Why Does Car Sputter After Getting Gas?

Are you tired of coming to a stoplight and hearing your car sputter and cough after getting gas? It’s a common issue that many car owners experience, and it’s more than just a minor inconvenience.

In this article, we will discuss the various reasons why a car might sputter after getting or refilling gas, and how you can prevent it from happening again.

You can also read my guide on car won’t start after getting gas.

My Personal Experience With Car Sputtering Or Stalling After Getting Gas

Last year my brother’s old Toyota Camry started sputtering and stalling after he filled up at the gas station. I took a look under the hood and tested the fuel pressure – it was lower than specs.

Knowing the EVAP system can cause issues after refueling, I smoke tested the hoses. Sure enough, I found a cracked vapor hose going to the charcoal canister. After replacing the damaged section of hose, the car ran smoothly again.

It just took some EVAP troubleshooting know-how and a cheap hose replacement to get my brother back on the road.

What Exactly Is EVAP System?

The EVAP system, or Evaporative Emission Control System, is an important part of a vehicle’s emissions control system. This system is designed to capture and store fuel vapors that would otherwise escape into the atmosphere.

The EVAP system is made up of several components, including:

• Charcoal canister
• Purge valve
• Fuel tank pressure sensor
• Vent valve
• Gas cap of fuel tank 

The EVAP system works by routing fuel vapor from the fuel tank and fuel lines into an activated charcoal canister. This canister is then used to trap the fuel vapor and store it until the engine is running.

When the vehicle is running, the stored vapor is then drawn into the engine and burned off along with the other air-fuel mixture. 

The EVAP purge valve then opens, allowing the fuel vapors to be released into the engine.

The vent valve of EVAP system helps to prevent a vacuum from forming in the fuel tank. It allows fresh air to displace the fuel. The vent valve is opened all the time when the engine is running.

The only time the ECU closes the canister vent is when it self-tests EVAP system for leaks. You’ll almost always find this vent valve bolted directly to the canister.

The ECU (engine control unit) only opens the purge valve when it interprets that there is excess of fuel vapors in the fuel tank. This signal is sent by the fuel tank pressure sensor installed on the fuel tank.

Causes Of Car Sputtering After Getting Gas

Here are the causes of car sputtering after getting gas:

1. Gas Cap Is Not Properly Closed

After refueling your car, a loose gas cap is a common problem. Having a loose gas cap seal will cause an EVAP to malfunction. It usually does not cause performance issues in your vehicle but can trigger the check engine light if stays loose.

A check engine light is triggered because the ECU interprets that fuel vapors are leaking out of the fuel tank. This signal is sent by the fuel tank pressure sensor to the ECU.

However, if a gas cap stays loose for a long time, it can cause car to sputter. This is because gas caps are designed to seal the fuel tank, preventing fuel evaporation.

Furthermore, air from the atmosphere can suck into the fuel tank due to the vacuum inside the tank. This in turn affects the air-fuel ratio, leading to a loss of power and your car sputtering.

How to fix a loose gas cap?

Make sure that the seal of the gas cap is not cracked. You should tighten the gas gap until you hear 3 or 4 clicks.

Also, check if there are deposits of carbon or dirt around the seal of the gas cap or around the fuel filler neck of your vehicle in which a gas cap is tightened. 

Before replacing the gas cap, clean any dirt, debris, or rust from around the gas cap and filler neck.

Check that the gas cap seal is not cracked and lightly spray WD-40 on the seal to condition it, without allowing WD-40 to drip.

Also check for rust around the filler neck and lightly sand if needed. Finally, apply a thin coat of silicone grease to the filler neck ring to help the gas cap o-ring make a good seal and prevent leaks. This helps ensure proper fuel system operation.

You should also check if there is rust around the filler neck. If it is, lightly sand it with the sandpaper or steel brush.

2. Stuck EVAP Purge Valve

If your car engine sputters or stalls after filling up with gas, the cause could be a stuck EVAP purge valve. This valve releases fuel vapors from the gas tank into the engine to be burned off. It is electronically controlled to open at specific times.

If the EVAP valve gets stuck open, too many vapors enter the engine, causing an imbalanced air/fuel mixture.

This leads to a sputtering, stalling engine when you stop driving. The EVAP valve needs to open and close properly to prevent excess fuel vapors from building up. Getting the stuck valve repaired can fix the sputtering issue.

How to diagnose a bad EVAP purge valve?

