If you’re wondering why your car smells like a cross between rotten eggs and an entire oil refinery even with the fuel cap sealed shut, then you may want to check your purge valve.
A bad purge valve can start leaking fumes like there’s no tomorrow, but based on our experience working with these little “suckers”, there’s even more to them than meets the eye (or nose).
So if you want to catch and fix a bad purge valve early, heighten up your senses to all the other common symptoms we’ll be going over in this guide, and just maybe you can even light a cig safely within fifty feet of your car after to celebrate.
What are the symptoms of a bad purge valve?
Symptoms of a bad purge valve include the engine struggling or failing to start, a check engine light (CEL), the smell of fuel vapor, and overheating problems.
A bad purge valve may cause the engine to run rough or stall, delayed acceleration, black exhaust smoke or fluid, and reduce fuel economy.
Purge valves can start showing many different symptoms once they go bad, though some of them may not be as noticeable for those experiencing them for the first time.
As a small yet important component of the EVAP system, a bad purge valve is something that should be addressed immediately before it starts to affect other parts of the system and rack up potential repair costs even further.
1. Engine Struggles to Start or Doesn’t Start
If you have a bad purge valve on your vehicle, then your engine’s performance will be negatively affected one way or another.
You may notice that starting the engine can sometimes be difficult or takes a while to start, or other times, it may not even start at all.
To understand how a bad purge valve affects an engine’s ability to start, we need to look into the positive pressure that builds up in the fuel tank.
One task of the purge valve is to make sure that the positive pressure in the fuel tank is maintained even when the engine is turned off.
This positive pressure is essential in preventing the fuel from flowing back into the filler pipe, and it also prevents excessive air from going into the intake.
However, a bad purge valve that’s stuck open even while the engine is off will draw in too much air and mess up the delicate air-fuel ratio inside the engine during startup.
2. Engine Runs Rougher Than Usual
While a bad purge valve may not immediately affect engine performance at the start, keep the engine running long enough and you may start to notice it idling rougher than usual. Not that we recommend waiting that long to test it out, by the way.
However, for those who have had the misfortune of not noticing any other symptom earlier, a bad or damaged purge valve can start a vacuum leak that affects the amount of air that is permitted to enter the engine.
With more air entering the engine, the vehicle’s computer (ECU) will try to compensate for this by altering the air-fuel ratio, and you may feel that the engine is not running as smoothly and consistently as it was before.
But again, a rougher running or idling engine can be caused by many reasons, such as issues from even the ignition system and fuel system. As much as possible, this symptom should be in the presence of the others listed here as well.
3. Engine Suddenly Stalls
There is a chance that your engine can also suddenly stall if you keep driving long enough with a bad EVAP canister purge valve on your car.
This all goes back to the situation that if a purge valve goes bad, it can get stuck in the open position and allow too much fuel vapor to enter the engine, causing the engine to run too rich.
Depending on how rich the engine gets and how bad the condition of the purge valve is, you may experience either intermittent or consistent stalling problems.
4. Illuminated Check Engine Light (CEL)
Since we’re already aware that a bad purge valve can affect how your engine performs, it can also cause your vehicle’s ECU to trigger the check engine light (CEL) on your dashboard.
However, a bad purge valve is only one of the many different things that can cause a check engine light, which is why this symptom should be paired with the many other symptoms that we’ve listed here.
Otherwise, you can also ask help from a mechanic to scan your vehicle’s ECU for error codes if a check engine light appears, as such codes will be able to confirm if it really is an issue with your purge valve or EVAP system.
Common error codes for a bad purge valve or EVAP system issue include P0441, P0443, and P0446, all of which you can read by using a diagnostic tool such as an OBD-II reader on your vehicle’s ECU.
5. Fuel Vapor/Gasoline Smell From the Engine
One symptom of a bad purge valve requires you to have a sense of smell (shocking) to notice it, as a bad purge valve will give off the smell of fuel vapor or gasoline coming from the engine.
The fuel vapor smell can specifically come from the purge valve leaking excess vapor because it is unable to keep it sealed and contained within the EVAP system.
The smell is especially more obvious when you’re actually driving around, though it can also pop out more by simply being in colder conditions.
However, the smell of fuel vapor can also come from your other EVAP system components, so it’s also worth checking things like your charcoal canister, vacuum feed line, vacuum control valve, or fuel filler tube for any leaks.
