Fuel injection system adjustment - general information

Fuel system: multi-point injection models / Fuel injection system adjustment - general information

1 If a fault appears in the fuel injection system first ensure that all the system wiring connectors are securely connected and free of corrosion. Then ensure that the fault is not due to poor maintenance; ie, check that the air cleaner filter element is clean, the spark plugs are in good condition and correctly gapped, the cylinder compression pressures are correct, the ignition timing is correct and the engine breather hoses are clear and undamaged, referring to Chapter 1, Chapter 2A and Chapter 5B for further information.

2 If these checks fail to reveal the cause of the problem the vehicle should be taken to a suitably equipped VW dealer for testing. A diagnostic connector is incorporated in the engine management system wiring harness, into which a dedicated electronic test equipment can be plugged. The test equipment is capable of “interrogating” the engine management system ECU electronically and accessing its internal fault log. In this manner, faults can be pinpointed quickly and simply, even if their occurrence is intermittent. Testing all the system components individually in an attempt to locate the fault by elimination is a time consuming operation that is unlikely to be fruitful (particularly if the fault occurs dynamically) and carries a high risk of damage to the ECU’s internal components.

3 Experienced home mechanics equipped with an accurate tachometer and a carefullycalibrated exhaust gas analyser may be able to check the exhaust gas CO content and the engine idle speed; if these are found to be out of specification, then the vehicle must be taken to a suitably-equipped VW dealer for assessment. Idle speed and exhaust CO adjustment screws are provided (see illustrations), but adjustment will not be possible if the engine management system has detected and stored a fault in one of the fuelling or ignition system components. For this reason, all fault codes must be erased from the engine management system memory before the idle speed and exhaust CO settings can be checked and adjusted - this operation must be carried out by a WV dealer with the required test equipment.

10.3a Idle speed adjustment screw location

10.3b Exhaust CO adjustment screw location

10.3c Protective cap (arrowed) fitted to exhaust CO pre-catalyst sampling pipe (not fitted to later vehicles)

Caution: inaccurate CO adjustment may cause overfuelling and the risk of serious catalytic converter damage.