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Checking injection quantity, leak tightness and spray pattern of injectors > < Checking idling speed

A3 Mk1

Motronic fuel injection and ignitionsystem (4-cyl. turbo)
Repairing the Motronic fuel injection system
Checking fuel pressure regulator and holding pressure

Test conditions

  • ● Check that fuel pump relay is OK .
  • ● Fuel pump OK.
  • ● Fuel filter OK.
  • ● Battery voltage OK.

Note:

The fuel pressure regulator regulates the fuel pressure according to the intake manifold pressure at the throttle valve unit.

Warning:
The fuel system is under pressure! Before opening the system place a cloth around the connection point. Then release pressure by carefully loosening the connection.
  • ‒ Briefly open the fuel tank filler cap (to release pressure).
  • ‒ Cover the pressurised screw connection with a cloth.
 
A24-0107
  • ‒ Pull the fuel supply hose (white marking) off the fuel supply pipe.
  • ‒ Connect the V.A.G 1318 pressure gauge to the fuel supply pipe using adapters 1318/8, 1318/9 and 1318/17.
  • ‒ → Open the cut-off valves in the pressure gauge. The lever points in the direction of flow.
  • ‒ Start the engine and run at idling speed.
  • ‒ Measure the fuel pressure.
  • Specified value: approx. 2.5 bar.
 
A24-0095
  • ‒ → Pull the vacuum hose off the fuel pressure regulator. The fuel pressure should increase to approx. 3.0 bar.
  • ‒ Switch the ignition off.
  • ‒ Check tightness and holding pressure by watching the gauge indicator fall.
  • ‒ After 10 minutes the remaining pressure should be at least 1.5 bar.

If the holding pressure drops below 1.5 bar:
 
A24-0106
  • ‒ Start the engine and run at idling speed.
  • ‒ → Allow the pressure to build up, then switch off the ignition. At the same time close the cut-off valve on the pressure gauge (valve handle at right angles to direction of flow).
  • ‒ Observe the pressure drop on the gauge.

If the pressure now does not drop:

  • ‒ Check the fuel pump non return valve.
 
A24-0107

However, if the pressure drops again:

  • ‒ → Open the cut-off valve on the V.A.G 1318 pressure gauge (valve handle points in direction of flow).
  • ‒ Start the engine and run at idling speed.
  • ‒ Allow the pressure to build up, then switch off the ignition. At the same time, pinch the return hose (with blue marking) firmly together.

If the pressure now does not drop:

  • ‒ Replace the fuel pressure regulator.

If the pressure drops again:

  • ‒ Check the pipe connections, O-rings on the fuel manifold and injectors for leaks.
  • ‒ Check the pressure gauge for leaks.

Note:

Before removing the pressure gauge, release the fuel pressure by opening the cut-off valve. Hold a container over the connection while doing so.

Checking injection quantity, leak tightness and spray pattern of injectors > < Checking idling speed