Volkswagen Cars 2000-05

Fuel System Service Precautions

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The Digifant Motronic system is development of the electronically controlled Multiport Fuel Injection (MFI) system. This system is quite similar on all models, but there is one significant difference among the three engines, intake air flow is measured using one of two systems. The 1 .8L NA engine is equipped with a Vane Air Flow (VAF) sensor. This is a true mass air measurement system. The 1.8L SC and 2.5L NA engines use a Manifold Absolute Pressure (MAP) sensor.

Along with output from the Intake Air Temperature (IAT) sensor, the ECM can infer intake air flow by air temperature and pressure. This is a speed-density type control system. Using either measurement system, the ECM calculates the length of time the injectors should be opened, and with input from other sensors, also controls ignition timing.

The ECM is equipped with an adaptive learning program which allows it to learn and remember the normal operating range of the mixture control output signal. This allows the system to compensate for changes in altitude, slight vacuum leaks or other changes due to other things such as engine wear. Cold engine driveability and emissions are improved.

The ECM is also equipped with a fault memory. If the sensor signal or output solenoid feedback signal is outside preprogrammed parameters, the ECM will store a fault code representing the fault and sensor involved. The ECM will also illuminate the Malfunction Indicator Lamp (MIL) to inform the vehicle operator that the vehicle requires service. Some vehicles equipped with both the Digifant Motronic system and California specification emissions equipment also have the capability of flashing diagnostic codes.



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Fig. CIS-E fuel control system-Volkswagen CIS-E

Although Diesel fuel is not as flammable as gasoline, whenever working on or around diesel fuel or the fuel delivery system, heed the following precautions:



Do not allow fuel spray or fuel vapors to come into contact with a heating element or open flame. Do not smoke while working on the fuel system.
 
Always disconnect the negative battery cable unless the repair or test procedure requires that battery voltage be applied.
 
Always relieve the fuel system pressure prior to disconnecting any fitting or fuel line connection.
 
To control fuel spray when relieving system pressure, place a shop towel around the fitting prior to loosening to catch the spray. Ensure that all fuel spillage is quickly wiped up and that all fuel soaked rags are deposited into a proper fire safety container.
 
Always keep a dry chemical (Class B) fire extinguisher near the work area.
 
Always use a back-up wrench when loosening and tightening fuel line fittings.
 
Do not re-use fuel system gaskets and O-rings. Replace with new ones. Do not substitute fuel hose where fuel pipe is installed.
 



Do not disconnect the battery or the control unit before reading the fault codes. On the Motronic system, fault code memory is erased when power is interrupted.
 
Make sure the ignition switch is OFF before disconnecting any wiring.
 
Before removing or installing a control unit, disconnect the negative battery cable. The unit receives power through the main connector at all times and will be permanently damaged if improperly powered up or down.
 
Keep all parts and harnesses dry during service. Protect the control unit and all solid-state components from rough handling or extremes of temperature.
 

Safety is the most important factor when performing not only fuel system maintenance but any type of maintenance. Failure to conduct maintenance and repairs in a safe manner may result in serious personal injury or death. Maintenance and testing of the vehicle's fuel system components can be accomplished safely and effectively by adhering to the following rules and guidelines.



To avoid the possibility of fire and personal injury, always disconnect the negative battery cable unless the repair or test procedure requires that battery voltage be applied.
 
Always relieve the fuel system pressure prior to disconnecting any fuel system component (injector, fuel rail, pressure regulator, etc.), fitting or fuel line connection. Exercise extreme caution whenever relieving fuel system pressure to avoid exposing skin, face and eyes to fuel spray. Please be advised that fuel under pressure may penetrate the skin or any part of the body that it contacts.
 
Always place a shop towel or cloth around the fitting or connection prior to loosening to absorb any excess fuel due to spillage. Ensure that all fuel spillage (should it occur) is quickly removed from engine surfaces. Ensure that all fuel soaked cloths or towels are deposited into a suitable waste container.
 
Always keep a dry chemical (Class B) fire extinguisher near the work area.
 
Do not allow fuel spray or fuel vapors to come into contact with a spark or open flame.
 
Always use a back-up wrench when loosening and tightening fuel line connection fittings. This will prevent unnecessary stress and torsion to fuel line piping.
 
Always replace worn fuel fitting O-rings with new. Do not substitute fuel hose or equivalent where fuel pipe is installed.
 

Before servicing the vehicle, make sure to also refer to the precautions in the beginning of this section as well.

 
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