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 degrees BTDC.
2. Connect vacuum pump to atmospheric pressure sensor. Apply vacuum and check ignition timing. Timing should advance to 13 degrees BTDC.
3. If not, inspect atmospheric pressure sensor and ECU. Ensure altitude is not greater than 3000 feet.