See Figure 1
The evaporative emission control system consists of the fuel tank, expansion tank, carbon canister, fuel filler cap, solenoid-activated purge valve and connecting lines or hoses. The filler cap is a check valve that allows air into the tank but does not allow vapors out.
With the engine off, gasoline vapors are collected in the expansion tank, while liquid fuel is condensed and flows back to the fuel tank. Vapors are routed to the carbon canister where they are stored until the engine is started. They are drawn from the carbon canister by engine vacuum. When the ignition switch is ON , the purge valve receives 12 volts from the main DME relay. The control unit will complete the circuit by providing ground and the valve will close.
As the appropriate conditions are met, the control unit will provide or deny ground to cycle the valve open and closed. When the valve is open, manifold vacuum pulls fresh air into the canister and the air/vapor mixture is drawn into the intake manifold or throttle body. This air flow is not measured by the air mass meter but the duty cycle of the valve is accounted for by the control unit. If the hose is leaking between the valve the intake manifold, there will be a vacuum leak.
The purge valve can also be referred to as the venting valve. The carbon canister is also known as a charcoal canister. These terms can be used interchangeably.
On vehicles equipped with the M20 engine, the molded hose that connects the purge valve to the intake manifold can crack and cause a rough idle. Check the small end of the hose where it is connected to the intake manifold for damage caused by the clamp and replace if necessary.Testing
SOLENOID PURGE VALVE
See Figure 2
- Unplug the purge valve electrical connector. The valve located under the air intake hose or intake manifold. It has 1 electrical connector and 2 vacuum lines, 1 leading to manifold vacuum and the other to the carbon canister.
- The coil resistance should be 25-65 ohms.
- Attach a hand vacuum pump and gauge to the intake manifold side of the valve. Supply 12 volts to the valve to hold the valve closed. Apply 15-21 in. Hg. (500-700 mbar) of vacuum to the valve.
- Wait 20 seconds and check the gauge to determine if a vacuum has been lost. If a drop of more than 1.5 in. Hg. (50 mbar) occurs, the valve must be replaced.
- If the valve is good, but the system is still suspect, reinstall the valve, then start and warm the engine to normal operating temperature.
- When the engine has reached normal operating temperature and the system should be normally operating, carefully unplug the electrical connector from the valve. Connect a voltmeter to the connector terminals; the meter should cycle between 0-12 volts as the control unit supplies and denies ground.
- If there is no voltage, check the wiring between the valve, DME relay and the control unit for continuity. If the wiring is good, the control unit is faulty.
- If the voltage is ON continuously, turn the ignition switch OFF and check for a short in the wiring or short to ground.
REMOVAL & INSTALLATION
Solenoid Purge Valve
- Disconnect the negative battery cable.
- For the E36 3 Series with M50 engine, open the hose clamps, then remove the intake bellows and air mass sensor to provide access.
- Lift off or compress the retainer, then unplug the valve electrical connector.
- Except for the E36 3 Series with M50 engine, loosen and remove the retaining bolt.
- Disconnect the hoses from the valve, then remove the valve from the vehicle.
- Install the valve and connect the vent hoses.
- If removed, install the retaining bolt.
- Install the electrical connector and retainer to the valve.
- If removed, install the air mass sensor and intake bellows, then tighten the hose clamps.
- Connect the negative battery cable.
See Figures 3 and 4
- If the venting hose is not a slide-on type connection, open the connecting nipple using tool 16 1 040 or equivalent, then pull off the tank venting pipe.
- Remove the hose from the canister.
- Unclip the filter vent.
- Remove the mounting screws and remove the canister from the vehicle.
- Position the canister, then install and tighten the mounting screws.
- Position the filter vent in the clip.
- Install the hose to the canister, then install the tank venting pipe. The hose will push on and clip into place.
See Figure 5
- Remove the right rear wheel. Remove the wheel well rear trim.
- Disconnect the hoses from the tank.
- Remove the mounting bolts and remove the expansion tank.
- Install the expansion tank and connect the hoses.
- Replace the wheel well trim and the wheel.