4. How Does Vacuum Decay System Work

---

Introduction

---

How Does Vacuum Decay System Work:

The EVAP Vacuum Decay system might sound like a big, complicated thing, but it's not! In this easy-to-understand explanation, we'll break down how it works, so even a 6th grader can get it.

How Does Vacuum Decay System Work:

What is the EVAP Vacuum Decay System? The EVAP Vacuum Decay system helps the PCM to determine if there is a leak in the EVAP system. It's there to help keep the environment clean.

How Does It Work? Imagine you have a special tank in your car called the "gas tank." This tank holds all the gasoline your car needs to run. But sometimes, gasoline can turn into gas vapor, and that's not good for the environment. That's where the EVAP Vacuum Decay system comes in.

Step 1: Capture the Gas Vapor The system has a special canister that captures the gas vapor from the gas tank. It's like a vacuum cleaner that sucks up the vapor and stores it safely, "EVAP Canister". 

Step 2: Sealing the Gas Tank, Your car's gas tank needs to be sealed tight, like closing a lid on a jar. If there are any tiny leaks, the EVAP Vacuum Decay system will find them. It checks to make sure no vapor escapes into the air.

Step 3: Testing for Leaks Sometimes, the system needs to check if everything is sealed properly. It does this by creating a vacuum, like sucking the air out of a balloon. If the vacuum stays strong, it means everything is sealed well. But if it drops, "pressure increases" it means there's a tiny leak, like a hole in the balloon.

Step 4: If the system finds a leak, it tells your car's computer, which the technician then needs fix it. This helps keep the gas vapor from escaping into the air and polluting the environment.

Why Is It Important? The EVAP Vacuum Decay system is essential because it helps reduce pollution and makes sure your car runs efficiently. It's like a guardian for the environment and your car's performance.

So, there you have it! The EVAP Vacuum Decay system is like a super-helper for your car, making sure it runs well and keeps the air clean. It's not as complicated as it sounds, right?

---

---

H20, PSI Hg and KPA Explain

---

How Does Vacuum Decay System Work

How Does Vacuum Decay System Work:

1. H2O stands for "water." It's a way to measure how much water pressure there is in a system.
2. PSI stands for "pounds per square inch." It's another way to measure pressure, like how much air or water is pushing on something.
3. Hg stands for "inches of mercury." It's an older way to measure pressure, but it's still used sometimes. It's like measuring how high a column of mercury (a type of liquid metal) gets pushed up in a tube by the pressure.
4. kPa stands for "kilopascals." It's another way to measure pressure, like PSI, but it's used in the metric system, which is what most of the world uses.

Now, let's see how they relate when testing the EVAP system:

When testing the EVAP system, we're looking for leaks or problems in the system that controls gasoline vapor (the gas that comes from your car's gas tank). We use different pressure measurements to do this.

• H2O (Water Column): This is often used when testing the EVAP system because it's a sensitive measurement. For example, if we apply 1 inch of water column (1 inch H2O) pressure to the system, we can see if there are any leaks. If the water level drops, it means there might be a problem.
• PSI (Pounds per Square Inch): Some EVAP tests use PSI. For instance, if we apply 1 PSI pressure to the system, we can check if it holds that pressure. If it doesn't, there might be a leak.
• Hg (Inches of Mercury): In some older tests, Hg is used. If we apply a certain amount of Hg pressure to the system, we can see if it holds that pressure. If the Hg level falls, it suggests a problem.
• kPa (Kilopascals): In places that use the metric system, like many countries outside the United States, kPa is commonly used. For example, if we apply 10 kPa pressure to the EVAP system, we can check if it stays at that level. If not, there might be an issue.
• mmHg: stands for "millimeters of mercury." It's like inches of mercury, but it measures pressure in millimeters instead of inches.

So, all these measurements are like different languages to talk about pressure. They help us find problems in the EVAP system and make sure your car runs smoothly and doesn't pollute the environment with gasoline vapors.

---

---

How does this relate to Testing 

---

How Does Vacuum Decay System Work:

When testing the EVAP system, we're looking for leaks or problems in the system that controls gasoline vapor (the gas that comes from your car's gas tank). We use different pressure measurements to do this.

• H2O (Water Column): This is often used when testing the EVAP system because it's a sensitive measurement. For example, if we apply 1 inch of water column (1 inch H2O) pressure to the system, we can see if there are any leaks. If the water level drops, it means there might be a problem.
• PSI (Pounds per Square Inch): Some EVAP tests use PSI. For instance, if we apply 1 PSI pressure to the system, we can check if it holds that pressure. If it doesn't, there might be a leak.
• Hg (Inches of Mercury): In some older tests, Hg is used. If we apply a certain amount of Hg pressure to the system, we can see if it holds that pressure. If the Hg level falls, it suggests a problem.
• kPa (Kilopascals): In places that use the metric system, like many countries outside the United States, kPa is commonly used. For example, if we apply 10 kPa pressure to the EVAP system, we can check if it stays at that level. If not, there might be an issue.
• mmHg (Millimeters of Mercury): This is similar to inches of mercury, but it measures pressure in millimeters. For instance, if we apply 10 mmHg pressure to the system, we can check if it holds that pressure. If the mmHg level drops, it indicates a problem.

