Fuel Pressure: Testing and Inspection
Fuel Pressure Regulator and Residual Pressure, Checking
Special tools, testers and auxiliary items required
• Pressure tester (V.A.G 1318)
Conditions
• Fuel Pump (FP) relay OK.
• Fuel Pump (FP) OK
• Fuel filter OK.
• Battery voltage at least 11 Volts.
• Parking brake applied
• Vehicles with automatic transmission: Selector lever in position - P - or - N -.
• Electrical consumers switched off (radiator coolant fan must not run during test)
• Air conditioning switched off.
• Ignition switched off.
System pressure, checking
- Remove engine cover.
- Briefly open fuel filler cap (pressure release).
CAUTION!
• Work on the fuel system may only be performed when the engine is cold!
• 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.
- Open fuel supply line connection and absorb exiting fuel using a rag.
- Install pressure gauge (V.A.G 1318) to fuel supply line.
- Open shut-off tap on pressure gauge. Lever points in direction of flow.
- Start engine and run at idle speed.
- Measure fuel pressure.
Specification: approx. 4.0 bar positive pressure
- Switch ignition off.
- Check for proper seal and residual pressure by observing pressure drop on pressure gauge.
After 10 minutes there must be a residual pressure of at least 2.5 bar.
If the residual pressure drops below 2.5 bar:
- Start engine and run at idle speed.
- Wait until pressure has risen, then switch off ignition. At same time, close pressure gauge pressure gauge (V.A.G 1318) shut-off tap (lever at right angle to direction of flow) - arrow -.
- Observe pressure drop on gauge.
If the pressure now does not drop:
- Check pressure gauge for leaks.
- Check line connections and fuel injectors for leaks.
If the pressure drops again:
- Check pressure regulator in fuel filter.
Fuel pressure regulator, checking
- Remove covering from luggage compartment floor.
- Remove screws - arrows - from fuel flange cover and remove cover.
- Disconnect fuel return line - 1 - (press coupling button to release).
- Attach adapter - 2 - to disconnected fuel return line.
- Close off return line - 1 - with hose clamp (3094).
• The hose clamp (3094) must not come in contact with the fuel line connection or it may be damaged.
- Start engine and let it run at idle.
- Wait until pressure has risen and switch off ignition. Simultaneously close shut-off valve of pressure gauge (V.A.G 1318) (lever at right angle to direction of flow) - arrow -.
- Observe pressure drop on gauge.
If the pressure drops again:
- Replace Fuel Pump (FP). Return valve in FP is not sealing.
If the pressure now does not drop:
- Replace fuel filter with integrated fuel pressure regulator.
Assembly is in reverse order of disassembly, noting the following:
• Before removing the pressure gauge release the pressure by opening the shut-off valve. Also, use a container to catch any fuel that exits.
• To avoid damages to the catalytic converter, after work on the fuel lines or on the fuel filter, only start the engine when it is cold.
• The first engine start can take up to 15 seconds.
• Procedures upon completion of check.
Procedures upon completion of check
After repairing, perform the following steps in sequence:
1. Check Diagnostic Trouble Code (DTC) memory - Mode 3: Check DTC memory
2. If necessary, erase DTC memory - Mode 4: Reset/erase diagnostic data
3. Generate readiness code
- End diagnosis and switch ignition off.