Short term fuel trim
Nov 9, 2007, 04:27 PM
#1
Short term fuel trim
I have noticed that by doing the following, I get noticeably more torque:
1) swap cat for straight pipe
2) reset ECU
3) drive for a day or two
4) replace test-pipe with cat
I don't like driving without a cat unless I'm at the track, but even with the cat put back in, the torque gains remain. If I reset the ECU again after putting the cat back on, the car looses torque. I'm guessing this is due to the short term fuel trim, which somehow is "learned" differently when I put the test pipe on and reset the ECU, but remains when I put the cat back on without a reset.
So, is there a way to "save" my ECU state after going through this, so that if I reset my battery with the cat on, I can just reload the short term fuel trim via ECUFlash to get the higher torque output? I wasn't sure if ECUFlash stores short term trim data or just the "base tune".
1) swap cat for straight pipe
2) reset ECU
3) drive for a day or two
4) replace test-pipe with cat
I don't like driving without a cat unless I'm at the track, but even with the cat put back in, the torque gains remain. If I reset the ECU again after putting the cat back on, the car looses torque. I'm guessing this is due to the short term fuel trim, which somehow is "learned" differently when I put the test pipe on and reset the ECU, but remains when I put the cat back on without a reset.
So, is there a way to "save" my ECU state after going through this, so that if I reset my battery with the cat on, I can just reload the short term fuel trim via ECUFlash to get the higher torque output? I wasn't sure if ECUFlash stores short term trim data or just the "base tune".
Nov 9, 2007, 05:21 PM
#2
It really shouldn't make a difference because the short term fuel trim is only telling you how much the ECU had to change the mixture (almost in an instant) to achieve the 14.7:1 AFR. The only way the AFR would change is if the difference was so great that it exceeded the ECU's ability to achieve a 14.7:1 AFR, which is roughly 50% between STFT and LTFT. If you have a wideband, you will notice that you are still cruising at 14.7:1 either way. Any high torque readings you can get is from open loop mapping which would be the exact same anyways.
If ANYTHING, you might get a good amount of carbon buildup with the cat installed and with the free-flowing testpipe it kind of purges some of the build-up (would create a greater scavenging effect). After a few days with the cat, the carbon build-up returns. This is a shot in the dark of course.
If ANYTHING, you might get a good amount of carbon buildup with the cat installed and with the free-flowing testpipe it kind of purges some of the build-up (would create a greater scavenging effect). After a few days with the cat, the carbon build-up returns. This is a shot in the dark of course.
Last edited by Jack_of_Trades; Nov 9, 2007 at 05:32 PM.
I'm going to try and log it, to see if there is really something going on, or if my butt-dyno is broken.
Nov 10, 2007, 07:59 AM
#5
It really shouldn't make a difference because the short term fuel trim is only telling you how much the ECU had to change the mixture (almost in an instant) to achieve the 14.7:1 AFR. The only way the AFR would change is if the difference was so great that it exceeded the ECU's ability to achieve a 14.7:1 AFR, which is roughly 50% between STFT and LTFT. If you have a wideband, you will notice that you are still cruising at 14.7:1 either way. Any high torque readings you can get is from open loop mapping which would be the exact same anyways.
If ANYTHING, you might get a good amount of carbon buildup with the cat installed and with the free-flowing testpipe it kind of purges some of the build-up (would create a greater scavenging effect). After a few days with the cat, the carbon build-up returns. This is a shot in the dark of course.
If ANYTHING, you might get a good amount of carbon buildup with the cat installed and with the free-flowing testpipe it kind of purges some of the build-up (would create a greater scavenging effect). After a few days with the cat, the carbon build-up returns. This is a shot in the dark of course.
Of course as far as cat/test pipe goes, I find it a little hard to believe that kept the same hp/tq. values when swapping the two around. It's pretty much law of physics...remove an obstruction and whatever is flowing through will flow better and faster, put it back in and it will slow it down again. I think your butt-dyno needs to be recalibrated lol
Nov 10, 2007, 10:29 AM
#7
I'm not sure I quite understand...after I installed my Injen IC piping and intake I reset the ecu to let it relearn the new parts. It took my '03 Evo 8 about 3 days to relearn the fuel trims. On day one my afr's at idle and cruising speed were all over the place and had a heck of a time trying to get to near that 14.7 mark. Most of the time it wanted to stay near 15.3-16 until you built up pressure or came under load. Day 2 was pretty similar but getting closer to where it needed to be, and by day 3 it was pretty good. Definitely wasn't an instantaneous adjustment.
Of course as far as cat/test pipe goes, I find it a little hard to believe that kept the same hp/tq. values when swapping the two around. It's pretty much law of physics...remove an obstruction and whatever is flowing through will flow better and faster, put it back in and it will slow it down again. I think your butt-dyno needs to be recalibrated lol
Of course as far as cat/test pipe goes, I find it a little hard to believe that kept the same hp/tq. values when swapping the two around. It's pretty much law of physics...remove an obstruction and whatever is flowing through will flow better and faster, put it back in and it will slow it down again. I think your butt-dyno needs to be recalibrated lol
Last edited by Jack_of_Trades; Nov 10, 2007 at 10:33 AM.
Trending Topics
Thread
Thread Starter
Forum
Replies
Last Post
ziad
Evo Engine / Turbo / Drivetrain
3
Jun 12, 2012 08:22 PM
