Variable Intake System (VIS)
The VIS changes the length of the inlet manifold using two ECM controlled actuators which move flaps to control the air flow. The actuators operate singularly or together to adjust the length of the inlet tract.
Using an 'H' bridge, the intake and plenum actuator's internal electronics changes the actuator motor's polarity and therefore the flap position. At each flap position change, the DC actuator motor is powered for approximately 0.5 seconds. The worm gear design ensures that the flap remains in the desired position, even when the electric motors are not powered.
Intake Tract Variable Manifold
The ECM controls the position of the flaps by modulating the relevant actuator's control signal. If the signal shifts from low (approximately 1 volt) to high (approximately 10 volts) the internal electronics interpret it as the flap must close. If the signal shifts from high to low, the flap must open.
At engine speeds of less than 3800 rpm both the intake and plenum flaps are closed. At engine speeds of approximately 3800 rpm and higher the intake flap begins to open, effectively shortening the length of the intake manifold. At engine speeds of 4800 rpm or higher both the intake and plenum flaps are open, providing the shortest length of intake manifold.
| Engine Speed | Intake Tract Flap | Plenum Intake Flap | Effect |
|---|---|---|---|
| Less than 3800 rpm | Closed | Closed | Long tracts |
| 3800 to 4800 rpm | Open | Closed | Short tracts |
| More than 4800 rpm | Open | Open | Open plenum |
Plenum Variable Intake Manifold
The ECM diagnoses via the actuator if the flap has assumed the correct position. It does this, by comparing the desired air flow with the actual air flow. A fault code is stored if the deviations are outside the tolerances. The codes can be read using a Land Rover approved diagnostic system.
If an actuator fails and the flap is in the open position, it is not possible to remove the actuator and flap assembly from the inlet manifold. A small indentation on the body of the actuator allows for a 3 mm Allen key to be pushed through the thin membrane wall of the actuator housing. The Allen key can be engaged in the spindle of the actuator motor which allows the flap to be turned to the closed position and consequently the actuator and flap assembly can then be removed from the intake manifold.