Quote:
Originally Posted by RadioFlyer
Interesting - I'm basing my post on first hand experience with an 08 G37, is the ECU different on the Z? If it's det/preignition, increasing octane isn't the fix, it just let's you know that it's a combustion problem. What happens if the octane booster stops the pinging? It will only stop it until the tank is empty again. And unless the OP wants to run octane booster at every tank, it'll come back on the next tank. ...Unless the ECU has a way of adjusting for it. And the ECU isn't going to adjust for it unless it sees the problem, which it won't if you're running octane booster.
Between STFT, and LTFT, the ECU has a VERY wide range of compensation. So first it adjusts the STFT, and then if it keeps riding the same compensation when the same conditions are present, then it starts turning that into LTFT. And as far as ECU compensation, my understanding is that it pulls timing based on the knock sensor (so knock pulls timing, while closed loop adjusts fuel based on it targeting stoich). The conditions described by the OP - light throttle, idle, light load, all point to closed loop operation. So the ECU would be adjusting fuel if it's lean. At least that's what I've seen.
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It has compensation for fuel trim based on AF sensor feedback (not knock) but it is a much slower learning process and once learned it will store and save that memory untill reset. This is why it would not be a fuel "trim" issue as it would have been learned already and would have to be running pretty damn lean to cause pre ignition (more than likely DTC set). This is why it is more than likely normal and just the ign map pushing the system to the edge of efficiency and having to pull back a little when/if it knocks as timing is not a "learned value" and constantly changes and tries to stay in the base map.
All the higher octane recommendation is to either proof true or faulse if it is pre ignition. It is a test not a long term fix, unless you wish to run higher octane all the time. Cheaper route is to either go with a custom tune for 91 or just accepte that it is pushing timing to the edge at light throttle tip in.