Pressure regulator
Pressure measurements require an appropriate pressure gauge (V.A.G. 1318) with stopcock and adapter. In idle mode, the fuel supply pressure should be approximately 2.5 bar, with the vacuum hose removed from the pressure regulator, it should rise to 3 bar.
Throttle Potentiometer Check
Disconnect the plug of the throttle valve potentiometer.
Connect an ohmmeter to pins 1 and 2.
Move the throttle while keeping an eye on the ohmmeter. The resistance should change evenly.
Checking injection nozzles
For electrical checks, you will need an LED voltmeter.
Checking the power supply: Remove the plugs on the injection nozzles one by one.
Connect a voltmeter to the contacts of the removed plug.
Have an assistant start the engine.
The LEDs should flicker, otherwise there is a defect in the wiring to the injectors or the control unit itself is faulty.
Checking the injectors: remove all plugs on the injection nozzles.
Connect an ohmmeter to both plug contacts of the first injection nozzle.
Standard indicator: 15-20 Ohm.
Repeat test on other injectors.
More detailed check (jet type/tightness)
Remove the injection nozzles together with the distributor pipe - description of work see later in this chapter.
However, the wire ends must remain on and the fuel lines connected.
On the left in the pipe of the cooling system, remove the plugs of the starting valve and the temperature sensor.
Direct injection nozzles into four measuring containers.
Left: injection nozzles (arrow) are located on the right side in the direction of travel of the cylinder head in the intake manifold.
Right: In the illustration, the connecting plug has been removed (1) with injection nozzle (2). With an LED voltmeter, you can check whether the power supply to the injection nozzles is OK.
Now the assistant should rotate the starter within a few seconds: the injection jet should be the same for all four nozzles. In this case, the jet view is fine.
Remove central plug for injection nozzles in cable duct.
Turn off the ignition and turn it on for 5 seconds: no more than two drops should come out of each nozzle. In this case, the tightness of the nozzles is in order.
Checking temperature sensors
Intake air temperature sensor: Disconnect the 4-pin connector at the top of the air mass meter.
Connect an ohmmeter to both external plug contacts.
Coolant temperature sensor: Disconnect the blue plug from the sensor in the coolant filler neck.
Connect an ohmmeter to the plug contacts of the sensor.
Both sensors: read resistance readings.
According to the diagram, check if the data for the resistance of the sensors is found (air and coolant temperature) at the time of measurement within the curve.
If so, then the sensors are OK.
Start valve
Disconnect plugs from all injection nozzles.
Power supply: remove the wire end on the start valve.
Connect the LED voltmeter with auxiliary wiring to the plug.
Disconnect plug from coolant temperature sensor.
The assistant should crank the engine with the starter, while the LED should flash for 1-4 seconds.
If this does not happen, then the wiring is interrupted, or the control unit of the Digifant injection system is faulty.
Operation check: The injector plugs are still disconnected.
Unscrew the start valve, the lugs of the wires and the fuel lines remain connected.
Disconnect plug from coolant temperature sensor.
Direct the starting valve into some container.
Have an assistant turn the engine over with the starter.
Within 1-4 seconds, the valve should inject gasoline in a uniform jet.
Wipe the valve clean to check the tightness,
Gasoline should not come out of it for a minute, the starting valve should also not give the impression of being wet from fuel.
Lambda probe
This check requires a CO meter, so you may have to visit a workshop. For proper control, the exhaust system must be in good condition, and the lambda probe must be powered (are the fuses ok?).
Warm up the engine.
Connect a device for measuring CO content.
Start the engine and let it idle for at least 2 minutes.
Increase the speed to 2000 rpm.
Write down the content of the CO.
On the throttle body, remove the pressure regulator vacuum hose and close the tube with your finger.
The CO content should rise for a short time and then fall again to the already measured value
If the CO value does not change, disconnect the plug connection to the lambda probe.
This chart is for the coolant temperature sensor («1» in the illustration on the left). This indicates what resistance should be in the sensor at a certain coolant temperature. Position «2» stands for coolant temperature sensor and temperature readings (see additional chapter «Tools and devices»).
Stop valve (arrow), visible in the air passage of the air mass meter, should move slightly. The electrical check of the air mass meter is carried out by connecting contacts, which in this illustration are visible at the top of the air mass meter housing.
Wire the contact on the plug (to the control unit) alternately with the positive and negative battery terminals.
If during this check the CO indicator changes, then the lambda probe is faulty.
If the value of the CO content remains unchanged, then you need to check the wiring to the control unit.
If there are no faults here, then the control unit is faulty.
Air mass meter
Remove the wire end on the air mass meter.
The numbering of the contact tongues when viewed from above goes from left to right from 1 to 4.
Intake air temperature sensor: on pins 1 and 4, check that the sensors are working as described in paragraph «Checking temperature sensors».
Potentiometer: Connect an ohmmeter between middle pins 2 and 3.
Move the shut-off valve while observing the ohmmeter.
The resistance must change.
Connect an ohmmeter between pins 3 and 4.
The resistance value must be between 0.5 and 1 kΩ (constant).
If you get different readings during the measurement, you need to replace the air mass meter.
Idle stabilization
Turn on the ignition - the valve should make a slight humming sound. In addition, you can feel its slight vibration.
Otherwise, check the fuses.
If all fuses are OK, disconnect the plug on the idle speed control valve. With a diode test lamp, check the presence of power in the plug on the contact of the black-blue wire (with the ignition on). To do this, connect the other contact of the diode control lamp to «mass».
If the light flashes, then the power supply to the valve is in order. Therefore, you need to check the valve itself:
Connect an ohmmeter and check the resistance at the plug contacts of the valve.
If the valve is working, the resistance indicator should be 2-10 ohms.
Left: plug connection on the rear wall of the engine compartment. Designation:
1 - plug connection of the knock sensor;
2 - plug connection for heating the lambda probe;
3 - plug connection of the lambda probe signal.
Right: starting fuel valve (arrow) located in an easily accessible place on the rear right side of the intake manifold.
In the illustration, the plug of the idle control valve is removed (arrow), in order to check the valve and wiring to it (see text).
If the specification is not reached, replace the valve.
With the correct resistance, the cause of the malfunction should be sought in a broken wiring or a defect in the Digifant injection system control unit.
To check the control, the control current is measured. To do this, the workshop uses a device to interrogate the memory of the VAG 1551 fault drive, measurement by improvised means does not make sense.
Visitor comments