EVAP system

The Evaporative Emission Control System (EVAP) is used to prevent gasoline vapors from escaping into the atmosphere from the fuel tank and fuel system at all times.

A typical system consists of the fuel tank, an EVAP vapor storage canister full of charcoal, valves, hoses and a sealed fuel tank gas cap. The EVAP system is designed to stop fuel system fumes from leaking directly into the atmosphere. Vent lines from the fuel tank pass vapors to the vapor canister, where they are trapped and stored until the engine is started. When the engine is warm and the vehicle is going down the road, the PCM then opens a purge valve allowing the vapors to be drawn from the storage canister into the intake manifold. The fuel vapors are then burned in the engine along with the air/fuel mixture.

Fuel evaporation control system function

Shown on engine 119 75 - Fuel tank 77 - Activated charcoal canister N3/10 - ME control unit Y58/1 - Purge control valve a - Pressurization line

Shown on ENGINE 120 75 - Fuel tank 77 - Activated charcoal canister 93 - Expansion reservoir (only with optional ski bag) M16/3 - Right EA/CC/ISC actuator Position on left of engine M16/4 - Left EA/CC/ISC actuator Position on right of engine N3/11 - Left ME-SFI [ME] control unit N3/12 - Right ME-SFI [ME] control unit Y58/2 - Switchover valve Left regeneration Y58/3 - Switchover valve Right regeneration a - Pressurization line

The fuel evaporation control system prevents fuel vapors escaping to atmosphere. This is done by storing the fuel vapors temporarily in the activated charcoal canister.

When the engine is running, the fuel vapors stored in the activated charcoal canister are drawn off through the purge control valve and combusted in the engine. The activated charcoal canister is purged (re-generated) at:

• Coolant temperature > 70 °C
• Blocking time after engine start elapsed, approx. 2 minutes
• Engine not in deceleration mode

The purge quantity is controlled by the ME-SFI control unit operating the purge control valve. The purge quantity is determined by constantly opening and closing the purge control valve for on and off periods of various lengths.

The idle speed control prevents changes in engine speed resulting from purging. A richer or leaner fuel-air mixture is produced in line with the charge of the activated charcoal canister with fuel vapors.

Air admission to fuel tank. Air is admitted through the activated charcoal canister. This is done through the activated charcoal canister, whereby air is drawn out of the vent/breather line or fuel vapors are drawn from the activated charcoal canister into the fuel tank.

Air release from fuel tank. The fuel tank is vented through the activated charcoal canister. The fuel vapors flow to the activated charcoal canister, where they are stored or drawn into the intake manifold in case of simultaneous regeneration.

Vent valve. On vehicles fitted with a vent valve the fuel tank is vented from a pressure of 30 to 50 mbar, and air admitted at a vacuum of 1 to 16 mbar. In addition, this prevents overfilling the fuel tank.

USA as of MY 98. During refueling the fuel vapors are collected at the filler neck and passed to the activated charcoal filter (ORVR = Onboard Refueling Vapor Recovery). Large activated charcoal canister.

Engines with charging (compressor or turbocharger). A check valve in the purge line prevents the boost pressure building up toward the activated charcoal canister.

Model 215 from chassis no. A046659 (approx. 23.3.05), without USA and model 220 from chassis no. 469233 (ca. 23.3.05), without USA with ski bag (Code 282) or cooling compartment in rear backrest (Code 308) or with retrofitted additional vent valve (76/1):

75 - Fuel tank 76 - Vent valve (standard) 76/1 - Vent valve (additional from series production breakpoint or retrofitted) 77 - Activated charcoal canister N3/10 - ME-SFI [ME] control unit Y58/1 - Purge control valve A - to intake manifold B - Air admission C - Line to fuel tank D - Line to purge control valve

The additional vent valve (76/1) prevents the vacuum from the intake manifold passing over the activated charcoal canister through to the fuel tank for enabled purging. For this purpose, the valve closes as soon as a membrane is pressurized with vacuum pressure from the activated charcoal canister. If excess pressure or vacuum pressure affects the other valve connection, it opens immediately. This means aeration/venting of the fuel tank is then possible in an unlimited fashion via the standard vent valve (76).

Pay attention to the installation position of the vent valve (76/1). Check aeration at the activated charcoal canister for contamination (e.g. dust, spider's webs).

