Subaru 2002 Impreza Service Manual page 57

AIR LINE
Fuel Injection (Fuel System)
G: TUMBLE GENERATOR VALVES
0
A tumble generator valve is provided on each engine bank, between the intake manifold and
intake air ports. The right bank tumble generator valve has butterfly valves for the #I and #3 cylin-
ders and the left bank tumble generator valve
has
those for the #2 and #4 cylinders. The two butter-
fly valves in each tumble generator valve are fitted on a single shaft that is driven by an actuator.
0
The tumble generator valves are controlled by the ECM according to the coolant temperature
and the time elapsed after start of the engine. When the engine is started, the butterfly valves are
moved to the closing ends. In this state, the intake air flows at very high speeds passing through
narrowed passages in the directions determined by the individual intake air ports in the cylinder
head. This creates tumbling air motions in the cylinders, which enables lean mixtures to be ignited
and thus harmful exhaust emissions to be reduced during engine start. The tumble generator
valves are fully open when the engine is operating at an ordinary driving speed, allowing intake
air to flow without being changed in direction and velocity.
\
NF0322
(A) Activated
(B) Not activated
(1) Actuator
(2) Tumble generator valve position sensor
(3)
Tumble generator housing
(4) Intake manifold
(5) Tumble generator valve
(6) Tumble generating air passage
(7) Intake main air passage
(8) Piston
(9) Injector
(1 0) Cylinder head
FU-7