RomRaider

I have recently rescaled my front O2 with an additional data point (04 WRX).

I bumped off the furthest right column, it is something like 25:1 AFR and I don't see how that could happen anyways.

My scaling table and a data log comparing it to LC-1 is attached. I have not touched any other data points besides the one.

Did anything ever come of this?

If you are looking for a wider AFR readings just log stock AFR sensor current.

There are a couple of limiters - sensor current (or derivative voltage) table edges in AFR sensor calibration table (those are evident) and min and max limits, that could not be located without code disassembling. The last means that those limits may not present in your particular ecu definition.

If definitions for all those tables exist you may expand stock AFR reading.
But you could not know for sure how ecu will interpret those expanded values.

I realize I'm horribly late to this discussion, but this is exactly what I've been trying to troubleshoot for the last month, or so. Having relocated the front O2 sensor to the downpipe, I've ended up with an oscillation in the hot idle, leading to stalling occasionally. After moving the O2 sensor back to the manifold, the oscillations seem to have calmed down a bit, and I haven't gotten a stall (yet - I haven't driven it much since).

Car is an '06 STI, and I'm a little confused as to how the front O2 scaling table has anything to do with the latency of the resulting idle fuel adjustments (unless the table is 'off' from the factory).

Trying to bring an old thread back to life.
I have an EDM 07 STi (EJ257) with an LM450 twinscroll setup. With that my OEM oxygen sensor is moved to the downpipe (nothing unique yet) and I see very erratic oscillation in AFR between ~14 and ~16 (not sure if this is unique). I am actually trying to solve this for quite some time, and my last trial was (based on a friend's suggestion) to replace my original oxygen sensor with a Spec-C oxygen sensor.
The scaling of the two sensors are very different, but after making the Spec-C sensor wiring to fit my bulkhead wiring loom, I changed the scaling and was very disappointed with the result. Not with fact that the oscillation did not improve, but it seems to me that the -1.38mA sensor rich limit (or some direct derivative parameter of that) is hardwired into the ECU (or in the code).
The reason why I think so is because even after rescaling the front oxygen sensor and moving the rich limit down to 5 (just for the sake of testing), the AFR readings were pegged at 14.16 and the AF sensor 1 current was pegged at -1.38mA.

Does anyone have any idea if this is some hardware limitation of the EDM (and I guess USDM) STi ECU (mine is AD8K100Z) or might there be some more tables involved in this logic? If the later is the case, I would appreciate if somebody could help to dig this out for me.

Thanks,
Béla

You may not use first generation Denso AFR sensor instead of the second one.
They have completely different heater current and calibrations.
And need \ use different electronics to run the sensor.
Thus sensor rescaling is not a solution.

Your setup needs close loop control ( proportional and integral factor ) to be modified since the sensor delay rises with sensor moved to downpipe.

Thank you Sasha.
So what you are saying is that this limit is hardware based, due to circuit design. Right?

Now, when you say proportional and integral factors of the closed loop. Are you talking about the turbo dynamics tables?

Sent from my SM-G930F using Tapatalk

I am talking about fuel correction closed loop control.

These are the compensations available in my rom. Do you mean these? If not it would be great if you could point me to some threads discussing that, so I can add those to my defs and see what I can do with them.

Thanks again.

Sent from my SM-G930F using Tapatalk

This looks like the correct thread (and audience) for my query...

My Front O2 sensor has died; I have 4 spare Bosch LSUs, but they are all 5 wire (or 6 wire if you include the "calibration resistor").

I understand the need for sensor relocation (due to pressure / etc.), so the sensor is already re-located post-turbo, I also understand that the calibration tables (mA) in the ECU would need altering (I have already done my research here and elsewhere), but what I can't determine for sure is if there is electrical / hardware compatibility. The LSU has:

* 2 wires for heater
* nernst sensor wire
* ion pump wire
* common ground
* calibration resistor

The heater wires can be pin matched, I guess the calibration resistor can be discounted if the ECU has a free air calibration strategy (anyone confirm this?) and the common ground can be the exhaust system / sensor body. Question is over the sensor and pump wires, I don't know the current mechanics of the four pin connection for the stock O2 (aside from the heater). From looking at the FSM it appears the stock 4 wire loom has provision for heater + / - and two other wires, I'm assuming the stock Denso also has this internal pump mechanism and so the remaining two stock wires would match to the nernst / pump wires to the Bosch sensor?

I think you all know what I'm getting at - so can anyone confirm if any of the above is possible or if it's just a case of sucking it up and getting a Denso sensor?

ref:
http://www.partinfo.co.uk/files/4%20Wir ... ensors.pdf
https://www.aa1car.com/library/wraf.htm
https://wbo2.com/lsu/im/lsu4pins.gif
https://wbo2.com/lsu/lsuworks.htm

I've been wondering the same thing.

