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. After-start enrichment lasts approximately 40 seconds. Cold running enrichment decreases gradually as the engine warms up, finally reaching the normal warm running value.

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.

Coolant Temperature Sensor:

5. Next, remove the harness connector from the coolant temperature sensor to simulate a cold engine. To check cold running enrichment, turn the ignition switch ON. Differential Pressure Regulator current should be:

80 to 110 mA

6. After-start enrichment is checked after operating the starter. To prevent the engine from starting during the test, disconnect the ignition coil wire from the center of the distributor cap and use a jumper wire to connect it to ground. Actuate the starter for approximately 3 seconds, then leave the ignition switch ON. The Differential Pressure Regulator current should increase to more than:

120 mA for 20 to 40 seconds then return to 80 to 110 mA

7. When the test is complete, turn the ignition switch OFF. Reconnect the coil wire and the coolant temperature sensor harness connector. Also disconnect the ammeter from the Differential Pressure Regulator.
8. These tests are only check the electrical portion of the Differential Pressure Regulator, to check the fuel pressure portion of the regulator Fuel System Pressure Test.