Cold Acceleration Enrichment - Volkswagen 1991 GTI L4-1984cc 2.0L DOHC (9A) Service Manual

To ensure smooth running, the injection system supplies additional fuel to the engine when cold, during the warm-up period, and full throttle operation by increasing differential pressure regulator current for a short period of time. The coolant temperature sensor provides the fuel injection control unit with the required engine temperature information needed for cold running enrichment. The throttle switch provides information concerning throttle position. The starter provides an additional signal to the control unit for after-start enrichment.

Diaphragm Pressure Regulator Testing Connections:

1. Connect an ammeter between the differential pressure regulator harness connector and the differential pressure regulator, using VOLKSWAGEN special tool #VW 1315A/1 or equivalent.

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:

2. Remove the harness connector from the coolant temperature sensor and bridge the connector with a 2500 ohm resistor to simulate a cold engine.
3. Disconnect the oxygen sensor harness connector.
4. Start the engine and let it idle.
5. Measure the differential pressure regulator current.

^ Differential Pressure Regulator current should be between 15 and 25 mA for approx. 6 - 9 seconds, then gradually drop to between 9 and 15 mA.

6. Open the throttle completely, then let it close.

^ Differential Pressure Regulator current should rise briefly.

If the correct measurement is not obtained check the CIS-E Motronic harness. Refer to SYSTEM ELECTRICAL TESTS. If the harness is OK the CIS-E Motronic control unit may be defective.

7. Erase the fault memory.