Differential Pressure Regulator: Testing and Inspection

1. First check the Differential Pressure Regulator internal wiring to be sure it's not faulty. Disconnect the harness connector from the Differential Pressure Regulator, check the resistance across the terminals of the Differential Pressure Regulator, correct resistance should be between:

17.5 and 21.5 ohms

2. If not the Differential Pressure Regulator is faulty and should be replaced before starting any further tests.
3. To ensure smooth running, the injection system supplies additional fuel to the engine when cold by increasing differential pressure regulator current for a short period after starting and during warm-up. The coolant temperature sensor provides the fuel injection control unit with the required engine temperature information needed for cold running enrichment. The starter provides an additional signal to the control unit for after-start enrichment. To ensure good throttle response when the engine is cold, the system also briefly delivers additional fuel when the throttle valve is opened suddenly.

Differential Pressure Regulator:

Diaphragm Pressure Regulator Testing Connections:

4. To test these functions, connect an ammeter between the differential pressure regulator harness connector and the differential pressure regulator, using VOLKSWAGEN special tool #VW 1315A/1 or equivalent. This will be used to measure differential pressure regulator current during this test.

CAUTION: The small female terminals in the differential pressure regulator harness connector are easily damaged. If fabricating a test harness, use the appropriate male terminals to make connections with the harness connector.

Oxygen Sensor Harness Connector:

5. Disconnect the oxygen sensor harness connector.

Coolant Temperature Sensor:

6. Next, disconnect the harness connector from the coolant temperature sensor and connect a 2500 ohm resistance across the connector terminals to simulate a cold engine. To check cold running enrichment, START the engine and let idle. Differential Pressure Regulator current should be between:

15 and 25 mA for 6 to 9 seconds

7. Then drop to between:

9 and 15 mA

8. To test cold acceleration enrichment, open the throttle completely, then let it close. Differential Pressure Regulator current should increase briefly, indicating cold acceleration enrichment.
9. When the test is complete, turn the engine OFF. Reconnect the oxygen sensor and the coolant temperature sensor harness connector. Also disconnect the ammeter from the Differential Pressure Regulator.
10. These tests are only check the electrical portion of the Differential Pressure Regulator, to check the fuel pressure portion of the regulator refer to FUEL SYSTEM PRESSURE TEST.