With Generic Scan Tool
Fuel Pressure Regulator And Residual Pressure, Checking
Recommended special tools and equipment
- Fuel Inj. Pressure Gauge Set V.A.G 1318 with adapters V.A.G 1318/6 and V.A.G 1318/7
Test requirements:
- Fuel Pump (FP) Relay OK. With Generic Scan Tool
- Delivery quantity of Fuel Pump (FP) OK. Fuel Pump (FP), Checking Delivery Quantity
- Fuel filter OK
- Parking brake engaged.
- Vehicles with automatic transmission: Selector lever in P or N.
- Electrical consumers switched off (radiator fan must NOT run during test).
- A/C switched off.
- Ignition switched off.
Procedure
- Remove rear engine cover (arrows).
Checking system pressure
CAUTION: Fuel system is under pressure. Before opening system, place rags around the connection. Then release pressure by carefully loosening connection.
- Open fuel filler flap briefly (pressure release).
- Connect e.g. V.A.G 1318 pressure gauge in fuel supply line using adapters 1318/6 and 1318/7.
- Disconnect vacuum hose from fuel pressure regulator to intake manifold at fuel pressure regulator and seal line.
NOTE: If fuel should escape at the vacuum connection of the pressure regulator during the following pressure test, replace pressure regulator.
- Start engine and let run at idle.
- Measure fuel pressure.
- Specified value: 3.8 ... 4.2 bar
- Switch ignition off.
If specified value is not obtained:
- Replace fuel pressure regulator as a test and repeat pressure test.
If specified value is again not obtained:
- Check Fuel Pump (FP) and supply line for damage (e.g. pinched areas), replace if necessary.
If the specified value is exceeded again:
- Check fuel return line for damage (e.g. pinched areas), replace if necessary.
NOTE: During the following test, the engine must not run for an unnecessarily long period of time with the vacuum hose removed. Otherwise, the higher fuel pressure can cause enrichment of the fuel to air ratio, which under some circumstances can cause the oxygen sensor control limits to be exceeded, causing a DTC to be stored.
- Start engine and let run at idle.
- Connect vacuum hose at fuel pressure regulator while observing pressure drop at pressure gauge.
- Fuel pressure must drop by approx. 0.5 bar when connecting the vacuum hose.
If the pressure change does not occur, the following tests must be performed:
- Check vacuum hose for tears and damage.
- Check vacuum hose at intake manifold for throughput by disconnecting hose from fuel pressure regulator and blowing into it.
- If no leaks can be detected and if the vacuum hose has throughput, replace the fuel pressure regulator.
Checking residual pressure
- Residual pressure 10 minutes after switching engine off (minimum pressure).
- Specified value with a cold engine: approx. 2.2 bar
- Specified value with the engine at operating temperature: approx. 3.0 bar
NOTE: Pressure increase for an engine at operating temperature caused by fuel expansion is normal.
- Start engine and let run at idle.
- Wait until pressure has risen, and then switch off ignition. Simultaneously close shut-off valve of VAG1318 pressure gauge (lever perpendicular to direction of flow -arrow-).
- Observe pressure drop on pressure gauge.
- Switch ignition off.
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 in the check valve in the Fuel Pump (FP).
NOTE: After the shut-off valve is closed, pressure gauge displays the pressure behind the shut-off valve "intake manifold side" (in direction of fuel injectors, fuel pressure regulator). If the pressure drops in front of the shut-off valve (in direction of fuel tank), the device cannot detect it.
The following malfunctions are possible if the pressure drops again:
- Fuel pressure regulator faulty
- Fuel injectors not properly sealed
- Threaded connections of pressure gauge behind shut-off valve are not properly sealed.
NOTE: To remove pressure gauge, close shut-off valve, loosen threaded connection at VAG1318/7 adapter and let excess fuel escape into catch reservoir by opening shut-off valve.
Final procedures
After repair work, the following work steps must be performed in the mentioned sequence:
1 - Check DTC memory, Diagnostic mode 3 - Check DTC memory. Diagnostic Mode 3: Check DTC Memory
2 - Erase DTC memory, diagnostic mode 4 - Reset/erase diagnostic data. Diagnostic Mode 4: Reset/Erase Diagnostic Data
3 - Generate readiness code. Readiness Code, Generating
- End diagnosis and switch ignition off.