Fuel tank ventilation system

Shown on model 210.0 without ski bag (through-loading feature):

Function. The ventilation system consists of a central pipe (42/2) with an interruption vessel (42/1) at each end. The interruption vessels prevent fuel escaping along the vent line. The vent line (91) runs from the central pipe to the vent hose (93). On vehicles fitted with a gasoline engine, the vent hose (93) runs to the activated charcoal canister. As of approx. 7/98 a vent valve is integrated in the vent line to the activated charcoal canister (without USA).

Fuel filler neck with cap (USA)

Shown on Model 210 sedan: 45 - Filler neck 45/1 - Flap (operated from nozzle) 45/2 - Float 45/3 - Corrugated tube 45/4 - Pressure relief valve (in top insert integrated at corrugated tube, release pressure approx. 60 - 90 mbar) 45/5 - Flap (operated from float) 45/6 - Bottom inser 45/7 - Connection for collecting fuel vapors when refueling 45/8 - Top insert 84 - Closing cover

The fuel filler neck (45) runs through the right, rear wheelhousing to the fuel tank. It has an inserted insert and connection for collecting fuel vapors when refueling. The insert which is inserted in the filler neck prevents, that fuel flows to the activated charcoal canister due to inappropriate refueling.

The fuel vapors in the filler neck are diverted several times in order to separate the gases from the fuel. The connection to the activated charcoal canister is shut off by a flap (45/1) when driving by means of the top insert. It is opened by the gasoline pump nozzle when refueling. When the fuel tank is full, a float closes a flap at the bottom insert. The filler neck is filled rapidly and the gasoline pump nozzle switches off.

Purge control valve actuation function

Shown on engine 119 in model 129, 140: 75 - Fuel tank 77 - Activated charcoal canister B2/5 - Hot film mass air flow sensor B11/4 - Coolant temperature sensor B17 - Intake air temperature sensor L5 - Crankshaft position sensor M16/1 - Electronic accelerator (EA)/ cruise control (CC)/ idle speed control (ISC) actuator N3/10 - ME-SFI control unit N16/1 - Base module Y58/1 - Purge control valve

For controlling the purge quantity the purge control valve is actuated at the ground side by the ME-SFI control unit by means of a pulse width-modulated signal. The purge quantity is determined by constantly opening and closing the purge control valve for on and off periods of various lengths.

The frequency of the pulse width modulation signal is selected from a speed-dependent characteristic in such a way, that all cylinders are uniformly supplied with fuel vapors.

The purge control valve is actuated when the engine is at operating temperature, but not in the deceleration mode.

The following information is processed in the ME-SFI control unit:

• Engine speed
• Air mass (boost pressure in supercharged engines)
• Coolant temperature
• Intake air temperature (charge air temperature in supercharged engines)

Activated charcoal canister

1 - Housing 2 - Activated charcoal granulate 3 - Vent line of the fuel tank 4 - Vent line of the activated charcoal canister (USA with activated charcoal canister shutoff valve) 5 - Purge line (to the purge control valve)

The task of the activated charcoal canister is ventilation and deventilation of the fuel tank and storing the fuel vapors temporarily for subsequent purging.

The hausing of the activated charcoal canister is filled with activated charcoal granulate, divided into different chambers by intermediate walls in order to achieve optimal flow through the activated charcoal. USA with ORVR: Quantities of around 2.7 to 3.5 l.

The fuel vapors released from the fuel tank (USA with ORVR or when refueling) are bonded to the activated charcoal. When purging is activated, they are drawn in by the engine and combusted. The activated charcoal is completely regenerated in the ideal case. The ventilation and deventilation of the fuel tank takes place over the activated charcoal canister.

The activated charcoal canister is located at the rear in the rear left wheelhouse.

77 - Activated charcoal canister A - Activated charcoal canister line to purge control valve D - Activated charcoal canister line to fuel tank

USA with ORVR: 77 - Activated charcoal canister Y58/4 - Activated charcoal canister shutoff valve

Activated charcoal canister shutoff valve (USA)

Shown in the design of model 210: 77 - Activated charcoal canister Y58/4 - Activated charcoal canister shutoff valve A - Ventilation via the shutoff valve B - Ventilation via the safety valve

The task of the activated charcoal canister shutoff valve is to close the ventilation of the activated charcoal canister for a leakage test of the fuel system.

