So frustrating !!…CLICK…CLICK…CLICK. Just fill it already. Air-locked gas tanks are such a common problem, happened to my wife’s car only last summer. In the end, the solution was simple.
The most common cause of a gas tank that won’t fill quickly is a saturated charcoal canister. The canister is part of the EVAP system which is designed to trap harmful fuel vapors that contribute to smog.
In this post, you’ll know why the charcoal canister is causing slow refueling and what you can do to fix it.
EVAP Canister Saturated
The EVAP charcoal canister is tasked with storing environmentally harmful gas vapors from your gas tank. Under normal conditions, the canister stores vapors until the engine use them. As the canister ages, the pores charcoal becomes less efficient and vapors overcome the canister, filling it to capacity.
The canister simply becomes clogged or part clogged, this results in slow gas tank refueling. The tank is air locked, the displaced gas tank air can’t pass through the canister at the same rate fuel enters the tank.
This as you know results in the gas station pump cut off, kicking in repeatedly.
What Is The EVAP System?
The Evap system was introduced in the ’90s to help protect the environment from harmful gasoline vapors. As the sun rises it warms the air and that causes gas in a gas tank to evaporate. Pre 90’s cars have an open fuel system, meaning gas tank vapors were simply vented out through the gas cap and into the atmosphere to create smog.
The solution to this problem is the EVAP system. It seals the tank, stores the vapors, and reuses them as fuel when the engine is running.
The main components of the EVAP system include:
- Gas tank – sealed tank
- Gas cap – tasked with sealing the system
- Charcoal canister – Stores the vapors until used
- Vent valve – opens when commanded
- Purge solenoid – opens to allow vapors flow from canister to the combustion chamber
- Pressure sensor – monitors pressure loss inside the system
- Control module – manages the system and monitors and flags faults
What Is The ORVR System?
The ORVR (Onboard Refueling Vapor Recovery) is part of a vehicle’s EVAP system dedicated to capturing the fuel vapors when refueling. It works in conjunction with the EVAP system and the additional components of the ORVR system are internal to the gas tank.
The ORVR system includes a narrower gas tank refueling neck and a refueling valve at the base of the filler neck. The narrower neck and valve help prevent vapor release at the filler cap.
Wider tank to canister hose to allow vapors to move to the canister quickly, this makes for faster fuel filling without the dreaded gas pump cut out.
Where Is The EVAP Canister Located?
An EVAP canister is located on the underside of the car towards the rear close to the gas tank, usually. The canister may be obscured from view, as a protective cover is commonly fitted. If the canister is close to the exhaust system, it will be concealed behind a reflective heat shield.
In any event, the canister will likely have some form of protective shield obscuring it from view.
You’ll need to use an inspection lamp and look for tell tail pipework around the gas tank. Some cars mount the canister towards the front of the car, possibly behind a bumper or fender. A quick google of your model will show its location.
Can I Replace The EVAP Canister?
Replacing the canister on most vehicles is straightforward, no special tools or recalibration computers are needed. Often the greatest challenge is accessing. Large-size SUVs and trucks are among the easiest to replace as undercarriage space is plentiful.
Some vehicles may require other components removed just to access the canister. I would recommend replacing the vent valve in addition to the canister.
What Tool Do I Need To Replace EVAP Canister
- You’ll need a good hydraulic jack and axle stands. Never climb under a vehicle with just a jack, they can’t be trusted.
- Square nose pliers – removing hose clamps
- Socket set with extensions
- WD40 – helps with bolt thread corrosion
- Flexi hose clamp remover – great for removing difficult to access clamps
- Long flat screwdriver – prying off hoses
- Small pick – releasing electrical connector tabs
Check out my favorite tools on the Mechanics tools page.
Other Possible Causes For Slow Gas Tank Refueling
I’ve listed these as other possible causes because although the canister fix’s the majority of cases, I know it won’t be the answer for a small number of vehicles. So here’s a list of other possible, some I’ve experienced and some aren’t very likely at all but are still possible.
In no particular order:
- Faulty gas station pump – Had a customer who said it only happens at one particular gas station and at just one particular pump
- Faulty check valve
- Kink or dented filler tank neck – had a customer who jacked the vehicle while resting on the neck of the gas tank which resulted in restriction when refueling
- Pinched or twisted tank vent hose
- Faulty tank vapor valve
- Faulty tank fueling valve
How Much Does A Canister Cost?
You could replace your own canister for 100 – 300 dollars, having a shop do it might run to about 400 – 600 dollars plus they may charge extra for computer diagnosis.
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