6. Engine At Risk of Overheating
If your purge valve starts acting up for some reason, then there’s also the possibility that your engine can overheat. However, a bad purge valve isn’t necessarily the direct reason for an overheating engine, and you’re about to know why.
Since a purge valve is tasked to control the amount of fuel vapor being directed back into the engine, a failure in the component would mean that excess fuel vapor would be released, leading to a richer fuel mixture inside the engine.
The longer that you use your car with a bad purge valve that remains open, the more fuel vapor will be present inside the engine, resulting in an increased buildup of carbon deposits. This is more likely to happen at idle or lower speeds.
It is through this increase in carbon buildup that the risk of running your engine at higher temperatures becomes more likely. If not resolved right away, the engine can eventually overheat and even start knocking.
7. Delayed Acceleration
When we said that a bad purge valve can affect your engine’s performance, we weren’t kidding, as an engine running with a malfunctioning purge valve can start to exhibit delays in acceleration.
However, acceleration performance only usually gets affected if the faulty purge valve has already gone bad enough to cause other related problems like vacuum leaks, an imbalanced air-fuel ratio, and rougher idling.
In the case of a normal functioning purge valve, it will be able to regulate the amount of fuel or vapor entering the engine and preserve the correct air-fuel ratio, which leads to optimum performance, of course.
With a bad purge valve, all of that goes out the window, and so does a smooth-performing engine that doesn’t hesitate when you put the pedal to the metal.
8. Black Exhaust Smoke or Fluid
Bad purge valves are known to increase your vehicle’s emissions because of the escaping or leaking of fuel vapor alone, but did you know that it can also cause black smoke or fluid to come out of your exhaust?
If your purge valve is not doing its job of keeping the right amount of fuel vapor entering the engine at a time, then it can let in too much of it and make your engine run rich.
With a richer fuel mixture, some of the fuel will be left unburnt by the engine and eventually end up in the exhaust, which will be in the form of black smoke emissions.
9. Reduced Fuel Economy
Another common symptom of a bad purge valve is reduced fuel economy. In the case of a purge valve that creates a vacuum leak, it can let in too much air into the engine, which will yet again affect the air-fuel ratio of the engine.
And of course, if the correct air-fuel ratio in a specific engine is not followed, the ECU may adjust by either adding or reducing the amount of fuel injected. In this case, since you’re getting more air with a vacuum leak, you’ll be using up more fuel.
What is a purge valve on a car?
A purge valve (or canister purge valve) is a component of a car’s EVAP (Evaporative Emission Control) system that sucks in fuel vapor from the fuel tank and releases it into the engine.
Purge valves are small plastic devices (usually black in color) that are tasked to control the flow of fuel vapor going into the engine for combustion.
As part of the EVAP system, the purge valve is considered an emission control device that prevents fuel vapor created in the fuel tank from leaking into the outside air.
How does a purge valve work?
A purge valve is electronically operated by a solenoid, which opens up according to the vehicle’s computer (ECU).
Once opened, the purge valve lets fuel vapor flow from a charcoal canister after the fuel tank and into the intake and engine, getting burned and reducing emissions in the process.
Purge valves are specifically programmed to open and close at a calculated amount of time while the engine is running, so absolute balance is key in it doing its job right.
If the purge valve either takes too long to open up and close or gets stuck in one position, this can significantly affect the flow of fuel vapor and air into the engine and even throughout the EVAP system.
Hence, any hiccup from the purge valve can cause a cascade of issues concerning your engine’s performance, emission levels, and other affected components.
Where is the location of the purge valve?
The canister purge valve is commonly located either next to the fuel tank or in between the intake and the canister connected by hoses.
In some vehicles, the purge valve will look like a small, black cylinder next to the vehicle’s engine block, where its hoses go toward either the intake or canister.
The exact location of a purge valve can vary between different vehicle models, but one thing that you can be sure of is that it’ll be interconnected with other parts of the Evaporative Emission Control (EVAP) system.
If you look at a diagram of an EVAP system, you’ll see that the purge valve is connected to a container-looking part called a “charcoal canister”, which is what actually absorbs and stores the fuel vapor from the fuel tank.
The other side of the purge valve will be connected to your intake manifold, the point where the fuel vapor enters at a controlled pace in order to be combusted with the rest of the fuel.
What causes an EVAP purge valve to go bad?
