Fuel Pressure: Testing and Inspection

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).

Recommended special tools and equipment







- V.A.G 1318 pressure gauge
- VAG1318/7 adapter
- VAG1318/10 adapter
- V.A.G 1318/13 hose adapter

Without illustration:
- VAS5024A 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 (FP) In Fuel Tank, Check

Test sequence







- Remove fuse 28 for the Fuel Pump (FP) from fuse holder.







- Disconnect supply line -1- and catch escaping fuel using a rag.


WARNING: Fuel supply line is under pressure! Before loosening hose connections, place rags around the connection point. Then release pressure by carefully pulling on hose.







- Connect VAG1318 pressure gauge using adapters (1318/7, 1318/10 and 1318/13) to supply line and fuel distributor.
- Open shut-off valve of pressure gauge. The lever points in the direction of flow.
- Re-insert fuse 28 (fuel pump) into fuse holder.
- Start engine and let run at idle.
- Measure fuel pressure.
Specified value: approx. 3.5 bar positive pressure







- Disconnect vacuum hose from fuel pressure regulator (arrow). Fuel pressure should rise to
approx. 4.0 bar positive pressure rise.


NOTE: If fuel should escape at the vacuum connection of the pressure regulator, replace fuel pressure regulator, item 7 .


- Switch ignition off.

If specified value is not obtained:
- Check flow quantity of Fuel Pump (FP), Fuel Pump (FP).
Fuel Pump (FP) In Fuel Tank, Check
If specified value is obtained:
- 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 drop again:
- Test check-valve of Fuel Pump (FP), Fuel Pump (FP), checking. Fuel Pump (FP) In Fuel Tank, Check

If pressure does not drop:







- Open shut-off valve of pressure gauge (lever in direction of flow)
- 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, item 7 .
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness. Monitors, Trips, Drive Cycles and Readiness Codes

If pressure does drop again:
- Check whether line connections, O-rings in fuel distributor, and fuel injectors are properly sealed.
- Check pressure gauge for proper seal.

When removing pressure gauge after completed test:
- Remove fuse 28 again and place a rag around the adapter to be loosened and remove pressure gauge.
- Erase DTC memory of Engine Control Module (ECM), Diagnostic mode 4: Reset/erase diagnostic data.
- Generate readiness code. Monitors, Trips, Drive Cycles and Readiness Codes