High Negative LTFT on N/A BRZ causing idling issues

[paintdude258]

I appreciate the response @steve99 I am working on getting in a good data log to use the MAF scaling tool talked about in your article.

Is there any reason why my scaling would be off now, even after I've ran the same tune for about 6-7 months now?

Edit: I am going to purchase a custom tune from you guys at Openflash probably Monday or Tuesday!

[steve99]

Originally Posted by paintdude258

I appreciate the response @steve99 I am working on getting in a good data log to use the MAF scaling tool talked about in your article.

Is there any reason why my scaling would be off now, even after I've ran the same tune for about 6-7 months now?

Edit: I am going to purchase a custom tune from you guys at Openflash probably Monday or Tuesday!

did you ever log it after you put new intake on ?, ltft can takje about 100 miles or so so settle depending on what type of driving your doing.

also large changes in ambient temps can move ltft 5% or more like winter to summer

[paintdude258]

I have never logged any data because I have never had any problems with my car up until recently.

The intake was the first thing I put on the car. I ran the intake 2 months before I did the headers and the tune.

The fuel trims only started going crazy about the last month or so.

To make sure it wasn't the intake, I ran the car today about 15 minutes with the intake unplugged. I took off the battery and purged the charge, then proceeded to run the car another 30 minutes or so with just the air straightener and the MAF plugged in! Trims settled right at the same -15% - -20%

[steve99]

Originally Posted by paintdude258

I have never logged any data because I have never had any problems with my car up until recently.

The intake was the first thing I put on the car. I ran the intake 2 months before I did the headers and the tune.

The fuel trims only started going crazy about the last month or so.

To make sure it wasn't the intake, I ran the car today about 15 minutes with the intake unplugged. I took off the battery and purged the charge, then proceeded to run the car another 30 minutes or so with just the air straightener and the MAF plugged in! Trims settled right at the same -15% - -20%

Hmmm
could be bad maf or 02 sensor, you might want to log afr and see what that looks like vs commanded afr. but yeah could be bad sensor or connection.

exhaust leaks usually send trims poisitive as o2 sensor sees fresh air then thinks is lean so ecu compensates with poisitive trims to add fuel

[paintdude258]

So to check if my o2 or MAF sensors are bad, what should I log?

Do a 1-3 gear pull with AFR, Command AFR, and anything else?

[paintdude258]

@steve99 how do I check for a bad o2 sensor? I read somewhere that wideband AFR could shed some light, but that parameter only reads 17 at all times.

[steve99]

Originally Posted by paintdude258

@steve99 how do I check for a bad o2 sensor? I read somewhere that wideband AFR could shed some light, but that parameter only reads 17 at all times.

If you have oft you can monitor rear 02 sensor by logging "wideband AFR" while its not calibrated for stock o2 sensor you should see the reading move arround from idle to wot. It may not follow the front o2 sensor well ie AFR reading but the rear should change. If it does not you have a stuffed sensor , wiring problem or a bad exhaust leak.

you might also be able to log rear 02 sensor volts which should change.

assuming the oft logging is set up correctly for your rom.

[paintdude258]

@steve99 My seconday o2 sensor volts read 0, and my Wideband AFR reads 17 all of the time.

This would appear to by my culprate.

Moving forward, i can either replace that o2 sensor, or i can purchase the Bosch wideband that the OFT is programmed to read. My question is that if i splice into the current rear 02 signal wire with the Bosch wideband, will the data sent back to my ecu do the same thing as the stock sensor, or will it be a completely different read out all together.

I dont want to buy the wideband and it not fix my problem. If this is the case, i will just get an OEM replacement.

On another note, i do plan on getting a custom tune from you guys soon, so with the small price difference, i figured the wideband would give you, the tuner, a more accurate reading to tune with.

Thank you for all your answers steve, really helped me along the way.

[steve99]

Originally Posted by paintdude258

@steve99 My seconday o2 sensor volts read 0, and my Wideband AFR reads 17 all of the time.

This would appear to by my culprate.

Moving forward, i can either replace that o2 sensor, or i can purchase the Bosch wideband that the OFT is programmed to read. My question is that if i splice into the current rear 02 signal wire with the Bosch wideband, will the data sent back to my ecu do the same thing as the stock sensor, or will it be a completely different read out all together.

I dont want to buy the wideband and it not fix my problem. If this is the case, i will just get an OEM replacement.

On another note, i do plan on getting a custom tune from you guys soon, so with the small price difference, i figured the wideband would give you, the tuner, a more accurate reading to tune with.

Thank you for all your answers steve, really helped me along the way.

