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04 WRX Fuel Maps

General Tuning Discussion

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Okay so here's the scoop,

I had a great tune on my car and then I relocated from NC - WA state. The car was tuned on 93 octane and now I can no longer get 93 as they only sell 92 octane here. I'm wanting to dial in my AFR for the different octane rating. I haven't made any adjustments yet because I was trying to get my AEM UEGO to connect and log via Accesstuner. I haven't done any WOT data logging since I got it connected and logging. My question is will I be applying my fuel correction factor to the Primary Open Loop Fueling map or is there more that goes into the big picture here? I have noticed the ECU has picked up on the octane difference and I'm getting fine knock learning in the early boost areas. I could do a WOT data log if it helps, just not too sure where to go from here. I will include the data log I got before I got the UEGO logging hopefully I have enough perimeters selected if I should add or take away for the next Log please let me know!

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Ok so first things first, the stoichiometric AFR doesn't vary measurably between different octane pump fuels so if the engine was tuned on 93 and you've changed to 92 you should still hit your AFR targets. The ignition timing however is a different deal. If you drop the octane rating of the fuel then you may find the engine knocks (which it seems you have found). This will require the timing maps to be adjusted anywhere knock is being logged. The Subaru timing is quite complex in that there is a base ignition table and then an advance map that the ECU can add on top of the base values. The amount of timing from the advance maps that the ECU adds will depend on the activity from the knock sensor and the resultant IAM or DAM (Ignition Advance Multiplier / Dynamic Advance Multiplier).

Different tuners have different preferences for how to deal with the ignition tuning but personally I do most of my tuning in the base ignition table and reduce and smooth the amount of timing advance available in the advance tables. The worked example in the Practical Reflash Tuning course covers this in detail on the FA20 engine which is identical from a timing basis.

Thanks that’s actually my next course to take so I’ll knock that one out and give it a shot