Fuel Tank And Evaporative System Leak Detection

As part of the "Running Losses/CARB" emission requirements (TLEV compliancy), the introduction of yet another function was added to the ECM for vehicle evaporative emission control. Starting with the 96 328i and through the 97/98 model years on all E36 vehicles, the fuel tank and evaporative system had to be monitored for correct operation and leaks.

The evaporative system was redesigned from previous systems. Additional components were added to allow the monitoring of leaks and more precise control of fuel tank vapors. The components of the purge system include:
- Charcoal Canister with integral Shut Off Valve
- Evaporative Purge Valve
- Fuel Tank Pressure Sensor (transducer)
- Liquid/Vapor Separator
- Vehicle Fuel Tank

CHARCOAL CANISTER: The size of the Canister increased from 0.75 to a maximum of 3.0 liters depending on model.

The installed location of the canister is as follows:












E36 Sedan & Coupe models = in the trunk, under the spare tire.

Z3 1.9 & 2.8 =under vehicle on driver's side. (see next page).

318ti = in body shell cavity of left quarter panel, access by removing interior side panel as shown.

The increased volume of the canister provides containment of a larger volume of HC vapors without allowing any loss to the atmosphere.

Vapors that accumulate in the tank are allowed to pass from the tank through the liquid/vapor separator into the canister as in the past.

The purge line is routed from the canister, up to the engine compartment, through the purge valve and into the intake manifold.

A shut-off valve is installed on the intake or vent side of the charcoal canister. Operation of the valve is controlled by the ECM. When the shut-off valve and purge valve are closed, the entire fuel tank is sealed from the atmosphere. The shut-off valve is required to test the system for leaks.

PRESSURE TRANSDUCER: A fuel tank pressure transducer is required with this system to monitor captive system pressure during the leak detection test.












The signal from the fuel tank pressure sensor is an input to the Engine Control Module.

Depending on the input value from the sensor, the ECM can determine system operation and check for leaks.

The location of the pressure transducer is also model dependent.
- Sedan & Coupe models as shown above.
- 318ti, liquid vapor separator and pressure transducer located in the right quarter panel cavity (opposite side of canister location).
- On Z3 models the transducer is located on top of the fuel tank as shown in the illustration below.