Frequency Valve

Frequency valve operates at constant frequency (70 Hz) as soon as engine is running. When frequency valve is closed, fuel pressure to injectors is determined by spring in each pressure regulating valve. When frequency valve is open, fuel pressure decreases in lower half of fuel distributor, tension on spring is relieved, and more fuel is directed to cylinders. See Figure .

The ECU grounds connection for frequency valve in different length pulses according to oxygen sensor input signal. This will open and close frequency valve for regulation of fuel mixture. When engine is cold, ratio of valve open to valve closed is about 60/40.

After engine warms up, voltage produced by oxygen sensor determines amount of time frequency valve must be open or closed. This ratio can be read with special tester or with dwell meter. Dwell reading of 45 degrees indicates ratio of 50% open, 50% closed.