So, all these measurements are like different languages to talk about pressure. They help us find problems in the EVAP system and make sure your car runs smoothly and doesn't pollute the environment with gasoline vapors.

---

How Does Vacuum Decay System Work

---

-10" and -11" H2O, represent vacuum limits for the Gross Leak test in a way that includes a minus (-) symbol. Let me explain how to read these values with an example:

Imagine you have a special device connected to your car's EVAP system to perform a Gross Leak test "weak vacuum test". This test is checking if there are any large leaks in the EVAP system. The device measures the vacuum level, which is how much pressure is lower than the atmospheric pressure (the pressure of the air around us).

• Atmospheric Pressure: The atmospheric pressure is the normal air pressure around us, which is about 14.7 pounds per square inch (PSI) or 29.9 inches of mercury (Hg) or 101.3 kilopascals (kPa) depending on the unit of measurement used.
• Minus Sign (-): When you see a minus (-) sign in front of the number, like in, -9" -10" or -11" H2O, it means that the pressure is lower than the atmospheric pressure. In other words, it's a vacuum.

Now, let's say you're performing the Gross Leak test, and the vacuum reading on the device shows:

• -10" H2O: This means that the pressure inside the EVAP system is 10 inches of water column lower than the atmospheric pressure. It indicates that the system is holding a vacuum of 10 inches H2O below normal atmospheric pressure. In this context, it's checking for leaks, and a lower value might indicate a problem.
• -11" H2O: Similarly, this means that the pressure inside the EVAP system is 11 inches of water column lower than the atmospheric pressure. It indicates a slightly stronger vacuum than -10" H2O, and it's also checking for leaks.

In both cases, a negative value indicates that the system is under a vacuum condition, and the test is looking for any significant changes in that vacuum level, which could be caused by leaks. If the vacuum level deviates significantly from these values, it might suggest that there's a gross leak in the EVAP system that needs attention.

---

---

Gauge and Absolute Vacuum Readings Explained 

---

How Does Vacuum Decay System Work:

Gauge Vacuum Reading:

Imagine you have a magical vacuum cleaner, and it can suck things up. The "gauge vacuum reading" is like measuring how much stuff the vacuum cleaner can suck up compared to the air pressure around us. It tells you how much lower the pressure inside the vacuum cleaner is compared to normal air pressure.

• Example: Let's say the normal air pressure around us is 14.7 pounds per square inch (PSI). If your vacuum cleaner can create a vacuum of -10 PSI, it means the pressure inside the vacuum cleaner is 10 PSI lower than the normal air pressure. So, it's like saying your vacuum cleaner can suck up things with 10 PSI less pressure.

Absolute Vacuum Reading:

Now, let's talk about "absolute vacuum reading." It's like measuring how much pressure there is inside the vacuum cleaner, no matter what the normal air pressure is. It gives you the full picture of how low the pressure goes.

• Example: If you have an "absolute vacuum reading" of 4.7 PSI, it means the pressure inside the vacuum cleaner is 4.7 PSI. It doesn't matter what the normal air pressure is; this reading tells you exactly how low the pressure goes inside the vacuum cleaner.

So, in a nutshell, "gauge vacuum reading" compares the vacuum to the normal air pressure, while "absolute vacuum reading" gives you the exact pressure inside, no matter what the normal air pressure is. Both are useful in different situations, depending on what you need to measure.

---

---

Small Leak Test

---

How Does Vacuum Decay System Work:

During the small leak test, the car's computer (PCM) is checking if there's just a little more pressure in the EVAP system than usual. If the pressure goes up too fast, it thinks there might be a small leak.

In a vacuum decay system, when we're doing the Gross Leak test, we have to let the vacuum out eventually. This test can be called an Excess Vacuum test, a system restored test, or a recovery test. To do this, the car's computer opens a special valve (vent solenoid) to let the air back in the EVAP system. While doing this, the computer is watching for the pressure to go up. If it doesn't go up much, it thinks something might be blocking the air in the EVAP system, like a clog, and it gets ready to show a warning code.

---

Purge Solenoid Test

---

---

How Does Vacuum Decay System Work:

A really important part of the EVAP system is something called the "purge solenoid." Imagine it as a special valve that can open and close when the car's computer (PCM) tells it to. The PCM uses the purge solenoid for different tasks, like checking for a big leak, or just normal cleaning of the system.

Now, there are two ways the PCM can make sure the purge solenoid is working properly:

1. First, it opens the purge solenoid and checks if the vacuum inside the system changes quickly. Then, it closes the solenoid and looks to see if the pressure inside the system goes up.
2. Second, it closes both the purge and vent solenoids and watches the pressure inside the system. If it suddenly turns into a vacuum (like a vacuum cleaner), it thinks there might be a problem with the purge solenoid.

So, the purge solenoid is like a gatekeeper, and the PCM is like a watchful guard making sure it opens and closes at the right times to keep the EVAP system working smoothly.

---

---

Smog Update Class Online Power Point Presentation 
Click Here for Access

---

Leak Detection Pump Operation

---

<