Torque

Forums

Forums

Guest  

Show or hide header
Welcome Guest, posting in this forum require registration.




Torque » Torque OBD ECU Scanner » Torque Discussion / Ideas » Fuel trims

Pages: [1]
Author Topic: Fuel trims
K7878
Member
Posts: 3
Post Fuel trims
on: May 16, 2020 (GMT)

Hi guys,

I’m trying to start analysis of parameters of my engine, and I know that I need to focus on short and long fuel trims, but in TorquePro I have a few options: STFT, LTFT for each bank, but what is e.g. “Fuel trim bank 1 sensor 1: F/T 1×1” also expressed in %? I supposed that it is the same thing as STFT on bank 1, but after some data logging I see that values are different on these two, and also I cannot see any clear relation between STFT1, LTFT1 and “F/T 1×1” values. What’s actually “F/T 1×1” means and how it can be useful apart from STFT and LTFT during car diagnosis?

Thanks in advance,

moreause
Member
Posts: 480
Post Re: Fuel trims
on: May 17, 2020 (GMT)

short story

short trim is moving rapidly and it mostly for the day to day temperature ans condition variation

if for some reason it is always to high or to low…

then the long trim value will be change to recenter the short trim around zero (remember short story)

for bank 1 or bank 2 depend on your engine/exhaust design

inline 4 only have 1 exhaust so 1 bank

v6 and v8 have 2 exhaust so 2 bank

for the other value …don’t know

Capp777
Member
Posts: 2813
Post Re: Fuel trims
on: May 17, 2020 (GMT)

Its my understanding that F/T 1×1 represents the
fuel trim associated with that specific O2 sensor
whereas the STFT1/LTFT1 represents the correction
for bank 1, etc.

Recently diagnosed a 2000 Ford Focus with max’d
out fuel trims at idle which returned to almost
normal at speed. Found vacuum leak to be
source of problem. Crack in hose.

K7878
Member
Posts: 3
Post Re: Fuel trims
on: May 18, 2020 (GMT)

Thank you both for your replies,

it’s still quite confusing for me, but when reading your answers another question came to my mind: do you think that STFT (for bank 1 for example) is being calculated with more input signals/parameters than o2 sensor and that “F/T 1×1” is only one of them? I used to think that STFT1 is based only on signal from pre-cat oxygen sensor 1×1 (bank1), which is called just “F/T 1×1” in my understanding.
I will observe only STFT dials then, but I’m still quite curious about the difference. Especially that “F/T 1×1” seems not correspond to the voltage measured on “O2 sensor 1×1”

Capp777
Member
Posts: 2813
Post Re: Fuel trims
on: May 18, 2020 (GMT)

If you use TorqueScan to view the 01xx
pid assigned to each, maybe Wiki OBDII Pids
would help understanding.

Tux
Member
Posts: 8
Post Re: Fuel trims
on: May 18, 2020 (GMT)

The OBD2 standard defines two (Mode 01) PIDs for STFT on bank 1: 06 and 14 (hexadecimal). PID 06 is “STFT for Bank 1” and (per SAE J1979) is “the correction being utilised by the closed-loop fuel algorithm”. That’s the one I’d be looking at. PID 14 is the STFT associated with Bank 1 O2 Sensor 1.

I strongly suspect that ‘Capp777’ is correct, which probably means that the Torque Pro’s “STFT1” PID is OBD2 Mode 01 PID 06 and TP’s “F/T 1×1” PID is OBD2 Mode 01 PID 14. But the only way to know for sure is for Torque’s author (Ian Hawkins aka ‘piemmm’) to clarify or to connect Torque Pro to an OBD simulator.

What vehicle are you testing on? And under what conditions (engine speed, engine load, vehicle speed, etc)? You said that there’s a difference in the 2 STFT values you logged. But just how much do they differ? I have graphs taken (not using Torque) on an idling 2005 GM Buick, after the vehicle has warmed up enough to be running in closed-loop mode. They clearly show that those two ‘Bank 1’ STFT PIDs (06 and 14) track each other almost perfectly, with only a couple of very minor differences (of very short duration and very small amplitude change). I would expect other vehicles to be similar, but I’m fully prepared to be surprised and I expect to eventually test other vehicles. Also, I’d like to test again at various RPMs and engine load conditions.

Lastly, don’t expect to find any obvious correlation between the O2 sensor voltage (which merely reflects the oxygen content in the exhaust) and the STFT (regardless of which STFT PID you’re querying). Yes, the PCM certainly uses O2 sensor voltage in the STFT calculation, but there is undoubtedly more to it (e.g. engine RPM, etc). My semi-extensive testing shows no obvious, direct correlation.

If it were me, for STFT, I’d use whatever you suspect to be the PID 06 value and (mostly) ignore the O2-sensor-specific fuel trim value(s).

Whatever you decide, good luck on your diagnosis!

K7878
Member
Posts: 3
Post Re: Fuel trims
on: May 18, 2020 (GMT)

Thanks for great answers,

I’m testing BMW E60 but let me dig into it a bit more in various conditions to check again the real difference between these two STFT values. So all of you were right

F-150Torqued
Member
Posts: 423
Post Re: Fuel trims
on: May 20, 2020 (GMT)

No added confusion intended. But my 2004 F150 5.4L Triton has a Pid for EACH bank called “Rear Fuel Trim 1” and “Rear Fuel Trim 2”, at PID No. hex 163E and 163F respectfully. Both two bytes in length, formula Signed(A)*256+B, produces a percent result between 0 and 100 percent – and react quiet large and dynamically. I just include them on my Fuel Trims dashboard for more information (or confusion).

There is NO 3rd sensor on each bank on my truck, but OBDII, and some vehicles, support it. I have not analyzed it extensively nor have any idea how the PCM calculates it – but I suspect it (along with LTFT1 would play a part in any variation between STFT1 and F/T1x1.

——————————

54371019

Pages: [1]
WP-Forum by: Fredrik Fahlstad, Version: 2.4
Page loaded in: 0.186 seconds.

  Follow me on twitter