02 sensor performance loss?

**razer900** · 08-27-2010, 08:50 AM

Did a header swap this spring and deleted the rear 02's with a tune. Instead of buying the bosch 13111 sensors i just used the old ones with extensions. I keep getting the 133, 134, 153, 154 coming up on the scanner now. I will be throwing new sensors in when i can find a set soon. My question is how much loss of performance iam i losing right now with the old worn out sensors? The car runs great, idles great, starts on the first spin, and has loads of power. Is there any power iam missing out on right now? Any comments greatly appreciated, thanks

**pajeff02** · 08-27-2010, 08:58 AM

On startup, your car is running in open loop and is not accepting feedback from the O2 senders. It is after a certain engine temp is attained that it switches over to closed loop. The only way to tell what the senders are doing is to connect a scanner and watch their output. They should rapidly cycle up and down. A bad sender may act lazy and have a slow rate of change. You can also use a wideband to check your A/F ratio as that is also indicative of what may be going on. Unfortunately, lots of other factors affect A/F and it is more difficult to diagnose the actual issue without a scanner.

**razer900** · 08-27-2010, 10:06 AM

So your saying that the sensors are lazy and slow responding, i will def throw on a new set and see what happens, but do the old slow lazy sensors have an affect on performance?

**35th-ANV-SS** · 08-27-2010, 10:27 AM

Your O2 sensors monitor the exhaust gases. They in turn send a voltage signal back to the PCM to let the PCM know whether the car is running lean or rich. Your PCM adjusts fuel accordingly based on this read out.

Therefore, if you have faulty O2's, your car probably is not running to its highest potential.

Running a little rich is not the end of the world. However, running lean is something that needs to be addressed immediately. By your statements above, it doesn't sound like you are running lean though.

**razer900** · 08-27-2010, 10:55 AM

good explanation! making more sense now, thanks! Iam hoping a new set of sensors and deleting the o2 extensions should clear up the problem. Altho the car runs great and everything i just dont know what kind of hp/performance iam leaving on the table running the old sensors

**LSXZ28** · 08-27-2010, 03:13 PM

O2 sensors only feedback during part-throttle... during WOT, the PCM goes into open loop and the O2 sensors do nothing. So, they may be effecting your part-throttle performance and fuel mileage, but not the WOT performance...

**pajeff02** · 08-27-2010, 06:35 PM

Originally Posted by LSXZ28

O2 sensors only feedback during part-throttle... during WOT, the PCM goes into open loop and the O2 sensors do nothing. So, they may be effecting your part-throttle performance and fuel mileage, but not the WOT performance...

Good point.

**0rion** · 08-27-2010, 06:54 PM

Originally Posted by LSXZ28

O2 sensors only feedback during part-throttle... during WOT, the PCM goes into open loop and the O2 sensors do nothing. So, they may be effecting your part-throttle performance and fuel mileage, but not the WOT performance...

incorrect....kinda. You're correct that the car goes to open loop during WOT but the O2's do have an impact via fuel trims on final fueling. If you're showing lean in the cell prior to going open loop then the pcm adds that % to the final fueling.

**pajeff02** · 08-28-2010, 03:42 AM

Originally Posted by 0rion

incorrect....kinda. You're correct that the car goes to open loop during WOT but the O2's do have an impact via fuel trims on final fueling. If you're showing lean in the cell prior to going open loop then the pcm adds that % to the final fueling.

Question: Why do tuners delete the LTFT's?

**LSXZ28** · 08-28-2010, 04:34 AM

Originally Posted by 0rion

incorrect....kinda. You're correct that the car goes to open loop during WOT but the O2's do have an impact via fuel trims on final fueling. If you're showing lean in the cell prior to going open loop then the pcm adds that % to the final fueling.

That is true - posative LTFTs from a lean or percieved lean condition are carried over to WOT. Good catch! That is another reason it is important not to have exhaust leaks!

**LSXZ28** · 08-28-2010, 04:57 AM

Originally Posted by pajeff02

Question: Why do tuners delete the LTFT's?

