Long term fuel trim off

[Gmguy]

Do any of the base files for the mazda 6/atenza mps have the long term fuel trim disabled?

Have a vehicle that customer has removes the cat from

[mituc]

Removing the catalytic converter will not affect the fuel trims in any way, the primary O2 sensor is before the primary cat.
You can disable fuel trims entirely but I do not see how this would be a good idea.

[Gmguy]

That does not right to me, every other vehicle I have tuned uses rear 02 sensors for long term fuel trim calculations. Pre cat sensors are used for short term, this is why you can have a positive short term trim and a negative long term at the same time.

If these mps motors do not use that logic how to they calculate long term trims?

[mituc]

That does not right to me, every other vehicle I have tuned uses rear 02 sensors for long term fuel trim calculations.

Every manufacturer have their own approach on things. But to be honest I do not think that any of them use the secondary O2 (post-cat) for any sort of fuel trims readings (I'm only referring to "readings" - not biasing) because at that point the exhaust gasses are already chemically changed by the cats. However, the secondary O2 sensor readings may be used to alter the fuel trims logic for various emissions logic depending on the cats temp, or cats state or degradation, but never directly, at least as far as I know and learned from any EFI course I took so far.

For these mazda platforms the primary O2 sensor readings are used for both short and long term fuel trims, basically the fuel trims (or fueling deviations) are measured by that one sensor and based on the momentary deviations the ECU calculates the short term fuel trims, and then using a weighted average algorithm calculates the long term fuel trims for each MAF partition (so the LTFTs are not a direct result of the momentary lambda readings). The secondary O2 has a play in fuel trims calculation and even commanded AFRs in some situations (closed loop only).

[Gmguy]

The rear 02 sensor is used to monitor the cat efficiency though so obviously and engine running at say 12:1 is not going to be producing the correct input to the cat therefor the output will be wrong and the rear 02 sensor will allow the ecu to adjust for that. Pretty standard practice on all gm, ford, toyota and nissans that I have tuned that when removing the cat rear 02 controls and long term trims need to be disabled to prevent them from skewing mixture as the rear o2 will be reading exactly as the front 02 does

[Gmguy]

I guess as a work around I could unplug the rear 02 and disable the dtcs, that will ensure it has no influence at all on anything

[mituc]

I guess as a work around I could unplug the rear 02 and disable the dtcs, that will ensure it has no influence at all on anything

Yes, we actually do this on some cars, especially on those which we cant to use leaner mixture for cruising and low loads. With the secondary O2 still connected you can't go leaner than lambda 1.025 or something, at 1.03 the ECU starts freaking out because of the readings of the secondary O2. With the secondary O2 disconnected you don't have that problem.

The rear 02 sensor is used to monitor the cat efficiency though so obviously and engine running at say 12:1 is not going to be producing the correct input to the cat therefor the output will be wrong and the rear 02 sensor will allow the ecu to adjust for that.

If you're running 12:1 and commanding 12:1 then the secondary O2 will have no say in this (in closed loop, of course, because in open loop it will be totally ignored).