Manufacturers worldwide are moving to eco-friendly productions to help reduce the emission of polluted air. Automobile manufacturers do their part to help reduce emissions into the atmosphere by developing the Evaporative Emission Control(EVAP) system. Gasoline contains highly volatile hydrocarbons, which can escape into the atmosphere, leading to wastage of usable fuel and air pollution. Therefore, the EVAP system works to store these hydrocarbons and release them into the engine for combustion.
This makes every part of the EVAP system an integral component in emission control. One of these parts includes the purge valve. Failure of the purge valve is quite significant in that it can negatively affect the engine and its performance. In our article below, we have described the work of a purge valve, common signs of a faulty one to help you understand its importance, and the need to replace it when it fails to keep your car in good condition for longer.
What does a purge valve do in your engine?
The purge valve, also known as a canister purge valve or solenoid, is vital for the Evaporative Emission Control (EVAP) system. The EVAP system seals the fuel system in your vehicle to restrict harmful fuel vapors from entering the environment and temporarily traps them in a charcoal canister.
When your car engine is running at a regular speed, the EVAP system starts to slowly release this vapor from the charcoal canister into the engine to burn like regular fuel. The purge valve is an electronically operated solenoid that controls the flow of these vapors. It regulates when and how much of these vapors enter your engine.
How do i know if my purge valve is bad?
Like other automotive parts, the purge valve will wear down over time and become inefficient or can even crack from harsh environmental conditions. The purge valve can also go bad due to accumulating dirt and dust from regularly driving, therefore clogging the canister.
When the purge valve becomes bad, it either sticks or doesn’t close fully. Below are the signs and symptoms to look out for when the purge valve is not functioning correctly.
Check Engine light is on.
The first sign that the electrical part of your purge valve is failing is the Check Engine light illuminating. When the purge valve goes bad, the car’s computer will detect the abnormal purging from the valve and trigger the Check Engine light. When you connect the ODBII scanner, you’ll likely see the error codes P0443, P0445, P0458, and P0459, but the codes may vary depending on the car brand.
Rough idling
A bad purge valve will create a small vacuum leak, leading to a rough idle, especially when temporarily stopping. A broken purge valve or any hoses attached to it will also cause the vacuum leak, leading to the engine running at an inconsistent speed. You will most likely have an oxygen sensor code for a lean mixture. You should address this issue immediately to prevent the engine from stalling completely.
Check this too: Why Is My Engine Idling Rough?
Difficulty in starting
The vacuum leak created by the faulty purge valve will cause trouble when starting the car. It will cause the excess air from the outside to enter the engine and interfere with the overall combustion process. So although your vehicle will still start, it will take longer than usual to get there.
Poor engine performance
You should expect to experience a weaker engine performance when your purge valve fails. This is because when the purge valve becomes stuck open, more air gets into the engine. More air in the engine interferes with the correct fuel to air ratio for combustion, therefore preventing your engine from generating the much-needed power for acceleration when depressing the gas pedal. This issue will be most evident when going uphill or overtaking other vehicles.
Poor fuel economy
Typically, a functional purge valve transfers fuel vapors amounting to about 5 – 10% of the fuel mixture burned in the cylinders. Thus, a blocked purge valve will cause the fuel vapors your car uses for combustion to be vented through the EVAP canister and into the environment instead. These vapors will not reach the combustion chamber; therefore, your engine will only use fuel from the gas tank for combustion. This means your vehicle will not use its fuel efficiently.
How to test a purge valve
Using the following instructions, you can test if a purge valve is working using a multimeter to test for resistance between the terminals. The process for testing a purge valve will vary between different car models, but the basic steps are the same.
- Switch off the engine and let it cool down for about 30 minutes.
- Locate the purge valves of your vehicle. Ideally, the purge valve is either behind the muffler or positioned on top of it. There you will find the EVAP charcoal canister, and the purge valve is inside it.
- After locating the purge valve, you will see a 2-pin harness connecting to the valve. Disconnect the harness and reconnect purge terminals to the multimeter’s adapter cables.
- The multimeter should give you a reading. Usually, the multimeter reading should be between 22 ohms and 30 ohms to indicate the purge valve is working correctly. If the reading is below or above this range, your purge valve has an issue and will need replacing.
What happens if your purge valve is stuck closed?
Once the purge valve gets stuck in the closed position, it prevents the EVAP system from releasing the fuel vapors in the charcoal canister to the engine for combustion. It will lead to poor gas mileage and cause premature charcoal canister failure. The fuel vapors will come out of the exhaust and generate higher emission levels.
Can i keep driving with a bad purge valve?
Driving your vehicle with a faulty purge valve is certainly possible, but we do not recommend it. It may not be as urgent as other problems, but it helps address the issue as soon as you notice it. Here are some of the things that happen when you do not replace a bad purge valve:
- Driving with a bad purge valve increases the risk of damaging your vehicle’s EVAP system and other parts, such as spark plugs and gaskets.
- You also run the risk of wasting fuel and releasing more emissions than is necessary.
- There will also be implications for your engine. For instance, a bad purge valve causes your engine to run on fuel mixed with excess air, negatively affecting its performance. As a result, your car engine is likely to misfire frequently and lead to stalling.
- The inconsistent running of your engine caused by the bad purge valve will create stress on the engine’s internal components, and it will lead to premature engine failure.
