Differential Pressure Regulator: Testing and Inspection

CIS-E III Control Unit Harness Connectors (Pin # Locations):

To check the function of the differential pressure regulator, it is necessary to measure the system pressure and monitor the control pressure and actuator current (differential pressure regulator current) simultaneously. To do this you will need Audi fuel pressure gauge part #VW 1318 or equivalent (or you can use two separate gauges. Gauges must be able to read up to 7.0 bar/103 psi).

Checking Differential Pressure:

1. Connect fuel pressure gauge as shown in diagram (special adapters may be necessary to do this).
a. Control pressure connection - Remove test plug and connect hose from pressure gauge (3) to lower chamber (control pressure) test port (1) on side of fuel distributor.
b. System pressure connection - Disconnect fuel line (2) from cold start valve and connect to valve block on gauge (or connect to separate gauge).

2. Disconnect electrical connector from differential pressure regulator.

3. With pressure gauge valve open, apply battery+ power to fuse #13 in fuse relay panel to energize fuel pump, and read and record system pressure (when using separate gauges, system pressure is read from gauge connected to cold start valve fuel line).
- System pressure should be 6.1-6.5 bar (89-95 psi). If not, fuel pump &/or primary pressure regulator are faulty.

4. Close valve on pressure gauge and leave differential pressure regulator disconnected.

5. Energize fuel pump and read pressure gauge (control pressure). When using separate gauges the control pressure is read from the gauge connected to the test port on the side of fuel distributor.
- Control pressure should be 0.3-0.5 bar (4.4-7.4 psi) lower than system pressure.

Remember, differential pressure is the difference between system pressure and control pressure.

6. Install Audi electrical harness adapter #VW 1315A/1 between differential pressure regulator and its harness connector.

Harness Adapter For Checking Differential Pressure Regulator Current:

Checking Differential Pressure Regulator Current:

7. Connect DVM to adapter, set mode to DC milliamps 200mA scale.

8. Turn ignition "on" and energize fuel pump (do not start engine).

9. Observe mA current and control pressure.
- Differential pressure regulator current (actuator current) should be fixed at 100 mA (whenever the ignition is on with engine not running) and control pressure should be 1.2-1.5 bar (17.6-22.1 psi) lower than system pressure.

If there is no mA reading or if reading is incorrect, check for:
a. Open circuit within differential pressure regulator. Check resistance through regulator, should be approx. 15-25 ohms. If not replace regulator.
b. Open or grounded circuit between regulator connector terminal #1 (R/Y wire) and fuel control unit terminal #4.
c. Open or grounded circuit between regulator connector terminal #2 (R/W wire) and fuel control unit terminal #5.
If wiring and regulator are OK, and there is still no current or incorrect current through differential pressure regulator, then the fuel control unit is faulty.

If the actuator current is correct but the differential pressure is not correct, then the differential pressure regulator is faulty, or the restrictor orifice in the lower chamber through-flow passage is plugged.

ACCELERATION ENRICHMENT CHECKING

Leave fuel pressure gauge(s) and DVM connected for this test.

1. Start engine and run at approx. 2,500 rpm constant speed.

2. Without changing throttle position, manually close full throttle switch and observe actuator current and control pressure.
- Actuator current should increase slightly and control pressure should drop slightly when full throttle switch is closed.