The shutoff valve contains a solenoid which closes the valve when energizing. Additionally a mechanical safety valve is installed.

The shutoff valve is located on the top at the vent connection of the activated charcoal canister.

77 - Activated charcoal canister 80/7 - Plastic nuts 82/4 - Hose clamp Y58/4 - Activated charcoal canister shutoff valve

Purge control valve

Y58/1 - Purge control valve Y58/2 - Left purge control valve (engine 120) Y58/3 - Right purge control valve (engine 120) B - to activated charcoal canister C - to engine (identification "engine inspection")

The task of the purge control valve is opening and closing the connecting line between the activated charcoal canister and the intake manifold.

The purge control valve is an electric switchover valve with two line terminals and one 2-pin plug connection.

Y58/1 - Purge control valve A - from activated charcoal canister B - to intake manifold

The purge control valve (Y58/1) is actuated by the ME control unit by means of a PWM signal (ground side) in line with the operating condition of the engine. If purging is actuated, the passage from the activated charcoal canister (a) to the intake manifold (b) is opened and closed.

The voltage supply to the purge control valve is performed by terminal 87.

The purge control valve is located in the engine compartment at the left wheelhouse.

Y58/1 - Purge control valve

Vent valve

Shows model 220: 75 - Fuel tank 76 - Vent valve 90/11 - Fuel return line 90/12 - Fuel pressure line D - Vent line to activated charcoal canister

The task of the vent valve is the air admission and ventilation of fuel tank and prevention of overfilling. The vent valve (76) is mounted under the fuel tank in the vent line.

1 - Compression spring 2 - Valve housing 3 - Spring cup 4 - Bleed valve 5 - Valve plate 6 - Air admission valve 7 - Connection 76 - Vent valve A - Connection to activated charcoal canister B - Connection to fuel tank

Fuel tank ventilation. The ventilation valve (4) opens at an overpressure of around 30 to 50 mbar. The fuel vapors flow to the activated charcoal canister.

Fuel tank aeration. The air admission valve (6) opens at a vacuum of around 1 to 16 mbar in the fuel tank. Air or fuel vapors are drawn in through the activated charcoal canister.

Refueling. The opening pressure of the vent valve (4) of approx. 30 up to 50 mbar is not achieved if the fuel tank cap is removed. The vent line to the activated charcoal canister remains closed off. This switches off the nozzle more rapidly.

Parts

EVAP system related parts in EPC

Connection diagram for evaporative emission control system (M113)

Shown on engine 113 from 09/97 in model 210 17 - Fuel distributor 19 - Intake manifold 75 - Fuel tank 77 - Activated charcoal canister A - Activated charcoal canister line to purge control valve B - Purge control valve line for to intake manifold C - Vent line from activated charcoal canister to fuel tank D - Line for activated charcoal canister vent valve to fuel tank M3 - Fuel pump M16/1 - EA/CC/ISC [EFP/TPM/LLR] actuator (only models 129, 210) Y58/1 - Purge control valve Y62 - Fuel injection valves

(Note: the fuel filter is incorrectly depicted in this picture. Refer to the M112 picture below.)

Connection diagram for evaporative emission control system (M112)

Shown on engine 112 from 09/97 in model 210 17 - Fuel distributor 19 - Intake manifold 45 - Filler neck (with connection for on-board refueling vapor recovery ORVR) 55/1 - Fuel filter 75 - Fuel tank 77 - Activated charcoal canister M3 - Fuel pump M16/1 - EA/CC/ISC [EFP/TPM/LLR] actuator (only models 129, 210) Y58/1 - Purge control valve Y62 - Fuel injection valves A - Activated charcoal canister line to purge control valve B - Purge control valve line for to intake manifold C - Activated charcoal canister line to fuel tank D - Fuel tank line to activated charcoal canister E - Fuel filter degassing line to fuel tank F - Fuel filter fuel tank fuel return line to fuel tank

Remove/install activated charcoal canister

Shown on MODEL 220 77 - Activated charcoal canister A - Activated charcoal canister purge control valve line D - Vent valve line from activated charcoal canister to fuel tank

1. Raise vehicle.
2. Remove rear left wheelhousing liner
3. Detach activated charcoal canister - purge control valve line (A) and vent valve line - activated charcoal canister to fuel tank (D) at activated charcoal canister (77)
4. Remove activated charcoal canister (77). Lift up and out.
5. Install in the reverse order