Why You Absolutely Shouldn’t Drive with an EVAP Leak
Purging gas ain't just for after you eat beans.
Sometimes, a check engine light pops up and it’s no big deal. It could be a faulty sensor or you could’ve been a tool and forgotten to tighten your gas cap enough. But sometimes there’s a problem that requires your immediate attention. If not, well, you’re looking at sitting by the side of the road, waiting for a tow and cursing the car gods. You know, the one’s responsible for direct-port nitrous injection, four-core intercoolers, ball-bearing turbos, and titanium valve springs.
One such issue that can’t be ignored is the purge valve, which can cause issues with your car’s idle, fuel economy, and performance when it starts to fail. You’ll also have to stare at a check engine light until you get the problem fixed. And WE all know how annoying and confidence-sucking that can be.
Thankfully, replacing a bad purge valve is both easy and somewhat cheap, so there’s no real reason to ignore it. If you’ve never heard of a purge valve, stick with Car Bibles’ HQ, and we’ll take you through the ins and outs of purge valves, what happens when they fail, and what it takes to replace them.
What Is a Purge Valve?
Purge valves are part of a vehicle’s evaporative emissions control system (EVAP), which works to prevent fuel vapors from escaping the fuel tank. The system stores those vapors in a canister and purges them to be burned in the engine’s combustion cycle. The purge valve itself, however, controls the amount of vapor that is released.
How Does a Purge Valve Work?
The purge valve is an electrically-controlled solenoid, which remains closed while the engine is off. When the engine is running and up to temperature, the vehicle’s ECU (electronic control unit) and sensors monitor the purge flow and regulate it using the purge valve. If something goes wrong, the system might kick a check engine code to alert the driver of improper purge flow.
What’s the Difference Between a Purge Valve and a Purge Solenoid?
Your gearhead buddy tells you it’s the purge valve, then you head to the shop for a second opinion, and they tell you it’s the purge solenoid. Before you jump to the conclusion that one of them doesn’t know what they’re talking about, you should know that they mean the same thing. Like many other automotive parts — engine block/cylinder block, for example — it can go by two names.
Symptoms of a Failing Purge Valve
Purge valves are relatively simple devices, so there’s not a whole lot that can go wrong. The most frequent issue with purge valves is that they can stick open or closed. A stuck purge valve will cause the check engine light to come on in most cases. When it does, you’re in luck because a trouble code will tell you exactly what’s going on. A check engine light that’s warning you of a faulty purge valve shouldn’t be ignored, though. They may be simple, but they can inspire some alarming problems.
It’s important to understand that the purge valve taps directly into the intake manifold. A purge valve that’s stuck open cannot seal the manifold from outside air, meaning you have a vacuum leak on your hands. As you may already know, vacuum leaks inspire a number of engine issues. Hard starting, rough idling, misfires, and poor overall engine performance due to a lean air-fuel mixture can all be linked to the vacuum leak a stuck purge valve creates.
Before you decide to replace the valve, keep in mind that a simple hose connects the purge valve to the intake manifold. It’s worth looking at the hose to make sure it’s not disconnected or cracked, which will also cause a vacuum leak.
Thankfully, a purge valve that is stuck closed won’t pose any issues to performance. Still, you shouldn’t ignore the problem because it’s unable to do its job and control emissions.
How Much Does It Cost to Replace a Purge Valve?
The average cost to replace a purge valve is between $150 and $200, but yours could cost more or less, depending on the location and difficulty of replacing the valve. And if you have a trained mechanic replace it, you’ll have to pay for labor.
Car Bible’s Glossary for Purge Valve
Welcome to Bible School!
Idle refers to the vehicle’s engine speed when it’s not in motion. It should be consistent and steady.
In order for an engine to run properly, it requires a precise mixture of both oxygen and fuel to maintain combustion. If one part of the equation is out of balance, the engine can run rough or have trouble starting.
EVAP, or evaporative emissions control systems, are part of a vehicle’s emissions systems that prevent fuel vapors from escaping into the atmosphere.
FAQs About Purge Valves
Let Car Bibles answer all your burning questions!
Q. How Is the Purge Valve (Solenoid) Tested?
A. This process will vary based on the type of car, but in many cases, it’s possible to apply voltage and observe the valve’s behavior. When it receives power, it should produce an audible sound. Further testing of the valve’s seals is to apply vacuum and observe the vacuum levels.
Q. How Long Does a Purge Valve Last?
A. In most cases, the purge valve should last for the life of the vehicle. Over time, the seals can wear and moving parts break down, so it’s not guaranteed that you’ll get unlimited time from your purge valve.
Q. Where Is the Purge Valve Located?
A. This will vary depending on the vehicle, but in most cases the purge valve is located on top of the engine near the fuel system.
Video on Purge Valve
Car Bibles understands that many of you aren’t text-based learners, preferring a kinesthetic approach. We got your back and pulled a video from one of our trusted sources to help you understand what a purge valve does and how it works.
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