Thread: Negative LTFT and resettting trims.

Discovered Long and Short term fuel trim monitoring, not logging just real time scanning I was getting LTFT -13ish idle, no better than -5 at WOT.
Reset the fuel trims and now getting -11 at idle, -7.5 at cruise and 0.0 at WOT which I think is better? STFT bounce seemingly random +/-2 but peg 0.0 at WOT also.

Still indicates I'm running rich right? With CAI and SDs I wouldn't think that would happen, so I'm thinking maybe I have a bad O2 sensor?

still not all that great but would be a lot better if you could get them down to 0 to -5

You shouldn't be that rich your trim should always zero out at wot because of open loop. At p.e enrich you'll see a rich indication anway.anway.until you get tuned your numbers won't get any closer.

What's p.e enrich? And after driving around some more I'm back to the worse looking trims, -5.4 at WOT. I see no other indicators of running rich though, which is why I wonder about the O2 sensors. Also picking up a lot more KR than I was stock. I initially assumed it's cause it's stupid cold out, but if I have an O2 sensor telling the PCM I'm falsely running rich, that would mean I'm actually leaning out by it pulling the trims?

Is there any tests or scans I can do to figure this out? I'd rather not just throw parts at it.

how old is your 02? and stop paying attention to trims at WOT, because they freeze anyway as soon as you reach enrichment which is whatever TPSxRPMXMAP you have set in your tune. 02MV's would be more useful but not the most accurate way to determine where your fueling is at. if you have a wideband you should utilize that to double check where youre really at.

Stock tune. O2 sensors were new in July.

S1B1 (front sensor?) is apparently reading completely random rapidly bouncing between 50mv and 900mv and any number between. No use saving the log it since it just looks like noise. The only repeatability is when I get on the throttle hard and then suddenly let off, readings go near 0 briefly before resuming the random readings.

S1B2 (after cat?) refreshes slowly but predictably, accelerating the numbers go up, coasting the mv goes down.

the front sensor should look the way you are describing. when you are WOT it should run around 950mv and stay there. trims can indeed lock in other than 0 at WOT if you tune is really ****ed. i guess the first thing that we should know is what are you using to log and do you have tuning abilities with it?

Not to nit-pick here but 950mv would be really rich, 900-920ish is normally around target afr from what I've always seen. Of course I used a wideband to make sure I was where I needed to be but never saw above .940mv even at 10.8 afr.

And as stated front o2 sensor must swing back and forth, it's ALWAYS trying to achive stoich during normal throttle operations.

Front sensor doesn't go over 900 that I've seen, doesn't peg out at WOT either but does bounce around at higher numbers. Using Aeroforce to live scan, AutoTap to log, and I have DHP but have zero experience with it.

dhp is cake to scan with. plug it into the car, then click the scantool a window opens, you pick what you want to scan from the left side, it will pop into the right side. then click scan. drive and then click disconnect iirc, it will save the file. then you go to export logs and save it from there, you want the cvc iirc file.

Originally Posted by Fivefingerdeathpunch

Not to nit-pick here but 950mv would be really rich, 900-920ish is normally around target afr from what I've always seen. Of course I used a wideband to make sure I was where I needed to be but never saw above .940mv even at 10.8 afr.

And as stated front o2 sensor must swing back and forth, it's ALWAYS trying to achive stoich during normal throttle operations.

it depends on the car/sensor actually. before i got my wideband i used the narrow's at 940-950 and it was about 11.2 in my car. they are tunreliable. basically shouldnt be tuning off them but live and learn. get a wideband...pay to play.

FWIW my buddy's car was more like yours around 920-930 to get to 11.0 to 1. thats why i dont use them anymore.

Originally Posted by industrialfish

Front sensor doesn't go over 900 that I've seen, doesn't peg out at WOT either but does bounce around at higher numbers. Using Aeroforce to live scan, AutoTap to log, and I have DHP but have zero experience with it.

use dhp to scan maf frequency, FT cell, and LTFT save the log. export as .CSV file. open in excel. filter data by FT cell. delete all lines with FTcell 3. paste data and your current maf table into the excel sheet and flash new maf curve to computer. reset fuel trims and repeat. when you log dont go into PE. get as high as you can into the MAF table hertz wise but dont get into PE. drive should be 30-40 minutes and should yield 10,000+ lines of data. maybe. its been a long time since i have done it this way since i have HPtuners now.