Fuel Pressure Regulator and Residual Pressure, Checking

Fuel Pressure Regulator And Residual Pressure, Checking

Function
The fuel pressure regulator controls the fuel pressure as a function of the Manifold Absolute Pressure (MAP).

The specified value for this test is dependent on the working pressure of the Fuel Pump (FP). This is about 3.0 bar positive pressure

Recommended special tools and equipment







- V.A.G 1318 pressure gauge
- VAG1318/10 adapter
- VAG1318/11 adapter
- VAG1318/16 hose adapter
- VAS5024 assembly tool for spring-type clamps

Test requirements
- Parking brake must be engaged or else daylight driving lights will be switched on.
- For vehicles with automatic transmission, selector lever must be in position -P- or -N-.
- Delivery quantity of Fuel Pump (FP) OK, Fuel Pump (FP), checking.
Fuel Pump, Checking

Test sequence

WARNING: Fuel system is under pressure! Before opening system, place rags around the connection point. Then release pressure by carefully loosening connection.

Vehicles with engine code AFP







- Disconnect fuel supply line -1- (black) from fuel distributor and catch escaping fuel using a rag.







- Connect pressure gauge V.A.G 1318 to adapter V.A.G 1318/10 at supply hose and to adapter V.A.G 1318/11 and hose adapter V.A.G 1318/16 at supply line.
- Open shut-off valve of pressure gauge. The lever points in the direction of flow (arrow).

Vehicles with engine code BDF







- Disconnect fuel supply line -1- (black) from fuel distributor and catch escaping fuel using a rag.







- Connect pressure gauge V.A.G 1318 to adapter V.A.G 1318/10 at supply hose -1- and to adapter V.A.G 1318/11 and hose adapter V.A.G 1318/16 at supply line.
- Open shut-off valve of pressure gauge. The lever points in the direction of flow (arrow).

Continuation for all vehicles
- Start engine and let run at idle.
- Measure fuel pressure.
Specified value: about 2.5 bar positive pressure

Vehicles with engine code AFP







- Disconnect vacuum hose from fuel pressure regulator (arrow). Fuel pressure should rise to about 3.0 bar positive pressure.

Vehicles with engine code BDF







- Disconnect vacuum hose from fuel pressure regulator (arrow). Fuel pressure should rise to about 3.0 bar positive pressure.

Continuation for all vehicles

NOTE: If fuel should escape at the vacuum connection of the pressure regulator, replace fuel pressure regulator:
- Vehicles with engine code AFP, item 15,
- Vehicles with engine code BDF, item 11.

- Switch ignition off.
- Now check for proper seal and residual pressure. Observe pressure drop on pressure gauge for this. After 10 minutes at least 2.0 bar positive pressure should still be present.

If residual pressure falls below 2 bar positive pressure:
- Start engine and let run at idle.







- Wait until pressure has risen, and then switch off ignition. Simultaneously close shut-off valve of pressure gauge (lever perpendicular to direction of flow -arrow-).
- Observe pressure drop on pressure gauge.

If pressure does not drop:
- Test check-valve of Fuel Pump (FP), Fuel Pump (FP), checking.
Fuel Pump, Checking

If pressure does drop again:
- Open stop valve of pressure gauge (lever in direction of flow -arrow-).
- Start engine and let run at idle.
- Wait until pressure has risen, and then switch off ignition. Simultaneously pinch return hose tightly together.

If pressure does not drop:
- Replace fuel pressure regulator:
- Vehicles with engine code AFP, item 15,
- Vehicles with engine code BDF, item 11.

If pressure does drop again:
- Check whether line connections, O-rings in fuel rail, and fuel injectors are properly sealed.
- Check whether pressure gauge is properly sealed.

NOTE: Before removing pressure gauge, put cleaning rags back around line connection which is to be disconnected.