Carburetor pneumatic valve control system (VAZ-2105)

The system is used to turn off and on the carburetor pneumatic valve (shut-off of vacuum supply to the forced idle economizer) at forced idle. The main unit of the system is the electronic control unit (Fig. 251) type 25.3761. It switches off the pneumatic valve 4 when the engine crankshaft speed increases above 1600 min⁻¹ and switches on the pneumatic valve when the speed decreases below 1200 min⁻¹. Control pulses (proportional to crankshaft speed) are supplied to the unit from the end of the primary winding of the ignition coil.



The control unit can switch off the pneumatic valve only if the contacts of the microswitch 3 of the carburetor are open, i.e. if the carburetor throttle control pedal is not pressed. If you press the pedal, the pneumatic valve will not switch off or will switch on if it was switched off.

Before checking the control unit, make sure that the wires are connected to it correctly. Check the unit's functionality using a voltmeter (with a measurement range of 0-15 V) in the following order.

Disconnect the wires from the microswitch installed on the carburetor. Connect voltmeter 2 (Fig. 252) to the control unit using a special adapter connector. Start the engine and, gradually increasing the rotation speed, monitor the voltmeter readings: after starting the engine, it should show a voltage of at least 10 V, and at the moment the pneumatic valve is disconnected, a sudden decrease in voltage to a value of no more than 1.5 V. After disconnecting the pneumatic valve, gradually reduce the rotation speed until the pneumatic valve is connected. In this case, the voltmeter should show a sudden increase in voltage of at least 10 V.





It is permissible to check the functionality of the control unit without a voltmeter and adapter connector by the characteristic sound of the valve when turned off and on.

[The original is posted on Internet resource: VAZbook.ru]