As a car enthusiast and someone who enjoys digging into vehicle diagnostics, I recently experimented with an inexpensive wireless ELM327 OBD2 dongle and the Four Stroke app on my iOS device. My aim was to monitor ignition timing advance, especially to see if there were noticeable differences when using different fuel grades like premium V-Power, Momentum 99, and standard 95 RON. However, the readings displayed for “Ignition timing advance on cylinder #1” left me scratching my head, fluctuating from roughly -30 to +50 degrees.
The term “timing advance” itself suggests that positive values should represent advance, while negative values might indicate the opposite, perhaps timing retardation. Yet, the negative values felt counterintuitive in the context of ‘advance’. OBD Fusion, another app I tried, showed the same format, adding to the uncertainty.
My initial observations during driving were that the values tended to be negative at idle. Under light engine load, they climbed into positive territory, suggesting ‘advance’. Conversely, during hard acceleration, the readings dropped closer to zero, for instance, around +7 or +10, compared to +25 or +30 at lighter throttle. This behavior leaned me towards my first interpretation: positive numbers indeed signify timing advance, and negative numbers likely represent timing retardation from the base setting.
Despite searching through online resources like wikis, Google, and app documentation, I couldn’t find a definitive explanation. Therefore, I turned to the car community for clarity on interpreting these Obd2 Timing Advance readings.
To clarify, in the realm of engine mechanics, ignition timing advance refers to the number of degrees before Top Dead Center (TDC) that the spark plug fires. Advancing the timing means the spark occurs earlier in the compression stroke. This is typically done to allow the air-fuel mixture more time to burn, optimizing combustion and power, especially at higher engine speeds and lighter loads. Conversely, timing retardation means the spark occurs closer to or even after TDC, often used to control detonation (knocking) or reduce emissions under heavy load conditions.
When an OBD2 scanner reports negative timing advance, it’s generally indicating timing retardation. The negative value signifies degrees after a baseline or standard timing point, effectively delaying the spark. Conversely, positive values correctly represent timing advance, showing degrees before the baseline.
The readings you observed are consistent with typical engine management behavior. At idle, engines often use slightly retarded timing for stability. Under light load and cruising, the engine computer advances timing for better fuel efficiency and responsiveness. During heavy acceleration, the timing is often retarded again to prevent engine knock and protect the engine.
Therefore, your initial intuition was correct. In most OBD2 applications displaying “Ignition Timing Advance,” positive numbers indicate degrees of advance, and negative numbers represent degrees of retardation. It’s always best to consult your vehicle’s service manual for specific expected ranges and interpretations for your engine, but this general understanding should help you accurately monitor and interpret your OBD2 timing advance readings.
