Engine Controls - Slight Hesitation on Acceleration

NUMBER: 11-58-99

DATE: 01/31/00

APPLICABILITY:
Some 99 MY Legacy and Impreza Manual Transmission Vehicles with 2.2L & 2.5L Engines.

SUBJECT:
Hesitation on Acceleration

In the event you encounter a customer complaint of a slight engine hesitation, perform the following:

First, eliminate all external influences, such as an incorrect or dirty air filter, loose or cracked intake duct, dirty fuel filter, low fuel pressure, PVC system, or low engine vacuum that would indicate an external leak or an internal engine component. Check for trouble codes and repair as necessary. Verify the fuel quality.

If all external components are confirmed to be operating within vehicle specifications, the hesitation may be caused by the ignition control logic in the ECM. Under certain low rpm driving patterns, the ignition control system can pickup engine vibrations through the knock sensor and may retard the ignition timing. This ignition timing is learned by the ECM and placed in memory. Note: This area of the memory can not be "viewed by using the Select Monitor. When the vehicle is driven under these conditions, the timing may be retarded and could cause the engine to hesitate on acceleration.

To confirm this condition, road test the vehicle while viewing the knock sensor signal on the Select Monitor. If you duplicate the hesitation and the reading on the monitor is around -10 Degrees, you will need to change the ECM to correct the concern.





Use the chart shown to locate and order the correct part number for your application.

Note:
Refer to the Warranty Labor Time Guide for claim information.





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