The only time I would permanently disable LTFTs would be on a race car or a car where the exhaust leaks are bad and skewing the feedback causing un-needed extra fuel to be added (and then they would be turned back on after the leaks are fixed)... During tuning, they are diabled so you are getting wideband readings straight from the tune with no narrow band feedback...

**0rion** · 08-28-2010, 08:26 AM

Originally Posted by pajeff02

Question: Why do tuners delete the LTFT's?

Are you talking about disabling them in the tune or clearing them prior to logging? I have mine disabled on my car because I've done enough logging that my fueling is pretty dead nuts and I have a wideband so I watch my AFR all the time. Once you get the fueling dead on you really don't need the ltft's but I'm not comfortable doing that to others cars so I don't disable them normally.
You clear them prior to tuning so they don't have any input on your fueling.

**pajeff02** · 08-28-2010, 08:48 AM

Maybe that's what it was about -- clearing them so you get an unaltered A/F straight from the tune. Thanks!

**Frost** · 08-29-2010, 04:28 PM

I very regularly disable them.

They are a factory crutch for aging parts, differences between vehicles, environmental variables and much more. Even with LTFT zone adjustments, they still overlap zones. One or more of your LTFT portions is always moving. They "collect garbage". During that time, the STFT is taking up up the slack for the base error AND the LTFT error on their own. Removal of one of the two variables that the STFT works against to maintain stoich isn't a bad thing. If the calibration has any rough spots in the VE or MAF, you can see how a block of fueling is not the appropriate correction.

Let's not forget that we are calibrating to 0% error, not a negative number. If the LTFTs wander a little positive, they will lock in during heavy throttle and offset WOT fueling. Adding fueling once tuned costs you a little power. Of course if they are negative when entering heavy throttle, they go to 0% and do nothing.

Once the VE and MAF (if used) are fully calibrated and smooth, the STFTs VERY easily take up the day to day slack and cover up issues like moderate IAT heat soak. That heat soak will drive LTFTs positive and again, affect WOT. That is of course bias error, but it plays a much smaller role at heavy airflow/throttle. The STFTs are free to wander positive a bit if they need and they will never affect WOT like LTFTs.

**pajeff02** · 08-29-2010, 05:21 PM

Thanks for the explanation Steve. There is just so much to tuning these cars. Seems overwhelming at times trying to get a handle on all of it.

**shady milkman** · 09-02-2010, 04:40 AM

Originally Posted by pajeff02

Thanks for the explanation Steve. There is just so much to tuning these cars. Seems overwhelming at times trying to get a handle on all of it.

x2 ..i just got my hp tuners yesterday and i have been looking over the tune Steve gave me ...looking at stuff and doing a lot of reading ...it is incredibly overwhelming at times when you realize how intertwined everything is

**pajeff02** · 09-02-2010, 08:14 AM

Originally Posted by shady milkman

x2 ..i just got my hp tuners yesterday and i have been looking over the tune Steve gave me ...looking at stuff and doing a lot of reading ...it is incredibly overwhelming at times when you realize how intertwined everything is

Have you joined the HP Tuners forum yet? I have learned quite a bit there -- especially from their video demos.

**shady milkman** · 09-02-2010, 09:05 AM

Originally Posted by pajeff02

Have you joined the HP Tuners forum yet? I have learned quite a bit there -- especially from their video demos.

i am reading up as much as i can ..l am reading a artical on VE tuning using fuel trims i found on tech.

i am realizing i need to invest in a WB BAD!

**shady milkman** · 09-02-2010, 09:06 AM

i think this weekend i am really going to focus on the scanner/histogram part of the suite

**Frost** · 09-02-2010, 10:57 AM

I'm working on a private forum for the people that buy HPTuner's from me that will be attached to my website. It will contain cfg files for all of the different year cars and trucks for everything from idle tuning, to MAF, VE, etc, as well as a how to on filtering data and how to avoid the largest of the entry level errors (such as copying a giant chunk of logged data and pasting it at once) and how to spot them at a glance. The board will have example files with injector data for popular injectors and more. I will have some example tunes and other tools/files in there as well.