1998 JAGUAR X308 vacuum

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 intake elbow di
rects the metered airflow from the electronic throttle outlet (und
erside of the throttle body) into the
intake of the supercharger.
The supercharger by-pass valve assembly is bolted to the intake elbow. The butterfly valve inside the assembly is opened
by a diaphragm actuator operated by vacu um feed from the elbow. At closed or partially open throttle positions, the
butterfly valve opens, allowing th e airflow from the two charge air cooler inlets to be directed back to the supercharger inlet .
This action inhibits the supercharging e ffect and reduces engine torque to non supercharged levels. Progressive opening of
the throttle causes the by-pass valve to gradually close.
On the right-hand side of the elbow a la rge diameter pipe connects to the brake servo. On the left-hand side the smaller
pipe supplies vacuum control for the evaporative emissions system valves.
Emissions from the engine part load breather (bank 1) 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 and emission control systems are described more fully in the relevant sections.
Fuel Pressure Regula
tion and
Cruise Control Vacuum Feed
The inlet v
acuum feed fo
r the fuel rail pressure regula tor and the cruise control system is taken from the supercharger
outlet duct. The feed pipe is located below the large charge air cooler coolant filler plug.
Superchar
ger
and associated components
Inta
ke Elbow and Bypass

2. Fi
t the two bolts which secure the intake tube to the
throttle body.
4. Reconnect the air flow meter multi-plug.
5. Fit a new strap to secures the vacuum pipe to the induction
elbow.

6. Connect the breather pipe to
the A-bank camshaft cover.
1. Fit a new O-ring seal to the breather pipe.
2. Reconnect the breather pipe to the stub pipe.

Intake Air Distribution and Filtering - Supercharger Outlet Pipe
Remo
val and Installation
Remov
a
l
1.
Re
move air cleaner cover / intake
assembly; refer to 19.10.30.
2. Drain radiator coolant; refer to operation (SC) 26.10.01.

3. Disc
onnect coolant hoses and vacuum pipe from supercharger
outlet duct.
Pl a
ce absorbent rags under
the two coolant hoses which
are connected to the outlet duct.
1. Remove vacuum pipe.
2. Disconnect hoses.
Plu g
hoses and outlet duct stub pipes to prevent spillage.

4. CAUTIO
N: Take care to avoi
d any coolant from dripping
into supercharger.
Remove supercharger outlet duct. 1. Remove three bolts.
2. Remove four bolts.
Di
scard rubber seals from bolts.
3. Remove outlet duct.
Discard ou
tlet duct gasket.
5.
Bla
nk supercharger outlet with
body tape, or similar, to
prevent ingress of foreign matter.

6. Remove charge air c oo
ler inlet assembly.
1. Remove two bolts.
2. Remove two bolts.
3. Remove charge air cooler inlet assembly.
7. Remove ducts from charge air cooler inlet assembly.
1. Remove two clamp plates.
2. Discard two ducts.

4. Secure charge air cool
er inlet as
sembly to supercharger outlet
duct.
1. Install bolts.

5. Inst al
l coolant hoses and vacuum pipe to outlet duct.
1. Install vacuum pipe.
2. Install coolant hoses.
6. Refill cooling system; refer to (SC) (26.10.01).
7. Install intake tube / air fl ow meter / air cleaner cover
assembly; refer to 19.10.30.

Intake Air Distribution and Filtering - Thrott
le Body Elbow
Re
mo
val and Installation
Remov
a
l
1.
WARNING: B E
FORE PROCEEDING, IT IS ESSENTIAL THAT

WARNING NOTES GIVEN IN SECTION 100-00 (UNDER HEADING
'SAFETY PRECAUTIONS') AR E READ AND UNDERSTOOD.
Disconnect battery ground cable (IMPORTANT, see SRO
86.15.19 for further information).
2. Re
move air cleaner cover / inta
ke assembly; refer 19.10.30.
3. Remove throttle assemb ly; refer to 19.70.04.
4. Remove exhaust gas recirculation (EGR) valve where installed;
refer 17.45.01.

5. Re
lease intake elbow from right-hand support bracket.
Re
lea
se brake servo vacuum pi
pe and disconnect pipe.
1. Disconnect vacuum pipe.
2. Remove upper bolt.

6. Relea
se intake elbow from le
ft-hand support bracket.
1. Disconnect vacuum pipe.
2. Disconnect engine breather T-piece.
3. Remove upper bolt.
4. Loosen, but do not remove, lower two bolts.

7. Re
move intake elbow from supercharger.
1. Release and pull back cl ips securing bypass hoses
at charge air coolers.
2. Remove four bolts.
3. Remove hoses from charge air cooler stub pipes.
Re move as
sembly from vehicle.
4. Discard gasket.
Cle a
n all mating faces.
8. Remove by-pass valve assembly from intake elbow.

2.
Fully tighten two bolts.
3. Connect breather/purge pipe T-piece to intake elbow.
4. Connect vacuum pipe to intake elbow.

5. Install right-hand support brac
ket to intake elbow.
1. Install bolt.
6. Install exhaust gas re-circulation valve (EGR) if applicable;
refer to 17.45.01.
7. Install throttle assemb ly; refer to 19.70.04.
8. Install air cleaner cover / intake assembly; refer to 19.10.30.
9. Reconnect battery ground cable (IMPORTANT, see SRO
86.15.15 for further information).