An EVAP canister purge valve can go bad due to a faulty solenoid, faulty wirings or connectors, being dirty or getting clogged, leaking issues, or a faulty ECU (engine control unit).
Bad Purge Valve Solenoid
Whenever a purge valve goes bad, it’s worth checking the solenoid that actually controls the opening and closing of the component.
A faulty purge valve solenoid is one of the most common reasons why a purge valve either doesn’t open up or close on time or gets stuck in one position the entire time.
Faulty Purge Valve Wirings or Connectors
The purge valve is an electronically controlled component, so any damage that happens to its wirings or connectors can cause it to malfunction or completely stop working.
Thus, if you find out that your purge valve is slow to open up and close or has stopped moving, then be sure to inspect its wirings and connectors for signs of wear.
Dirty or Clogged Purge Valve
The purge valve lets fuel vapor pass through it every time the engine is running, and while it may not exactly be a solid state of matter, fuel vapor can eventually create a buildup of fuel deposits that can stick to the purge valve.
Even other things such as dirt, dust, or corrosion can form on the purge valve opening, and if it becomes worse enough, it can partially or fully block the flow of fuel vapor toward the engine.
The good news is that you can clean a blocked purge valve, though you first need to unplug all of the connecting hoses and wires to actually take a look inside.
Depending on the contaminant and how blocked it is, you can use either a vacuum cleaner, a carb or MAF cleaner, or a brush to remove any debris that has built up on the purge valve.
Purge Valve Leaks
If there is a leak present in the purge valve or any of its hoses, then it will not be able to keep the correct flow of fuel vapor through it, which means that you will be losing positive pressure within the EVAP system as well.
Maintaining positive pressure is another important job of the purge valve that prevents the fuel from flowing back into the filler pipe, so if there’s a vacuum leak somewhere, the purge valve will fail to do its job even when the engine is off.
Faulty Engine Control Unit (ECU)
At other times, a purge valve becomes bad not because of an internal fault, but because of the one that’s actually commanding and controlling it, the vehicle’s engine control unit (ECU).
Like many other electronic components, the purge valve is programmed to operate according to what the ECU receives from the different sensors in the EVAP system.
For instance, if a sensor detects that there’s a change in the pressure in the EVAP system, then the ECU may change the timing that the purge valve opens or closes.
However, if the ECU itself is malfunctioning, then it may detect a false positive and command the purge valve to unnecessarily operate a certain way, which can potentially cause it to malfunction as well.
How to Test a Purge Valve
To test if an EVAP purge valve is still working, you can use a multimeter and some adapter cables to perform a resistance test on its terminals.
Alternatively, you can disconnect the canister side of the purge valve to see if the opening is still pulling in air while the engine is running.
Resistance Test
How to Test Purge Valve With a Multimeter (Resistance Test):
Locate Purge Valve – When locating the purge valve, the engine should be turned off and cooled down first. The purge valve is a small black component usually located next to the fuel tank or in between the intake and the canister.
Unplug Harness from Purge Valve Terminals – The purge valve has a 2-pin harness connector that needs to be disconnected in order to access its terminals.
Connect Multimeter to Purge Valve Terminals – Connect or touch the ends of both the multimeter’s adapter cables to the purge valve terminals where you have unplugged the connector.
Do a Resistance Test for the Terminals – Test for resistance between the two terminals by selecting “ohms” (omega symbol) on the multimeter. If it doesn’t read between 22 and 30 ohms, then you have a bad purge valve.
Checking for Vacuum
Just in case you don’t have a multimeter or any other tools with you, another simple way of testing if a purge valve still works is to disconnect the hose that’s connected to the charcoal canister.
You will be checking if the purge valve actually works by feeling with your fingertips if the opening is still sucking in air or “pulling vacuum”. Of course, it’s important that you keep the hose going to the intake still plugged in while testing this.
Ideally, you want to make sure that the engine is turned off and cooled down first before actually pulling off the canister hose, as you would want to test if the purge valve starts in a closed position while the engine is off.
Afterward, you can start the engine and let it warm up for a few minutes. As the engine warms up, a normal functioning purge valve should start to open up to let fuel vapor flow from the canister to the intake at the other end.
However, if it fails to open up and you don’t feel any vacuum after the engine has warmed up, then you’ve got a bad purge valve.
Similarly, if the purge valve immediately pulls in the air as you start the engine, then that’s not good either since it may be stuck open the whole time.
Frequently Asked Questions (FAQs)
