This valve prevents the "running-on" of the engine after the ignition is switched off when, due to the heat of the engine, a condition of compression ignition or dieselling is set up.

The method of achieving engine cut off is by applying a slight manifold vacuum to the float chamber of the carburettor when the ignition is switched off. This prevents fuel from flowing from the float bowl to the carburettor henceforth stopping the engine.

Whilst the engine is running manifold vacuum is applied to the carbon canister. Air flows into the intake of the solenoid through the canister and in doing so collects petrol fumes from the carburettors and the fuel tank. When the engine is switched off the solenoid is activated sealing of the inlet and applying full manifold vacuum to the canister. This in turn applies a partial vacuum to the float bowls of the carburettors preventing fuel flowing from them into the carburettor jets thus stopping the engine. If the valve is not working then it will be apparent by the engine running-on. When the engine has stopped and the oil pressure has dropped to zero the solenoid is deactivated and the engine is ready to for operation again.

If your engine runs on then a quick system check can be made by removing the wires from the solenoid and connecting 2 wires from the battery to the solenoid which, if working correctly, will cause the engine to stall.

A check of the electrical ciruit which feeds the solenoid will be required if the above test indicates that the solenoid is ok. Connect a test lamp across the solenoid and start the engine. When the engine is turned off the lamp should come on for a few seconds untill the engine stops and oil pressure is lost. If the lamp fails to operate then further investigation of the electrical fault will be required.

Check that the original 3 pin oil pressure switch has not been repalced with a conventional single pin version which will not provide the correct operation. The 3 pin oil pressure switch contains 2 switches, one to indicate low pressure and drive the oil light as per a single pin oil pressure switch and a second switch to indicate the presence of oil pressure which is used by the solenoid.

Locate the change over relay mounted under the dash and check that there is power to the relay and that it operates when the ignition is turned on. When the ignition is turned off the relay releases and it makes a connection from the battery to the solenoid.

 If the engine is running (oil prressure present) and the ignition is turned off the oil pressure switch provides the earth connection to the solenoid and the relay provides the power to the solenoid which should stop the engine. When the engine stops turning and the oil pressure drops, the oil pressure present switch will turn off along with the solenoid.

© Adrian Diehm TSOAQ