I do not think that the OE ECU can use a universal exhaust gas oxygen sensor in place of the A/F sensor without some extra circuitry.

I have not read the rest of this thread, so this may have already been covered.

A pedantic explanation:

As I understand, the four wire OEM sensor is just a standard heated exhaust gas oxygen sensor. This is a thimble-shaped (or planar film, if its a newer sensor) zirconia cell with large surface-area platinum electrodes on either side (these are two of the wires). Inside the thimble is a heater trace (providing the other two wires). Such a sensor can be operated in constant current mode (as the downstream catalyst monitor sensor is) or in constant voltage mode (as the upstream A/F sensor is).

When in constant current mode, the current level is often chosen at zero and the signal which is monitored is the voltage output. Since electrochemistry is governed by the nernst equation, this operating mode produces a non-linear output that switches fast near stoichiometric A/F. This is not quite ideal, but is simple (i.e. cheap) and workable. If sensitivity to the stoich level is what is interesting, then this operating mode is good enough.

When in constant voltage mode, the same nernst cell is actively pumping oxygen and the signal of interest is the measured current (which is proportional to the amount of oxygen being pumped). Care must be taken when choosing the voltage level such that only oxygen is pumped- increased pumping voltages can split other oxides (of carbon, sulfur, hydrogen and nitrogen, for example) or even reduce the zirconia (this permanently damages the sensor). When oxygen delivery to the zirconia is diffusion-limited, this operating mode produces a linear output until the gas mixture is too rich- when such small amounts of excess oxygen are present, the sensor output is dictated by the other oxides that are being split to provide oxygen for pumping. Although the output is linear, the gain is different depending on whether the exhaust gas is lean or rich. Additionally, both lean and rich operation results in increased pumping current so it is hard to distinguish between lean and rich. If the voltage is such that no other oxides are split when in rich conditions, then we don't know how rich the gas mixture is.

This was the motivation for creating the five wire UEGO sensor. This device uses a feedback circuit (probably just an op amp) to controllably pump oxygen into a small chamber within a ceramic sensor element. The device has a nernst cell in constant current operation - the output voltage of this cell drives the op-amp, which takes this feedback to adjust the voltage driving the oxygen pump. The oxygen pumping current will be directed into or out of the small chamber (using another electrode) depending on the driving voltage. The pumping current is then proportional to the amount of oxygen which must be added to or removed from the chamber near the nernst cell. The output is linear, and the direction of the current flow tells you if the exhaust gas is lean or rich. This differs strongly from the 4-wire sensor in that it is neither constant current nor constant voltage.

When I said that extra circuitry was needed, here is what I mean: The OE ECU does not contain the circuit needed to run the UEGO as intended, so you would need to add that circuit and convert its output to be compatible with the OE ECU.

In principle you could use the nernst cell in the UEGO in the same operating mode as the OE sensor, but the signal magnitude would be smaller due to the much smaller surface area of the electrode, and there would be gas-response delay since the nernst cell is buried in an internal chamber behind a diffusion barrier. Further, if the UEGO does not have an air reference like the 4-wire sensor, then I'm not sure where you would be pumping the oxygen to (some internal part of the UEGO ceramic element).

Since that should not work well, it would be best to add circuitry to run the UEGO as intended, then convert the output to a current that can be read by the OE ECU. Some aftermarked UEGO controllers (like the Innovate one) provide an analog output that can be read by many OE ECUs - this would be a direct substitution for a constant current operation HEGO. Unfortunately, the Subaru ECU runs the A/F sensor in constant voltage mode and measures current. It is possible to create a goofy resistor ladder or op amp circuit to convert the voltage output of the aftermarket UEGO controller into a current.

However, if you wanted to put forth the effort, you could create your own UEGO controlling circuit based on an op amp. Then, you would design the device to output its pumping current directly to the Subaru ECU. The only tricky part here is that some ECUs use impedance measurements on the nernst cell of a 4-wire sensor in order to measure sensor temperature (and they control the heater based on this). If this was the case, the 'constant' voltage operation of the OE A/F sensor would not be properly integrated with the new circuit.

You have saved me from a pointless experiment, I have twin scroll setup in me EDM MY07 FXT and noticed same issues with the stock sensor





I ques the question is, where can one find a guide to dial in stock 32bit O2 for twin scroll application, with the sensor relocated to the DP?

Looking for solution for 32bit ECU and stock o2 sensor fitted in Downpipe