Pickup & 4Runner Models

During 4WD operation it is necessary to enrichen the fuel mixture to compensate for engine load. This is accomplished by the use of a 4WD indicator switch, the ECU and a vacuum switching valve.

When the vehicle is shifted into 4WD mode, the 4WD indicator switch is closed, sending a signal to the ECU. The ECU then signals the vacuum switching valve to cut off the vacuum signal to the fuel pressure regulator. This action increases the amount of fuel available to the fuel injectors.