JSR_AP2

I've searched here and other boards and read through the threads explaining how a piggy-back fuel controller (A'pex V-AFC, Greddy E-Manage) works. I think I understand the jist of it, but still unsure. So, here's what I think I know and I'd appreciate it if the more knowledgable can either confirm my understanding or correct my mis-understanding:

Piggy-back fuel controllers only work in open-loop conditions such as WOT. Anything not WOT, the ECU operates under closed-loop via STFT and LTFT tables. So, is it correct to say that assuming you have engine mods and are running a piggy-back fuel computer, the OEM ECU adjusts appropriately via STFT and LTFT during part throttle (closed-loop)?

My confusion lies in what happens in closed-loop. Assume: your mods considerably increase flow, thus leaning out the AFR of the standard map. In open-loop (WOT), the piggy-back adjusts/accounts for that. In closed-loop, will the STFT and LTFT tables of the OEM ECU be able to adjust for all your mods (essentially doing in closed-loop what the piggy-back is doing in open-loop)?
Everyone always shows gains made with tuning, even on piggy-backs, on dynos, but those are always run at WOT. I'm not always at WOT, so I'm just wondering if I get similar gains at part-throttle because the OEM ECU is adjusting (tuning) accordingly.
Thanks (and sorry for my ignorance).

Wisconsin S2k

I believe many of these piggy backs DO have a closed loop fuel mapping control of some kind. In fact, if I remember correctly, the VAFC does both open And closed loop, having seperate adjustments you can make for both.

JSR_AP2

From every other resource I've read, the OEM ECU readjusts in closed-loop to negate the settings of the piggy-back.

deathsled

first of all, i believe WOT is closed loop. Part throttle operation is open loop. The ecu is able to correct somewhat, usually +-10-15% during open loop operation, but depending on the size of injectors, you will still need to bring them within range of the ECUs control with a piggyback.

the piggyback is working at all times, part throttle and WOT, closed loop and open loop operation. It works by modifying the airflow signal to the ECU to trick it into thinking their is more or less air entering the system, thus altering the fuel control

fperra

Sorry, but you got it backwards. WOT is open-loop, meening that O2 feedback is not being used. Fuel is controlled strictly by the fuel tables.

JSR_AP2

fperra: On HOnda ECUs, the STFT and LTFT readjust automatically during closed-loop to cancel out the piggy-back's adjustment. Does the OEM ECU adjust enough to compensate for the mods (e.g. tuning)?