⚡ Understanding Spark Advance
Spark Advance (Ignition Timing) determines when the spark plug
fires relative to the piston's position. It is measured in degrees of
crankshaft rotation relative to Top Dead Center (TDC).
➕ Positive Values (Advanced Timing)
Definition: The spark occurs
BEFORE the piston reaches the very top (BTDC).
-
Context: This is the normal operating state for
producing power.
-
Why? The air-fuel mixture takes time to burn.
Igniting it early ensures the maximum explosion pressure hits the
piston exactly as it starts its downward journey.
-
Typical Behavior:
- Idle: +5° to +15°
- Cruising: +30° to +45° (High efficiency)
-
Full Throttle (WOT): +10° to +25° (Maximum
Power)
➖ Negative Values (Retarded Timing)
Definition: The spark occurs
AFTER the piston has passed the top point (ATDC).
-
Context: Generally inefficient for power, but used
for specific ECU strategies.
-
Common Scenarios:
-
Cold Start (Cat Heating): Modern engines delay
ignition (e.g., -15°) to burn fuel in the exhaust, heating the
catalytic converter rapidly.
-
Gear Shifts: The ECU momentarily pulls timing
(often to negative) during shifts to reduce torque and protect
the transmission (ZF 8HP).
🚀 Analyzing Full Throttle Data
When analyzing a log with 100% accelerator pedal position:
-
Goal: You want to see a smooth,
positive (+) curve (e.g., +10° to +25°).
-
⚠️ Knock Detection: If you see a "sawtooth" pattern
where timing climbs and suddenly drops by 3° or more (without a gear
shift), the ECU is likely detecting knock.
-
❌ Danger Zone: If timing stays at
0° or negative during a pull (and no gear shift is
happening), it indicates severe knock, extreme intake temps, or
engine issues.
📊 Quick Reference Table
| Value Range |
Meaning |
Status |
| +10° to +25° |
Full Throttle Acceleration |
✅ Healthy (Power)
|
| +30° to +45° |
Light Load / Cruising |
✅ Healthy (Economy)
|
| -10° to -20° |
Cold Start (First ~30s) |
✅ Normal (Warm-up)
|
| Sharp Drop (to -10°) |
Gear Shift |
✅ Normal (Smoothness)
|
| Sudden Drop (-3°) |
Knock Detected |
⚠️ Caution |
| Zero / Negative |
Full Throttle (No Shift) |
❌ Critical Issue
|
* Note: Values may vary slightly depending on engine tuning, fuel
quality (95/98/100 RON), and ambient conditions.