- Driving with a bad purge valve for too long will also cause carbon build-up on the cylinders and heads of the engine. This carbon build-up can prematurely destroy your engine, cause loss of fuel economy, stalling, engine knocking, and overheating. Eventually, failure to fix the bad purge valve will mean more expensive repairs.
- Another concern about driving with a bad valve is the Check Engine light will always be on. If you do not fix the issue, you will not know when another major problem arises.
- A bad purge valve will lead to a failed emissions test, costing you fines. You will also need to pass the emissions test every time you renew your insurance.
How long can you drive with a bad purge valve?
How long you can drive with a bad purge valve depends on many variables. For example, if you’re a lover of high speeds, you may not enjoy that for long as engine performance will reduce significantly after the purge valve fails.
As previously mentioned, the purge valve redirects fuel vapor back to the engine to keep them from coming out through the exhaust. So if the purge valve fails, your vehicle will fail the emission test. Failing a state emission test can prevent you from securing a certificate at the Department of Motor Vehicles(DMV). You will be unable to drive your vehicle legally in the US and UK. It is illegal to drive a car that doesn’t comply with the emissions requirement with fines up to $77.
Driving with a bad purge valve will also release fuel vapors into your vehicle cabin, which is a health hazard. Inhaling these fumes can cause headaches, dizziness, and other respiratory issues. Therefore how long you can drive with a bad purge valve will depend on how long you’re willing to tolerate these symptoms. However, we advise against inhaling any amount of fuel vapors. All these issues notwithstanding, you can drive a vehicle with a bad purge valve for a while before the car breaks down completely.
How to bypass a purge valve
The canister purge valve is an essential component of the emissions system that allows efficient fuel consumption and reduces air pollution. However, some car owners experience too many car issues due to a bad purge valve that they decide to bypass or delete the purge valve altogether. Here’s how you can bypass the purge valve and release the fuel vapors to the environment.
- Locate the purge valve and disconnect the lower hose that connects to the charcoal canister.
- Plug the fuel tank vent line directly into the purge valve.
- Find the hose that runs from the airbox to the charcoal canister. Then pull this hose and cap it.
- Unplug the pressure sensor by disconnecting the charcoal canister completely.
Although bypassing the purge valve is possible, you will still experience issues such as:
- Check Engine light. The vehicle’s computer performs a series of leaking and venting tests by activating different EVAP system valves. In the absence of the purge valve, the computer will not detect the required vacuum decay.
- Poor fuel economy.
- Shaky vehicle idle
- Vapor escape in the atmosphere will cause fuel smell all around and inside your car, which can also be a fire hazard. In addition, a spark from engine ignition can quickly light the fuel vapor in the air.
- It could be illegal in your area
How long does a purge valve last?
Usually, the purge valve should last as long as the vehicle, but it will wear out every few years like other automobile components. It has no set lifespan; when it fails, it remains stuck open or closed and creates further issues in the engine. When the purge valve malfunctions, you’ll need to replace it. The purge valve works by reacting to the vapor vacuum in the charcoal canister by opening and closing. The purge valve won’t function if the charcoal canister or its supply lines are blocked or worn out. Also, the valve’s electrical component can fail and cause it to remain closed.
How to fix a bad purge valve
As explained above, when you notice the signs of a bad purge valve and you can no longer drive with a faulty one, a purge valve replacement is the best solution. Unfortunately, it will cost you between $70 to $200 to replace a bad purge valve depending on the car model, model year, and where you buy the parts. However, if you have some basic automobile experience and tools, you can replace them yourself by following the instructions below.
Things you need
- Ratchet wrench
- Flat blade screwdriver
- Penetrating oil or WD-40
- Replacement purge valve
- Replacement vacuum hoses(needed if the current hoses are damaged)
- ODBII scanner
Directions
- Disconnect the car battery.
- Lift the hood and locate the purge valve. The position will vary depending on the make and model of the vehicle. You are likely to find it on top f the engine or near the back of the fuel system.
- You will see an electrical harness and two vacuum lines attached to it. One vacuum line runs to the fuel injector rail, and the other goes to the EVAP canister near the fuel cell.
- Match the faulty purge valve to the replacement piece and mark the location of each vacuum line to avoid installing them backward.
- Then unplug the electrical harness attached to the valve.
- Disconnect the vacuum lines using the wrench.
- Remove the bad purge valve by removing the bolt securing it.
- Install the new purge valve on the product packaging.
- If necessary, replace the new vacuum hoses on the valve and ensure the male fittings are correct.
- Install the electrical harness.
- After installation, check the vacuum lines to ensure they are not backward, as incorrect installation can cause severe engine damage.
- Reconnect the battery cables and start the engine. Then clear any error codes with the scan tool.
- Start the vehicle and allow it to warm up to operating temperature. Next, check the dashboard for the Check Engine light. If the light comes on, shut the vehicle and perform a diagnostic scan.
- If the light stays off, shut off the engine and remove the gas cap to verify the vacuum is working. If the vacuum pressure is high, inspect the purge valve vacuum lines to be crossed or kinked.
Conclusion
The canister purge valve or solenoid prevents harmful gas vapor from releasing into the atmosphere while also improving gas mileage. However, a bad purge valve will cause fuel wastage, rough idling, poor acceleration, and reduced engine performance. If you notice any signs of a bad purge valve, including a failed emissions test, you should replace the valve to avoid further damage to the engine and for smooth driving.