Fuel Pressure: Testing and Inspection

Checking Fuel Pressure - Fuel System Without Return Line

WARNING: Observe the general safety instructions when working on the fuel system and when handling petrol and other fuels.

Attach or mount a warning notice on the vehicle in a clearly visible position -see Figure-.

Warning notice on 996 engine compartment lid










NOTE: The battery voltage may not fall below 12 volts during the fuel pressure check.

1. Check the battery charging condition e.g. using a voltmeter or the Porsche System Tester. The battery voltage may not fall below 12 volts during the check.

NOTE: Use the brass closure cap on the test connection of the fuel supply line only once as the sealing ring cannot be replaced. To avoid possible leaks, the cap must be replaced after removal.

2. Release the metal cap on the fuel collection pipe and screw it off by hand (a/f 13 mm).







3. Join the connecting cable No. 9559 using the special tool pressure gauge No. P 378a (union nut a/f 17). Screw the knurled union nuts of the connecting cable by hand onto the test connection of the fuel collection pipe -arrow-.

Proceed as follows when the engine is not running:

4. Connect Porsche System Tester PST 2 and switch on ignition.







5. Activate fuel pump relay using Porsche System Tester. To do this, select the line "drive links" in the DME control unit individual search and then select fuel pump relay. Activate by pressing "F8" -Figure-.

6. Read value on pressure gauge.







Target test values when engine not running: 3.8 ± 0.2 bar.

7. Switch off the fuel pump relay on the System Tester by pressing "F8".
8. Switch off ignition, pull off System Tester connecting lead in the vehicle and switch off System Tester.
9. When checking the engine at idle speed, connect the pressure gauge as described above and start the engine. Switch off the engine after reading the fuel pressure.

Target test values engine idling: 3.8 ± 0.2 bar.

10. Loosen the union nuts of the connecting cable No. 9559 for the special tool pressure gauge No. P 378a on the test connection and remove special tool. Collect emerging fuel, e.g. with a cloth.
11. Position new closure cap on test connection and tighten (a/f 13 mm).

Tightening torque of new brass closure cap: 2.5 (2.0) ± 0.5 Nm ( 0.5 ftlb.)