The EVAP purge valve is located either next to the engine’s throttle body or near the fuel tank underneath the vehicle.

A stuck EVAP Purge Valve is often caused by dirt, debris, or other materials collecting inside the valve preventing it from opening and closing properly.

Issues with the EVAP valve’s solenoid can also lead to it getting stuck – the solenoid uses an electrical current to control the valve’s opening and closing. If the solenoid malfunctions, it will disrupt the valve’s normal operation.

Here are the following steps to test EVAP purge valve:

• Turn off the ignition switch.
• Locate purge valve with the help of EVAP system diagram in owner’s manual
• Remove the purge valve
• Take a vacuum pump tester and connect it with the port on the purge valve that goes to the intake manifold of the engine.
• If the valve is not holding the vacuum, it means it is faulty.

The following video will help you a lot:

3. Blocked Charcoal Canister

The charcoal canister contains activated charcoal that absorbs and retains fuel vapors from the fuel system. It is not designed to hold liquid gasoline, only vapors.

As the engine runs, excess fuel vapors are drawn into the charcoal canister and stored until needed. During refueling, released vapors are also stored until they can be routed back to the engine and burned.

Over time, the charcoal bed can become saturated with gas if too much vapor enters, like from overfilling. A saturated bed of charcoal canister cannot properly absorb gasoline vapors.

The canister must allow air flow so the tank can “breathe” as gasoline burns. If saturated, no air flows through, causing imbalanced pressure in the tank.

This leads to a sputtering, stalling engine because the proper vapor/air mix is disrupted. The engine needs the right balance of fuel vapors and air to run smoothly.

How to diagnose a bad charcoal canister?

Take out the charcoal canister, shake it and see if water, liquid fuel, or loose charcoal granules fall out. If yes, it means the charcoal canister is defective.

Using a flashlight, carefully inspect the exterior of the canister for any signs of damage, such as cracks or leaks. Additionally, inspect all hoses and connections of the charcoal canister for signs of wear, such as cracking or fraying.

You can also inspect the charcoal canister by blowing low-pressure compressed air into one port of charcoal canister, and see if air flows freely through the other port or not.

4. Damaged Vent Valve

The vent valve plays a crucial role in the EVAP system by allowing air to enter the system and preventing an overabundance of vacuum pressure inside the fuel tank.

When the vent valve is closed, it will prevent air from entering the EVAP system, leading to an overabundance of vacuum pressure, which can lead to fuel starvation of the fuel pump. As a result, this can cause the car to experience a sputtering engine due to a lack of proper fuel supply.

How to diagnose a bad vent valve?

To diagnose a canister vent valve, connect it to the vacuum pump just as we do to test the EVAP purge valve.

But for the canister vent valve, if the vacuum pump is not showing any vacuum, it means that the vent valve is healthy. If the pressure developed in the vent valve and it is being shown on the vacuum pump, it means that the vent valve is stuck closed.

For EVAP system to work properly, vent valve should remain open.

5. Kinks or Bends, Crack, Debris in the Fuel Vapor Hoses/Tubes

If your car engine sputters or stalls after filling up with gas, the issue may be with the fuel vapor hoses in the EVAP system. These hoses route fuel vapors from the gas tank to parts of the engine so the vapors can be burned.

If the hoses get damaged, kinked, or blocked, it can prevent proper fuel vapor flow. For example, a kinked hose restricts vapor flow, leading to an imbalanced air-fuel mixture.

This causes the engine to misfire and stall. In essence, with blocked hoses, the fuel tank can’t breathe properly. Checking and replacing damaged fuel vapor hoses can often fix sputtering and stalling problems after getting gas.

How to spot the bad fuel hoses?

To spot cracks in EVAP system hoses, you can use a UV light across the car’s underside, following the system’s path from the engine section to the rear fuel tank to inspect the EVAP system connections. Any smoke oozing from the system will lighten up in the ultraviolet light.

You might also need to perform a smoke test using a smoke machine to detect any leaks in EVAP hoses before proceeding further. For this, you can go to your nearby mechanic to have a professional smoke test done for the EVAP system.

To check the dirt or debris in the hoses, blow the air through them and see if there is some restriction that requires more force.

5. Bad Fuel Pump

A fuel pump is responsible for pumping fuel from the fuel tank to the engine, where it is then used to create the power needed to move the car.

