Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Exhaust Emissions System - EVAP: Operation
The fuel vapor line, and on some models the filler neck, extends partially into fuel tank, causing an air pocket above fuel level in tank. As fuel expands, or when pressure in tank reaches 5 psi (.35 kg/cm2 ), valve in two-way check valve opens and allows fuel vapor to travel to charcoal canister.
On 1974 models, high ambient temperatures will also cause fuel in carburetor float chamber to expand. When the engine is not running, the carburetor float chamber control valve is open to the carbon canister and fuel vapors from the float chamber pass to the canister where they are absorbed by activated charcoal.
The charcoal canister removes gasoline vapors before venting to atmosphere. As fuel level drops, other valve in two-way check valve opens and air is drawn into fuel tank. Check ball allows fuel returning to tank to flow from pump to tank only.
Use the Manual With the Right Hardware
Pair factory procedures with proven DIY tools so the instructions are easier to execute.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.