor) fail.
The ECM will assume values which represent a blade angl e of approximately 2,5° and 1200 rpm (unloaded) maximum
engine speed.
Redundancy mode occurs when any one of the three sensors (two input shaft sensors and the mechanical guard sensor)
fails. The operational pair will be deemed to be safe to co ntinue without intervention, but cruise will be inhibited.
Full authority mode is invoked when a mech anical guard failure occurs which indicates that the guard is stuck fully open.
The red warning lamp will be lit and road speed will be li mited to 120 kph.
Engine shut-down mode will occur followin g multiple failures, such as mechanical guard mode following full authority mode
(or vice versa) or the throttle blade sticks.
Intake Elbow

The intake elbow directs the metered airflow from the electronic throttle to the intake manifold. Stub pipes on both sides of

the
intake elbow provide connections for vacuum actuators and are also used to redirect emissions into the engine.
On the right-hand side of the elbow a la rge diameter pipe connects to the brake servo. The smaller pipe provides a vacuum
feed to the fuel rail pressure regulator and throttle cruise control system. On the le ft-hand side of the elbow the front pipe
supplies vacuum control for the evaporative emissions system valves.
Emissions from the engine part load breather (bank 2) and pu rged fuel vapor from the EVAP valve are drawn via a common
T piece into the left-hand side of the intake elbow. Re-cir culated exhaust gas enters the intake elbow via the EGR valve
which is mounted directly on the rear of the elbow : where the EGR system is not used, a blanking plate is fitted.
The fuel system, throttle and emission control system s are described more fully in the relevant sections.
Intake Manifold

Filtered air from the vehicle's intake ducting is metered by th e electronic throttle and distributed to the two cylinder banks
via an integral intake manifold.
The intake manifold is manufactured in plastic with integral plastic fuel rails and metal-thread inserts; the very smooth
internal surfaces give excellent air flow.
Individual ducts lead off a central chamber to the inlet valves of each cylinder.
Silicon-rubber gaskets, loca ted in channels in the intake manifold, seal th e joints between the ducts and the cylinder heads.
Engine Ventilation

The e
ngine is ventilated through two brea
thers; a part-load breather and a full-load breather, one on each camshaft cover.
The outlet hose for the part-load breather is connected between the bank 2 camshaft cover and the intake elbow. The full-
load outlet hose is connected from the bank 1 camshaft cover to the intake duct between the MAF sensor assembly and the
throttle body.
Constructed in plastic, the hoses incorporate O-ring seal s and quick-release connectors; refer to Section 303-01.
I
ntake Air Distribution and Filtering - Supercharged Vehicles
Ai
r is supplied to the supercharger via an
intake cleaner/duct, throttle assembly and intake elbow which are similar to those
used for normally aspirated engines. The su percharger delivers pressurized air to two separate charge air cooler units, each
unit being mounted on the cy linder bank which it supplies. Pr essurized cooled air is fed from the charge air coolers directly
into each inlet port.

The air cleaner assembl y
consists of a tw
o piece box containing the ai r filter, an airflow/temperature unit (MAF sensor) and
the air intake duct which connects to the top of the throttle assembly. The engine full load breather feeds into the intake
duct from the bank 1 camshaft cover. Two tuned stubs on the air intake duct reduce the intake noise level.
Temperature Sensor

A second intake air temperature sensor (IAT sensor 2) is fitted at the outlet of the bank 1 charge air cooler. The sensor
provides an input to the ECM.
Air Intake Asse mbly

P a
rts List
It
e
m
Par
t
Number
De
scr
iption
1—Inta
k
e Air Temperature Sensor 2
2—Charge Air Cooler - Bank 1
3—Charge Air Cooler - Bank 2
4—Charge Air Cooler - Inlet Duct
5—Supercharger
Outlet D
uct
6—Supercharger
7—Supercharger
Pull
ey
8—Supercharger
Dri
ve Belt

Intake Air Distribution and Filtering - Charge Air Cooler RH
Remo
val and Installation
Remov
a
l
Installation
1. Disc onne
ct battery ground cable (IMPORTANT, see SRO
86.15.19 for further information).
2. Drain radiator coolant; refer to 26.10.01.
3. Remove air cleaner cover / intake assembly; refer to 19.10.30.
4. Remove throttle body; refer to 19.70.04.
5. Remove exhaust gas re-circulation valve (EGR) if installed;
refer to 17.45.01.
6. Remove throttle intake elbo w; refer to (SC) 19.70.28.
7. Remove supercharger outlet duct; refer to 18.50.16.
8. Remove coolant outlet pipe; refe r to operation (SC) 26.31.08.
9. Remove supercharger drive belt; refer to 18.50.08.
10. Remove supercharger; refer to operation 18.50.15.
11. Remove intake air temperatur e sensor 2 from charge air
cooler; refer to 18.30.52.
12. Detach engine harness retaining clip from rear of charge air
cooler.

13. Di
sconnect hoses from charge air cooler.
Pla

ce absorbent cloth in appropriate position.
Di
sc
onnect hoses.

14 . CAUTI
ON: Take care to avoi
d dropping any objects or
foreign matter into engine inle t duct with charge air cooler
removed.
Remove charge air cooler from the engine. 1. Remove eight bolts.
Remove charge air cooler.
2
. Discard gasket.
Cle
a
n all mating faces.
1.
Install ch arge air
cooler to adaptor.
1. Install new gasket.
2. Install charge air cooler.

2.
Conne
ct hoses to charge air cooler.
Conne

ct hoses.
3. Install intake air te mperature sensor 2 to charge air cooler;
refer to 18.30.52.
4. Install supercharger; refer to 18.50.15.
5. Install supercharger driv e belt; refer to 18.50.08.
6. Install engine coolant outlet pipe; refer to 26.31.08.
7. Install supercharger outlet du ct and new gasket; refer to
18.50.16.
8. Install throttle intake elbow; refer to 19.70.28.
9. Install exhaust gas re-circulation valve (EGR) if applicable;
refer to 17.45.01.
10. Install throttle body; refer to 19.70.04.
11. Install air cleaner cover / intake assembly; re fer to 19.10.30.
12. Refill cooling system; refer to (SC) (26.10.01).
13. Reconnect battery ground cable (IMPORTANT, see SRO
86.15.15 for further information).