Without Tank Pressure Control Solenoid Vacuum (Tpc SV) Valve

Evaporative Emission (EVAP) Control System: Vehicles Without TPC SV Valve:

SYSTEM OVERVIEW
The basic Evaporative Emission (EVAP) control system used on all vehicles is the EVAP canister storage method. This method transfers fuel vapor from the fuel tank to an activated carbon (charcoal) device (EVAP canister) to hold the vapors when the vehicle is not operating. When the engine is running the fuel vapor is purged from the carbon element by intake air flow and consumed in the normal combustion process.

DESCRIPTION
An EVAP control system is used to prevent emission of fuel vapor.

The vapor generated in the fuel tank while driving, or with the engine at a stop, passes through a Tank Pressure Control (TPC) valve and enters the EVAP canister where charcoal absorbs and stores the fuel vapor.

The TPC valve is provided to keep pressure in the fuel tank constant. When the pressure in the fuel tank becomes positive and reaches its specified value, it opens the valve to let the vapor flow into the EVAP canister. When the pressure in the fuel tank becomes negative and reaches its specified value, it opens the valve to let the air flow into the fuel tank.

NOTE: In addtion to the Tank Pressure Control (TPC) valve described above, certain Geo Metro models are factory equipped with a Tank Pressure Control Solenoid Vacuum (TPC SV) valve. Vehicles equipped with a Tank Pressure Control Solenoid Vacuum valve have a three vapor hose fitting Tank Pressure Control valve and vehicles equipped without a Tank Pressure Control Solenoid Vacuum valve have a two vapor hose fitting Tank Pressure Control valve.

OPERATION
Only when the following conditions are satisfied, the Engine Control Module (ECM) opens the vacuum passage of the EVAP canister purge valve.

1. Engine Coolant Temperature (ECT) sensor is high (engine at operating temperature).
2. Engine speed is higher than specified.
3. Throttle valve opening not in the idle position.
4. Engine running within specified load.

As a result, fuel vapor in the EVAP canister is sucked into the intake manifold through the EVAP canister purge valve and purge hose. In this state, the EVAP canister is purged, or cleaned, by air drawn through the filter at the bottom of the EVAP canister.

RESULTS OF INCORRECT OPERATION
Poor Idle, Stalling And Driveability
Poor idle, stalling and poor driveability can be caused by:
^ Damaged EVAP canister.
^ Hoses split, cracked and/or not connected to the proper tubes.

Fuel Loss Or Fuel Vapor Odor
Evidence of fuel loss or fuel vapor odor can be caused by:
^ Liquid fuel leaking from fuel pipes.
^ Cracked or damaged EVAP canister.
^ Disconnected, misrouted, kinked, deteriorated or damaged vapor hoses.

Purge Valve Always Open
If the EVAP canister purge valve is open, the EVAP canister can purge to the intake manifold at all times. This can allow extra fuel at idle or during warm-up, which can cause rough or unstable idle, or too rich operation.

Purge Valve Always Closed
If the EVAP canister purge valve is closed, the EVAP canister can become overloaded resulting in fuel vapor odor.