Rick's Free Auto Repair Advice

Why your car won’t start after pumping gas

An EVAP system failure is why your car won’t start after filling with gas

An Evaporative Emissions system problem is what causes your car to stall after filling with gas. The evaporative emissions system is designed to capture and store fuel vapors as you fill your tank, preventing them from polluting the air. Later, when you start your car, the vehicle computer will command a purge procedure to burn those vapors in your engine and get the system ready to store more vapor on your next fill-up. However, if the purge valve fails, and they fail quite often, the fuel vapors will flow directly into your engine while you fill with gas, flooding your engine. That’s why your car won’t start after filling with gas. I’ll show you how to get your car started and how to fix the problem.

The short version of how the EVAP system works

Your start filling your tank. The fuel vapor wants to vent out of the fill tube, but can’t because the nozzle is in the way

As you fill, the fuel vapor gets pushed into a canister filled with activated charcoal. The charcoal captures and holds the fuel vapors

You start the engine. The vehicle computer sees that you’ve filled with gas because it sees the new information on your fuel gauge. It commands a purge cycle.

A purge valve opens, allowed engine vacuum to suck the fuel vapors from the canister. Another valve opens, allowing fresh air into the charcoal canister to purge it of fuel.

The vehicle computer senses the fuel vapor being sucked into the engine and monitors it until the canister is completely purged. At that point, the engine is just sucking fresh air through the canister and into the engine. The computer senses that and closes the vent valve and then the purge valve.

Here’s what goes wrong with the evap system that causes your car to stall after filling with gas

The purge valve sticks open while you’re filling with gas, allow fuel vapors to flow into the engine instead of filling the charcoal canister with fuel vapor, the filling process pushes fuel vapor directly into the engine, flooding the engine and causing it not start and then stall.

The purge valve can stick open for several reasons:

a) The charcoal canister has failed and charcoal particles prevent the purge valve from closing
b) The purge solenoid wiring has an internal short to ground
c) The purge valve seat has debris and doesn’t seal properly
d) The purge valve has failed completely

How to test the purge valve

Use a multimeter to check for power and ground to the purge valve

Remove the hose from the charcoal canister and check forpurge valve the presence of charcoal particles in the hose and the purge valve. If you find particles, you must replace the canister, flush those and replace the purge valve.

If there are no particles, use a handheld vacuum pump to apply vacuum to the valve to see if the vacuum holds. Then apply power and ground to the valve to see if it opens/closes properly and still holds a vacuum. Replace the valve if it leaks or doesn’t operate.

Purge valve failure is common on all makes and models. It’s a fairly inexpensive part and you can replace it yourself.

How to start your car if it fails to start after filling it with gas

Since a failure in the evap system usually causes your engine to flood, do this:

Depress the gas pedal all the way to the floor and hold it there while you crank the engine. Depressing the pedal causes the computer to turn off the fuel injectors so no more fuel enters the engine. This allows fresh air to enter the cylinders and dry out the flooded fuel vapors.

After a few second of cranking like this, release the gas pedal and start normally.

©, 2022 Rick Muscoplat

 

Posted on by Rick Muscoplat



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