Where is the purge valve located in a car?

This blog will answer the following questions: where is the purge valve located in a car? What is the function of the purge valve? What are the requirements for the Purge function? Which components are used in the purge system? What are the common problems associated with the fuel vapor purge system?

Where is the purge valve located in a car?

The purge valve is located near the left or right side of the engine, it is connected to a purge line. The purge line is routed with the fuel line from the fuel tank. It is used to carry the fuel vapors stored in the charcoal canister. The output of the purge valve goes to the intake manifold. It is connected downstream of the throttle valve.

The purge valve or purge control valve is only present in vehicles powered by gasoline engines. It is mandatory for all gasoline-powered cars to have a purge vapor system. Releasing the fuel vapors in the tanks directly into the environment is no longer permitted.

Usually, the purge valve is located near the intake manifold but in some models, it can also be present near the fuel tank. Replacing the purge valve near the fuel tank is difficult as the rear wheel and fender lining must be removed to disconnect the hoses connected to the purge valve.

It takes only a few minutes to replace the purge valve if it is located near the engine. On vehicles with high mileage, the hose can crack as it is weakened due to heat from the engine. There are also metal locks on the electrical coupler of the purge valve to prevent any loose connection.

What is the function of the purge valve?

The function of the valve is to purge the fuel vapors that are stored in the charcoal canister. When the purge valve is opened, the vacuum from the intake manifolds sucks the fuel vapors in the hose and purge lines. 

The charcoal canister is restricted in size because they are installed in a wheel arc near the fuel filler neck. They cannot hold large quantities of fuel vapor and must be purged regularly. A blocked charcoal canister can cause a drop in the fuel pressure in the low as well as the high-pressure fuel system.

The purge valve is actuated by a PWM signal from the engine control unit. The frequency of the PWM signal is 10 Hz and the quantity is determined by continuously opening and closing the purge valve.  As the fuel vapors can enrich the air-fuel mixture, the engine control unit also reduces the fuel injection quantity when the purge valve is open. 

As soon as the purge valve closes, the oxygen sensor detects the lean mixture, and the engine control unit can again increase the fuel injection quantity. There is only an activation line to the purge control valve; the engine control unit uses the lambda control to purge the fuel vapor.

Therefore, the purge valve is not operated until the exhaust temperatures are high and the oxygen sensors are ready. The engine control unit can actuate the oxygen sensor heater to bring the sensors into operating range more quickly. The purging function is only active in the partial load range, the purge valve is closed in the full load condition.

What are the requirements for the Purge function?

The requirements for the Purge function are given below, the engine control unit does not activate the purging function until all the requirements are satisfied:

• The engine must be running for at least 45 sec 
• the circuit 87 M signal should be ON.
• Coolant temperature should be greater than 40-degree celsius.
• The engine load is in a partial range 
• The engine must not be in deceleration mode
• The Lamba adaptation must be completed 

Which components are used in the purge system?

The components that are used in the purging system are given below

Fuel tank

The fuel vapor inside the tank is not allowed to escape into the atmosphere, therefore the fuel tank consists of aeration or vent valves. When there is a buildup of fuel vapor in the fuel tank, the vent valves open, and fuel vapor enters the hose leading to the activated charcoal canister.

There are additional hoses in the fuel filler neck, it catches the fuel vapor present in the fuel filler neck when the vehicle is refueled. Purge hoses are a combination of rubber and plastic hoses and they are routed close to the fuel tank to avoid damage by coming in contact with any moving part.

Depending on the size and the capacity of the fuel tank, there can be two to three vent or breather valves. The breather valves are non-return, once the fuel vapor enters the hose it cannot come back inside the tank.

Activated Charcoal canister

The canister is connected to the fuel tank vent valves. Fuel vapors are collected and stored in the charcoal canister. When the purging function starts, fuel vapors are extracted from the charcoal canister and supplied to the engine where they are burned in the combustion chamber.

The canister is also connected to the air admission and vent line, it goes to the fuel filler neck and collects any fuel vapors present in the neck. The size of the charcoal canister is restricted and depending on the mileage of the vehicle, it may need replacement. 

Purge valve

The purge valve is the last component in the purging system. It is connected to the charcoal canister and works when the ECU provides the ground signal. When the purge valve is actuated with the help of an OBD II diagnostics tool, audible noise can be heard. 

If the noise does not come it means the purge valve is either stuck or not working. The purge valve is made up of a simple electrical solenoid, when the solenoid is open vacuum from the intake manifold is connected to the purging system.

The vacuum from the intake manifold sucks the air through the air admission line connected to the charcoal canister. The air carries the fuel vapors from the canister so that more vapor can be stored in it.

What are the common problems associated with the fuel vapor purge system?

The common problems associated with the fuel vapor purge system are as follows:

• Faulty purge valve
• Leak in the purge line 
• Blocked charcoal canister.

When a fault occurs in the purge system, the engine malfunction light turns ON. there can be fluctuations in the idling speed of the engine. In some cases, a blocked canister can also cause a drop in fuel pressure.

Conclusion

This blog explained the Purging system in the gasoline engine and also listed its key components. The faults related to the purging system are not expensive to repair. Therefore, it is important to get the vehicle checked if it is showing an engine check light or poor idling.