Fuel Pressure Regulator and Residual Pressure, Checking

Fuel Pressure Regulator and Residual Pressure, Checking

Special tools, testers and auxiliary items required

• Pressure gauge for K-Jetronic (V.A.G 1318)

• Adapter set (V.A.G 1318/6+7) and (V.A.G 1318/7)

Test conditions

• Fuel Pump (FP) Relay OK.

• Fuel Pump (FP) OK.

• Fuel filter OK.

• Battery voltage at least 11 Volts.

• Parking brake engaged.

• Vehicles with automatic transmission: Selector lever in position P or N

• Electrical consumers switched off (Radiator fan must not run during test).

• A/C system switched off.

• Ignition switched off.

• The fuel pressure regulator controls the fuel pressure and is dependent on intake manifold pressure.

CAUTION!
Fuel system is under pressure! Before loosening hose connections or opening the test connection (for fuel pressure testing), place rags around the connection area. Then release pressure by carefully loosening the connection.

- Briefly open fuel filler cap (pressure release).

- Cover threaded connections that hold fuel pressure with a shop rag.

- Open fuel supply line threaded connection - arrow - and catch escaping fuel using a shop rag.





- Install fuel injection pressure gauge (V.A.G 1318) with adapters (V.A.G 1318/15) and (V.A.G 1318/7) between fuel supply line and fuel rail.





- Open shut-off valve of pressure gauge. The lever points in the direction of flow.

- Start the engine and run at idle speed.

- Measure fuel pressure.

Specification: approx. 3.5 bar positive pressure

- Disconnect vacuum hose - arrow - from fuel pressure regulator.





• If during the following pressure test, fuel drips from the vacuum connection of the fuel pressure regulator, replace fuel pressure regulator.

Fuel pressure must rise to approx. 4.0 bar positive pressure.

If specified value is not obtained:

- Replace fuel pressure regulator as a trial measure and repeat pressure test.

- If specified value is not obtained again, check Fuel Pump (FP) or supply line for damage (e.g. pinched areas) and replace if necessary.

If specification is obtained:

- Re-connect vacuum hose.

- Switch ignition off.

- Check for proper seal and residual pressure via pressure drop on pressure gauge.

After 10 minutes there must be a residual pressure of at least 2.5 bar.

The holding pressure drops below 2.5 bar:

- Start engine and let it idle approx. 4 minutes.

- Wait until pressure has risen, and then switch ignition off. Simultaneously close shut-off valve of fuel injection pressure gauge (V.A.G 1318) (lever perpendicular to direction of flow).





- Watch pressure drop on gauge.

If the pressure drops again, the following malfunctions are possible:

• Threaded connections of pressure gauge behind stopcock are not properly sealed.

• Fuel pressure regulator faulty

• Fuel injectors leaking

The following malfunctions are possible if the pressure does not drop:

• There is a leak in the threaded connection between the pressure gauge and the fuel supply line

• There is a leak at the supply line at fuel tank.

- There is a leak at the check valve in the Fuel Pump (FP). Check fuel pump

- After completing work, check fuel system for leaks => [ Fuel system, checking for proper seal ] Fuel System, Checking For Leaks.