High Altitude Compensation System

High altitude compensation is a function of ECU. It provides timing advance according to altitude.

1. With engine warm, connect timing light to No. 1 cylinder. Check ignition timing. Timing at less than 3000 feet should be 7° BTDC.
2. Connect vacuum pump to atmospheric pressure sensor. Apply vacuum and check ignition timing. Timing should advance to 13° BTDC.
3. If not, inspect atmospheric pressure sensor and ECU. Ensure altitude is not greater than 3000 feet.