millinnium
New member
SHOnUup said:
Hi all, I asked the question in the FORScan Forum (you can look that up in the FORScan forum as its not that big just yet) and even the guy behind FORScan does not know the algorithm. But he did point out for me that the range for the reading is -200% to 200%. So far only the FordST Forum (http://focusst.net/threads/want-to-data-log-or-monitor-your-focus-st-this-is-how.161/) had some mention of the range whereby -1.0 (-100%) = High Octane, and 1.0 (100%) = Low Octane RELATIVE to your car's tuned octane rating. I suspect you should not expect to see 100% consistently, because what i understand is that the car ECU will re-learn the relative octane after acceleration when you decelerate. The other thing to note here is, you should be expecting a close to 0% range when filling your car up with the car's recommended fuel octane. i.e. the car's default tuned Octane.
I also looked into stuff like FoCCCus (a Ford Focus ECU Editor and Reader) to find that even though the car manual and dealer says that the car is designed for 91 Octane Fuel and 10% ethanol blend fuel, the actual ECU setting was 95 Octane! So, I will also caution that finding what the actual fuel octane setting in the car is not a simple matter of asking the dealer or reading the car manual.
For me, this PID is most useful to gauge your fuel octane RELATIVE to what the car is tuned for. For example, my car is tuned for 95 Octane, if I fuel up with good quality 91 Octane Fuel, I see the learned octane % hover around -5% to 50%, with I fill up with so called '94 Octane fuel' (blend fuel with up to 10% ethanol), the learned octane % actually jumps far to the 80% range (indicating lower octane) which makes sense, since the actual fuel IS lower octane, but because it is blended with up to 10% ethanol, it is then claimed 94 Octane. I also note that the LTFT (Long Term Fuel Trim) will show a reduction in % by up to 2-3% when filling up with 91 Octane fuel versus the so called 94 octane blend of fuel and ethanol.
I hope this helps.
And to make it clear once and for all, the Learned Relative Octane Adjust does not tell you what the octane rating of the fuel. AKA 93% Reading on the PID is NOT 93 Octane. In fact, no one can confirm what the exact algorithm is just yet, other than Cobb Tuning that seem to have figured something out. Wonder if anyone has ties with them that can ask what algorithm they use.
