2007 has Negative Pressure in the Fuel Tank

My C3 2007 has a problem in the fuel tank , when I open the fuel cap, the tank emerges a sound. I think this is due to the negative pressure on the tank, since the air enters to the tank when I open the cap.

I have read about the EVAP system, which purges the gases from the fuel tank. I think there is a problem in the EVAP system, but the diagnostic tool did not show any fault code.

what I need to know is how to find the defect in the EVAP system, (i.e. how to find the part which causes the problem).
or I want to know the place which allow the air to enter to the tank in order to balance the pressure inside the fuel tank.

Pleeeeeeeeeeeease help meeeee.

Thank You
Sincerely

Hi aghorab

This may help you
(Click to enlarge)

Thank You for your efforts, but I am not a specialist, I would like to ask you to describe how the air enters the fuel tank instead of the fuel itself in the normal situation.

I have a completely closed EVAP system, but the problem is I do not know how the air enters the fuel tank, can you show me on the diagram?

Thank You

I have found the following article which describes the EVAP system completely.

https://www.autozone.com/repairguides/Ra ... 3f802e2f27

look at this paragraph, is this correct for Citroen C3 ???

Fuel Tank Cap
The fuel tank is sealed with a pressure-vacuum relief filler cap. Under normal operating conditions, the filler cap operates as a check valve, allowing air to enter the tank to enable fuel flow. At the same time, it prevents fuel vapors from escaping through the cap to the atmosphere. These vapors are therefore forced into the EVAP canister.

The relief valves in the cap are a safety feature, preventing excessive pressure or vacuum in the fuel tank. If the cap is malfunctioning, and needs to be replaced, ensure that the replacement is the identical cap to ensure correct system operation.

Thanks

The Evaporative Emissions System (EVAP) allows fumes from the gas tank to enter the engine to be burned, rather than vented into the atmosphere as an emission. The purge valve solenoid is supplied switched battery voltage. The ECM controls the valve by operating the ground circuit, opening the purge valve at specific times allowing these gasses to enter the engine. The ECM monitors the ground circuit as well, watching for faults. When the purge solenoid isn't activated, the ECM should see a high voltage on the ground circuit. When the solenoid is activated, the ECM should see the ground voltage pulled low, close to zero. If the ECM doesn't see these expected voltages, or senses an open in the circuit, a code is set.

If there is no fault code, then the solenoid is probably working OK and there may be a mechanical rather than electrical problem.

aghorab wrote:look at this paragraph, is this correct for Citroen C3 ???

Yes, it looks similar. The paragraph above describes the Citroen system.

Until now no solutions found. Can anybody help me?.
By the way, I want a diagram for the fuek tank itself. does it contain a valve or a vent for the air.
Thank You