Operation CHARM: Car repair manuals for everyone.
Manuals through 2025 now available!

Our trusted friends have launched a new website named LEMON, which has newer manuals. It also contains all the CHARM manuals.

LEMON is the spiritual successor to CHARM, I recommend you try it!

Link: lemon-manuals.la or lemon-manuals.org.ua

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Frequency Valve: Description and Operation


The frequency valve is located behind the air filter. It is connected to the fuel distributor and the fuel tank return line. The frequency valve responds to varying signals from the ECU and operates to control the amount of fuel injected into each cylinder.