Benz-O-Rama

Gents,

My logging software, like most, will log fuel trims. Mine logs as %, and are labeled SB1, SB2, LB1, and LB2. I assume that means:

Short term - Bank 1
Short term - Bank 2
Long term - Bank 1
Long term - Bank 2

So my questions are these:

1. What exactly is this data?
2. What is the proper procedure to collect this data?
3. Should I be interested in these numbers at idle, normal acceleration or WOT? Or all of them?
4. What's a red flag? What's considered good, what's considered bad?

I'm just not informed enough, to not ask. I'd rather appear dumb for not knowing, and educate myself here with your help, then pretend I know what I'm looking at and toast my V12TT.


The genesis of this, is because I feel I might be running a bit rich. I'm getting that sulfuric (bad cats) smell at cold startup, and after beating on her. I just want to make sure everything's ok with the fuel. My wideband will hopefully get installed this month, so that will give me more info to look at.


Thanks guys.

pbsis

This would be good info to have. Further more I know that we can log 02 volts. I seem to recall that these are like a less accurate wide band AFR. I think the higher the voltage the richer the car....or maybe its vice versa hahah! Someone Im sure knows the answers to these questions.

shardul

iTrader: (1)

BOR you are a veteran with aspects of tuning such as timing, fuel, watermarks on files etc etc you should know this by now. Tuners are very busy poeple so it is hard to get a hold of them hehehehe but I will try to explain it.

Basically LTFT are an average of STFT. They should be within +5 and -5 %. STFT represent the ECUs ability to add or subtract fuel via the help of the injectors.
If you use a regular american OBDII scanner on a Mercedes negative LTFT mean the ecu is adding fuel vice veresa. So for example you put bigger injector and your LTFT are negative that means the ECU is trying to add fuel and hence you need a tune to scale those injectors correctly. On all stock cars LTFT will be between -2 and + 2 %. Any time LTFT go beyoud -25 to +25 % the CEL will be triggerd with a lean or rich condition code on a particular bank.

Hope this Helps
I was just busting ***** on my first sentence. Hope no offense is taken

loungn14

ya what he said....oh and it usually takes a few days for the ltft to average correctly....

Benz-O-Rama

No offense at all. It's pretty impossible to offend me, trust me.

When you say "On all stock cars LTFT will be between -2 and + 2 %." Are speaking specifically about cars with stock injectors, or does this also encompass stock tunes?

What I gather from your statements above, is that if my LTFT runs in a deep negative, I'm running lean, and the ECU is attempting to add fuel. Deep positive, and I'm running rich, and the ECU is trying to pull fuel.

Yes?

shardul

iTrader: (1)

stock injectors and stock tunes.

see here is where it gets confusing, negative means the ecu is adding fuel but it doesnot necessarily mean you are running lean, but in most cases yes the car is a bit lean. i would double check the AFRs with a wideband.

KLR CLS

On My Torque or android logger, My LFTF were -20+% due to rich part throttle maps with the EC injectors, and was throwing Rich mixture codes. Jerry Leaned out the part throttle maps and I am back into the +/- 5% range.

Benz-O-Rama

Thanks guys. My LTFT stays between -1 and +1, so everything is probably ok there. I wonder if the smell is from the muffler delete. Ive been running no rear mufflers forever, but I've only recently noticed the smell since my last retune.

I think I need to log the STFT at cold start, since that is when it's most noticeable.

shardul

iTrader: (1)

BOR you are fine if they are between 1 percent. When you check the STFT they will change rapidly. If the change very slowly then that is a sign that your O2 sensors are going bad because they are not sampling fast enough.