Haha, i dont work for oft :-)

if you replace rear 02 with wideband you might have to do a bit of work with tune as the ecu is expecting a narrowband signal from that sensor.

its far easier to just rescale the stock Front o2 sensor to read more wideband.


its possible the oft logging is not set up for your rom and that may be why it reads 0v and rear afr does not change, but coupled with your other issues it does point to the rear 02. If you know someone with the same car you could test oft on that and maybe even take some resistive measurements off their rear 02 to compare with yours.

maybe even swap the black and grey plugs for front rear o2, the car will run like crap and thow a cel but if you start it it should show a reading for rear 02 on oft and the front o2 should read 0v, just to confirm before you shell out for a new rear sensor

[jwvand02]

Originally Posted by paintdude258

@steve99 My seconday o2 sensor volts read 0, and my Wideband AFR reads 17 all of the time.

This would appear to by my culprate.

Moving forward, i can either replace that o2 sensor, or i can purchase the Bosch wideband that the OFT is programmed to read. My question is that if i splice into the current rear 02 signal wire with the Bosch wideband, will the data sent back to my ecu do the same thing as the stock sensor, or will it be a completely different read out all together.

I dont want to buy the wideband and it not fix my problem. If this is the case, i will just get an OEM replacement.

On another note, i do plan on getting a custom tune from you guys soon, so with the small price difference, i figured the wideband would give you, the tuner, a more accurate reading to tune with.

Thank you for all your answers steve, really helped me along the way.

My understanding is that the rear O2 sensor should not impact fueling at all, and that the car should only be adjusting fueling based on the primary.

High negative fuel trims mean that your O2 sensor is not seeing as much oxygen as expected, which makes me think an intake/exhaust leak or more free-flowing intake is really unlikely to be the culprit. I dealt with all of the above and routinely saw high fuel trims, not low.

My gut says there's something weird going on with your primary O2 sensor or MAF. I'd log the voltages on both, as well as AFRs and both short and long term trims and compare to a log for a similar car. If I had to bet, I'd say the the MAF is fouled. If that oil you used to clean the filter got on it, it can definitely cause it to read off.

[paintdude258]

@jwvand02 awesome response. Could I just replace my MAF with another friends MAF who has a BRZ, and see if the fuel trim readings stabalize?

[jwvand02]

Originally Posted by paintdude258

@jwvand02 awesome response. Could I just replace my MAF with another friends MAF who has a BRZ, and see if the fuel trim readings stabalize?

Absolutely - if you have access to a friends BRZ I'd try that and the primary O2 sensor and see what happens.

Also, I'm not 100% sure about this but this is my experience and my best rationalization of it - when I fixed an issue allowing extra oxygen in, the short term trims were off for a short while in the opposite direction. In other words, if you replace one of the sensors and see high positive short term trims, don't panic you likely found your problem.

[steve99]

Originally Posted by jwvand02

My understanding is that the rear O2 sensor should not impact fueling at all, and that the car should only be adjusting fueling based on the primary.

High negative fuel trims mean that your O2 sensor is not seeing as much oxygen as expected, which makes me think an intake/exhaust leak or more free-flowing intake is really unlikely to be the culprit. I dealt with all of the above and routinely saw high fuel trims, not low.

My gut says there's something weird going on with your primary O2 sensor or MAF. I'd log the voltages on both, as well as AFRs and both short and long term trims and compare to a log for a similar car. If I had to bet, I'd say the the MAF is fouled. If that oil you used to clean the filter got on it, it can definitely cause it to read off.

While the front 02 sensor is the primary fueling sensor, the rear sensor also effects cruise fueling and weird stuff will happen if you disconnect or the rear 02 sensor is faulty, unless you disable the AF#3 corrections in the tune and disable some cel codes.

@paintdude258 log your Commanded AFR vs AFR as well as fuel trims. If the AFR looks ok ie around 14 cruise 13 mild acceleration and 11-12 wot and following commanded AFR reasonably well then the front o2 is likely ok, but for some reason the ecu is applying big correction to make that happen. That could be intake or exhaust leak, dirty MAF sensor etc.

[Wepeel]

Originally Posted by steve99

Haha, i dont work for oft :-)

if you replace rear 02 with wideband you might have to do a bit of work with tune as the ecu is expecting a narrowband signal from that sensor.

its far easier to just rescale the stock Front o2 sensor to read more wideband.


its possible the oft logging is not set up for your rom and that may be why it reads 0v and rear afr does not change, but coupled with your other issues it does point to the rear 02. If you know someone with the same car you could test oft on that and maybe even take some resistive measurements off their rear 02 to compare with yours.

maybe even swap the black and grey plugs for front rear o2, the car will run like crap and thow a cel but if you start it it should show a reading for rear 02 on oft and the front o2 should read 0v, just to confirm before you shell out for a new rear sensor

Shiv told me that on the OFT the O2S2 and Wideband AFR readings are not accurate - fwiw. O2S2 will always read 0.0v.