Spluttering and Kangarooing is worrying especially when you’re on a long road trip. Anyway don’t panic, you are in the right place, this post covers all you need to know.
Car spluttering after a gas fill is commonly caused by a faulty EVAP system. A faulty stuck open EVAP purge valve will cause spluttering after a gas fill-up.
In this post, you’ll learn why your car splutters after filling with gas and what you can do to stop it from happening again.
What Is The EVAP System?
The EVAP (Evaporation) system is designed for the protection of the environment. In pre-EVAP vehicles, gas vapors in the fuel tank were exhausted from the atmosphere. This is harmful to the environment and as gas evaporates, it was wasteful too.
The solution is the sealed EVAP fuel system, first developed in the ’70s but not compulsory until the ’90s. It centers around the concept of a sealed gas tank. Fuel vapors are captured inside your gas tank and fed into air/fuel charge in a controlled manner.
How Does The EVAP Work
The system isn’t very complex but does require a couple of valves a sensor, a good gas cap, and some operator know-how to function correctly. The system comprises the following components:
- Gas Tank & Separator – Sealed tank with fluid separator
- Gas Cap – Maintains a sealed tank
- Tank pressure sensor – Helps controller make decisions and monitors leaks
- Vent valve/solenoid – Allows gas tank inhale
- Canister – Stores Vapors
- Purge valve/solenoid – releases vapors to engine
- Pipework – Transports vapors from tank to engine
- Controller (computer) – Manages the whole process
The controller is the brains of the operation, some EVAP systems have a separate computer to take care of the EVAP system and others are managed directly by the PCM.
The system does need careful management. Allowing uncontrolled vapors to enter the engine would cause a fuel-rich condition, poor running, and a ton of other issues. Fuel vapors are therefore carefully measured and released by the PCM (computer) into the engine’s intake manifold using a valve known as the purge valve.
The controller monitors gas tank pressure using a pressure sensor positioned inside the tank. It opens a vent valve to allow fresh air in when needed to displace the vapors consumed. The controller monitors tank pressure, even the slightest leak detected sets a MIL light.
The gas tank is sealed and employs a fuel separator to help prevent raw gas from making its way into the vapor lines and flooding the engine with gas.
The charcoal canister’s job is to collect, store vapors, and fed them to the engine once the engine is up to operating temperature.
Common Cause Of Spluttering After Gas Fill
The most likely cause of the spluttering is as you know, raw liquid gas inside the EVAP system. The system is designed to carry fuel vapors, not raw fuel. So what on earth is going on? The problem is most commonly caused by simply overfilling the gas tank. It’s an easy mistake to make, done it a ton of times.
When the gas pump at the station clicks, that means stop filling. Your gas tank needs an air pocket to operate correctly. Filling the gas tank to the very top (necking) causes the extra fuel to make its way through the pipework, flood the canister, and into the engine.
The problem resolves itself when you drive a few miles and the gas tank level drops. Try not filling the gas tank quite so full next time and note the difference.
Faulty Purge Valve
A faulty stuck open purge valve will cause problems. The valve or solenoid opens to allow vapors into the engine but only under controlled conditions. If the valve is open all the time the engine runs rich which can cause all kinds of problems.
Symptoms of faulty stuck open purge valve/solenoid, include:
- Stalling Hesitation
- Black smoke
- Hard starting
- Cuts out
- Won’t start
- Car jerks
- Car struggles
A faulty purge valve should cause a code and set in the car’s PCM and also set the MIL, but they don’t always. You can check the purge valve by either clamping off the feed line to the engine before filling with gas and checking the performance difference.
Alternatively, remove the purge valve and try blowing through it, it should be sealed. A normal default position is closed.
Loose Gas Cap
A loose gas cap is also a common issue after filling up but generally only causes a MIL light with no real performance issues. Simply turning the cap until it clicks solves the problem. The MIL light will turn itself off when it confirms the cap is no longer loose.
Common EVAP System Faults
Here’s a list of all the most common EVAP faults, and the fix. Common fault codes – P0440 leak code; P0443 purge valve fault. All will cause the engine light to come on (MIL on):
- Gas cap loose – (P0440) Tighten the cap
- Gas cap seal worn – Replace the cap
- Faulty Purge valve – (P0443) Replace the valve
- Blocked canister – Replace
- System leak – (P0442) Use smoke machine to detect leak and repair
- Vent valve faulty – Replace
- Pressure sensor faulty – Replace
Does gas cap check engine light on? The gas cap is loose or the gas cap seal is worn. Tighten the cap and the system will reset automatically if all is in order.
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