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Reading on the MAF-T Discussion thread,
http://www.club3g.com/forum/showthread.php?p=1336264

I ran across jbasol's post:
jbasol said:
...I keep a pretty close eye on my tune of late. Mainly because of Rulez' unfortunate incident with his motor. Everyone should do the same (not that I think it was the tune that killed his motor, it just amde me realize I was being too lax in monitoring mine). One tidbit of information that I haven't mentioned yet is that our ECUs use the high fuel trim in conjunction with open loop. Perhaps I'm opening up a discussion that should be in a seperate post, perhaps everyone already knows this, and I'm just a slow learner. My point is that whatever you use to tune, keep a close eye on the high fuel trim. If you tune the car for an 11:1 AF while your high fuel trim is 0%, then drive around a few days and your high fuel trim goes to -20%, that could push you pretty far off your 11:1 AF target. Understand that the ECU does not run O2 feedback in open loop, and it does not update the high fuel trim with info obtained from open loop (becaus eit doesn't gather any O2 feedback during openloop), but it does believe that if during high rate cruise the fuel system requires some adjustment (the high fuel trim), it assumes this adjustment is also needed at WOT. The fuel trims are intended to assist in maintaining correct A/F even with things like dirty injectors, weakening fuel pump, etc... The designers figured these things don't magically fix themselves at WOT, so probably best to play it safe and program the ECU to use the igh trim at WOT as well. I'm guessing this is what RIPP always referred to as the reason the ECU was so tough to tune.

So put as much effort into your part throttle tuning as your WOT tuning. Keep those trims low and consistant and you will have a tune that will keep your car happy!

-John
So I decided to hook up my OBDII reader + ELMScanner:
http://www.qcontinuum.org/obdgauge/

And there are actually 2 short term and 2 long term fuel trims that come up. Are the 2 sort/long term items the same (duplicate short and long term trims), or are those 4 seperate variables?

So what is a safe range? Does this affect me only at WOT or for all throttle conditions?

So far, my A/F ratios have been pretty stable at ~11.7 at WOT. I'm still running on the base tune.

FYI, I did recently reset the ECU last week, as the battery was disconnected to do some electrical system work. It was pretty cool to watch the ECU adjust the A/F ratio while the car idled.
 

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you need to read a good book on OBD2 trims and stuff

here are the cliff notes:

STFT is a variable trim of +/- 30. LTFT is +/- 14. Long term is just that, take a long time to learn in and is based directly off STFT routine. If say your car on the first X starts/minutes was always -10 trim, the LTFT will begin to remember the car always is trying to lean out some and will begin to automatically use -5 lets say from now on. a STFT of -10 and a LTFT of -5 equals a -15 as well. this means the ecu is triming 15 points off of fuel for that given RPM.

Most people get into trouble with -14 LTFTs PLUS having NEGATIVE STFT's. This means your car is subtractin alot of fuel even up on top at WOT. the longer you drive the car, the more the trims change.

If you run a piggyback of ANY kind, you MUST run your car on a break in cycle. RIPP use to recommend their "500 mile learn in" for just this reason. They knew your fuel trims would equalize out after that point to be safe for use with the box tune. Everytime you reset the trims, you'll have to relearn them back in, regardless of the piggyback u run. one needs to check up on the trims as well often to ensrue the ECU isnt doing something retarded and leaning u out so far then on your next WO run u detonate without expecting it.

So how do u avoid getting the dreaded negative trims? dont be so rich. if you are seeing high negative #s u need to scale back fuel with the piggyback. tweaking fuel pressure is another game you can play. i dropped mine down to about 33psi to help a lil. a reasonable LTFT seems to be like -5 to -7 with 440cc injectors.
 

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TheFranchise said:
you need to read a good book on OBD2 trims and stuff

here are the cliff notes:

STFT is a variable trim of +/- 30. LTFT is +/- 14. Long term is just that, take a long time to learn in and is based directly off STFT routine. If say your car on the first X starts/minutes was always -10 trim, the LTFT will begin to remember the car always is trying to lean out some and will begin to automatically use -5 lets say from now on. a STFT of -10 and a LTFT of -5 equals a -15 as well. this means the ecu is triming 15 points off of fuel for that given RPM.

Most people get into trouble with -14 LTFTs PLUS having NEGATIVE STFT's. This means your car is subtractin alot of fuel even up on top at WOT. the longer you drive the car, the more the trims change.

If you run a piggyback of ANY kind, you MUST run your car on a break in cycle. RIPP use to recommend their "500 mile learn in" for just this reason. They knew your fuel trims would equalize out after that point to be safe for use with the box tune. Everytime you reset the trims, you'll have to relearn them back in, regardless of the piggyback u run. one needs to check up on the trims as well often to ensrue the ECU isnt doing something retarded and leaning u out so far then on your next WO run u detonate without expecting it.

So how do u avoid getting the dreaded negative trims? dont be so rich. if you are seeing high negative #s u need to scale back fuel with the piggyback. tweaking fuel pressure is another game you can play. i dropped mine down to about 33psi to help a lil. a reasonable LTFT seems to be like -5 to -7 with 440cc injectors.

Wow, that is interesting and good to know. I've been doing some datalog in closed loop operation so I can get those trims close to zero. I haven't really paid attention to them at WOT since I always believed that since the o2s were out of play, the ECU would just use the pre-determined open loop map(s). I always thought that is why our car will get very rich at the top, because Mits was just trying to protect the engine under extreme n/a opertation.

I'll have to do some WOT runs and see what the STFTs do. I'll get back if I find out something odd.
 

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repforenzo said:
Wow, that is interesting and good to know. I've been doing some datalog in closed loop operation so I can get those trims close to zero. I haven't really paid attention to them at WOT since I always believed that since the o2s were out of play, the ECU would just use the pre-determined open loop map(s). I always thought that is why our car will get very rich at the top, because Mits was just trying to protect the engine under extreme n/a opertation.

I'll have to do some WOT runs and see what the STFTs do. I'll get back if I find out something odd.
wot generally plays off the O2s but these cars definitly carry over some logic of LTFT to that map. a big place where many cars detonate up is that 75%ish throttle making a some boost and the car goes dead lean. its like a gray area of tuning finding those places of closed loop mode yet under boost and load.
 
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