Fuel and Emissions System Description - VTEC System

Fuel and Emissions System Description - VTEC System

VTEC

- This system improves fuel efficiency and reduces exhaust emissions at all levels of engine speed, vehicle speed, and engine load.
- The VTEC system changes the cam profile to correspond to engine speed. It maximizes torque at low engine speed and output at high engine speed.
- The low lift cam is used at low engine speeds, and the high lift cam is used at high engine speeds.
- The rocker arm oil control solenoid switches both intake rocker arms of the VTEC system on and off; the solenoid is controlled by the ECM/PCM.
- The rocker arm oil pressure switch detects VTEC system oil pressure and sends this information to the ECM/PCM.










Operation

At low engine speed

At low engine speed, the rocker arm oil control solenoid is turned off by the ECM/PCM. Oil pressure from the rocker arm oil control valve does not enter the intake rocker shaft. Both intake rocker arms are lifted by the low lift cam lobe.






At high engine speed

At high engine speed, the rocker arm oil control solenoid is turned on by the ECM/PCM. Oil pressure from the rocker arm oil control solenoid enters into the intake secondary rocker arm via the intake rocker shaft, and it moves the VTEC switching piston in the rocker arm.

This causes the VTEC switching piston to slide into the intake primary rocker arm, locking the intake primary and secondary rocker arms together. Both intake rocker arms are lifted by the high lift cam lobe.