Difference in LTFTs
Difference in LTFTs This is one of those times where I really wish I had purchased HP Tuners and not a Predator... Car in question is in my sig. I recently changed out my driver side upstream O2 (rear O2s are not there and tuned out) as it was throwing code P0135. I hadn't really hooked up the Predator and taken a good look at it since the LS6 intake went on so I'm sure the tune has been in need of some tweaking since then. So after driving it for about a day after the new O2, I hooked up the Predator and noticed that my LTFTs were rather high when cruising around, like anywhere from 9.38% to 24%, but both banks were reading relatively the same (within 1% of each other). I assume those numbers are due to the LS6 intake. I got out on the highway and did some WOT spells with it and noticed that bank 1 is 9.38% and bank 2 is 1.58% steadily. The mV on the O2s are about 960 in bank 1 and 930 in bank 2. Unfortunately, I can only see LTFTs OR mV since they are pretty far apart on the list of parameters on the Predator, but those are the numbers I was getting on multiple WOT runs. What's with the difference from bank to bank only at WOT? I know I need to dial in the LTFTs a little better, but do I care about the 8% difference since these are only narrowband O2s? I plan on getting the car a real tune in the upcoming months, maybe around tax return time, so I'm just not sure how much fussing I should do with the Predator right now since all seems well except for this little bank to bank discrepancy and some recent drop in gas mileage (from 18 mpg to 15 mpg), but it is winter. Any advice?
TECH Enthusiast
Joined: Aug 2006
Posts: 502
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You changed out an O2 sensor.
This isn't abnormal. The computer had LTFT's set based on what the old sensor was feeding it. You now have different data coming in from the new sensor and the computer now has to change the LTFT's based on what that sensor is reading.
You really should have changed both at the same time. O2 sensors response times get slower as they age and they should be replaced in pairs.
Given the new sensor and an intake change, you will see some LTFT changes and the difference will vary greatly from one bank to the other since you changed one bank and not the other (especially if that old sensor you changed out was sending data that was way off).
Change the other sensor, reset your fuel trims, come back and let us know what you get after about 100 miles.
This isn't abnormal. The computer had LTFT's set based on what the old sensor was feeding it. You now have different data coming in from the new sensor and the computer now has to change the LTFT's based on what that sensor is reading.
You really should have changed both at the same time. O2 sensors response times get slower as they age and they should be replaced in pairs.
Given the new sensor and an intake change, you will see some LTFT changes and the difference will vary greatly from one bank to the other since you changed one bank and not the other (especially if that old sensor you changed out was sending data that was way off).
Change the other sensor, reset your fuel trims, come back and let us know what you get after about 100 miles.
Actually,the way your car is tuned it actually lives off those narrowband sensors.Thats a big swing between the 2 and can definitely affect the tune.
First I'd look for exhaust leaks near the sensors,then intake leaks.
First I'd look for exhaust leaks near the sensors,then intake leaks.
Daily driving you are going to have issues. Do as Dan Stewart recommended. Just FYI. At WOT your O2's will flatten out. I would say they look equal imo. There is no jumping around or movement in them when at WOT when I am using the Hp Tuners scanner software. Your O2's are also not used at WOT by the way.