As you can imagine, if the fuel pump isn’t working correctly, then your car won’t be able to get the fuel it needs to create power. 

The reason why a bad fuel pump can cause your car to sputter after it has been filled up with gas is because of something called “vacuum in the air space”.

When the fuel tank is unable to “breathe”, this vacuum will develop in the air space and this can cause the fuel pump to starve of fuel. 

How to spot a bad fuel pump?

Here is how to test fuel pump:

• Turn the ignition on
• Open the gas cap of the fuel tank
• If you do not hear the sound from the fuel tank, it could mean the fuel pump is not running
• Now, turn the ignition off
• If the fuel pump is running, you need to check fuel pressure using the fuel pump pressure test kit
• Locate the test port (Schrader valve) on the fuel line
• Fit down the hose of a pressure test kit on the test port
• If there is no fuel pressure on the test gauge, it means that the fuel pump needs to be replaced

6. Overfilling Of Fuel Tank

Overfilling your car’s fuel tank beyond capacity can seriously impact performance. The fuel system requires an air pocket to function properly (more on this in the later section). When overfilled, fuel enters components like the EVAP canister, sensors, and solenoids, instead of vapor.

This can make seals brittle, cause sputtering when starting, or even permanent damage. The EVAP system in particular helps store fuel vapors from the tank.

But overfilling causes it to fill with raw fuel, leading to stalling and sputtering. So it’s vital to avoid topping off the tank beyond the recommended full level.

How to fix?

Gas pumps use a mechanical linkage in the handle to sense the change in suction when gasoline in the tank rises high enough to block the hole.

When the hole is blocked, the higher-pressure air closes a valve and halts the flow of gasoline. This is why the nozzle makes a “clunk” sound when the fuel tank is full.

So, to avoid overfilling, you can keep track of how much fuel goes into the tank, examine the fuel gauge, and remove the nozzle when the safety clicks off at the station.

Moreover, by revving the engine high, you can burn the excessive fuel in the tank, so it’s not overfilled anymore.

Some Of The Common EVAP System OBD2 Codes

• P0440: EVAP System Malfunction
• P0441: EVAP System Incorrect Purge Flow
• P0442: EVAP System Leak Detected (Small)
• P0443: EVAP System Purge Control Valve Circuit
• P0444: EVAP System Purge Control Valve Circuit Open
• P0445: EVAP System Purge Control Valve Circuit Shorted
• P0446: EVAP System Vent Control Circuit Malfunction
• P0447: EVAP System Vent Control Circuit Open
• P0448: EVAP System Vent Control Circuit Shorted
• P0449: EVAP System Vent Valve/Solenoid Circuit Malfunction
• P0450: EVAP System Pressure Sensor Malfunction
• P0451: EVAP System Pressure Sensor Range/Performance
• P0452: EVAP System Pressure Sensor Low Input
• P0453: EVAP System Pressure Sensor High Input
• P0454: EVAP System Pressure Sensor Intermittent
• P0455: EVAP System Leak Detected (Gross Leak)
• P0456: EVAP System Leak Detected (Very Small)

You can use OBD2 scan tool to check if there is any trouble code.

Why Is EVAP System Introduced In Engines?

The EVAP system is designed to let your vehicle’s fuel tank breathe without releasing harmful fuel vapors into the air. Before the EVAP system, fuel tanks had vent holes to manage pressure but allowed fuel vapors to escape, which could create harmful gases.

The need for this breathing is to prevent a problem called cavitation, which can harm the fuel pump. When the fuel pump draws fuel from the tank, it creates a vacuum inside. If this vacuum isn’t balanced with air, it makes it hard for the pump to maintain fuel pressure, potentially starving the engine.

The EVAP system’s vent valve allows air to replace the fuel taken from the tank, keeping the fuel tank pressure steady and preventing engine starvation.

Final Thoughts

In summary, a car sputtering after getting gas can be incredibly frustrating, but is often caused by a simple issue with the EVAP system.

The most common causes are a loose gas cap, stuck purge valve, blocked charcoal canister, damaged vent valve, kinked hoses, bad fuel pump, or overfilling the tank.

To avoid this issue, be diligent about properly closing the gas cap, inspecting hoses for damage, not overfilling the tank, and addressing any OBD2 codes related to the EVAP system.

With proper maintenance and care taken when refueling, you can prevent those annoying sputters and keep your car running smoothly.

Some First Hand Experiences Shared By Users In Different Communities

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