Okay I've seen a lot of questions about LTrims and 02's so I'll try and help you understand it some what <img src="images/icons/wink.gif" border="0">

LTrims - LTrims Mean Nothing At WOT.
Now having said that let's get started. The goal here is to get your LTrims as close to 0 as possible using a MAFT. Using Autotap, create a log file of normal cruising of at least 50KB in size (the larger the file the easier to tune with). Once you have a good log file export it into excel and sort out the data. What we are looking for here are the LTrims when they are in fuel cells 1-19 only, all the rest of the data can be trashed. Once you have only the LTrims data that falls within fuel cells 1-19, take a average of these readings. This average will tell you if you are running rich (- neg. number) or lean (+ pos. number). Adjust your MAFT BASE for either a rich or a lean condition. Don't try and adjust it all out at once, in other words if your number is +14, don't adjust the MAFT Base to 15%, start with 5% and work you way up until your LTrims are as close to 0 as you can get them with little to no knock. Most cars run fine with them around +3. This is going to take several runs making atap log files.

Now once you have the LTrims dialed in lets move to the 02's and WOT setting on the MAFT. Same as above, make a atap log file but this time you will be interested in only the numbers for the 02's that fall in fuel cell 22 and when the throttle position is at 100%. After you have made a good sized atap log file, import it into excel and sort the data. Now all you are interested in is taking the numbers for the 02's that are in fuel cell 22 and 100% throttle, get a average of these. The ideal range for these are .89 - .91, anything above .91 is rich and anything below .89 is lean. Now to the MAFT, adjust the WOT setting according to if you are rich (adjust MAFT to -2) or lean (adjust MAFT to +2). After adjusting the MAFT, make another run logging it and repeat the above steps until your 02's read between .89-.91 and you have little to no knock.


Remember, one step at a time. There's a lot more to this than what I've written here. If you have any questions or need help, I'll be glad to answer any questions or help out. There's also a good write-up on this here LTFT / O2 Analysis & Tuning Guide

Anyone want to add to this I welcome it <img src="graemlins/fluffy.gif" border="0" alt="[Fluffy]" />

[ November 14, 2001: Message edited by: Rob98Z ]</p>

 

Here what I did with my MAFT as I don't have Atap.

Dyno with the MAFT at 0 and get a baseline.

Dyno again with the WOT leaned 2% and see if the power goes up. Each additional dyno pull out by 2% on the WOT setting until the power drops. When power drops back off 1 setting.

While not the ideal way, this method did get my car 6 rwhp & 6rwtq on the dyno with the MAFT.

 

Thats what I'm planning on doing...

I'm going to make 1 run at 0 then the next at 2% lean...

I will see what happens..

 

Rob98Z.. thanks for the reply to my thread and for this excellect write up. I will be having a major tuning session tommorow.. so I know who to turn to if I have any questions. Thanks Again.
Sean


BTW.. i see that you are in GA.. do u frequent any tracks in the season?

Sean

 

Sean np glad to help <img src="images/icons/wink.gif" border="0">

I'm at SDR just about every Friday night although I haven't gone in a few weeks, but will be going this Friday night being that it's the last night they will be open this season.

 

Cool.. I will most likely go as well. Although there is no point, my tires are holding me back from 12's.. <img src="images/icons/frown.gif" border="0"> But maybe if i can get this tuning worked out, i could ****** one! Dunno, I might be there.. Just say hey if u see a black 2000 Z28 with a Ultra Z hood. Late
<img src="graemlins/burnout.gif" border="0" alt="[Burnout]" />

Sean

 

I'd add that if you're running higher compression than stock or messing with a dry shot, you are better off with your WOT O2s being slightly on the rich side to avoid detonation.

A4 guys: LTRIMs can effect lock-up. If you're having lock-up problems with a cam, this is an area to explore.

 

[quote]Originally posted by Rob98Z:
<strong>Okay I've seen a lot of questions about LTrims and 02's so I'll try and help you understand it some what <img src="images/icons/wink.gif" border="0">

LTrims - LTrims Mean Nothing At WOT.
Now having said that let's get started. The goal here is to get your LTrims as close to 0 as possible using a MAFT. Using Autotap, create a log file of normal cruising of at least 50KB in size (the larger the file the easier to tune with). Once you have a good log file export it into excel and sort out the data. What we are looking for here are the LTrims when they are in fuel cells 1-19 only, all the rest of the data can be trashed. Once you have only the LTrims data that falls within fuel cells 1-19, take a average of these readings. This average will tell you if you are running rich (- neg. number) or lean (+ pos. number). Adjust your MAFT BASE for either a rich or a lean condition. Don't try and adjust it all out at once, in other words if your number is +14, don't adjust the MAFT Base to 15%, start with 5% and work you way up until your LTrims are as close to 0 as you can get them with little to no knock. Most cars run fine with them around +3. This is going to take several runs making atap log files.

Now once you have the LTrims dialed in lets move to the 02's and WOT setting on the MAFT. Same as above, make a atap log file but this time you will be interested in only the numbers for the 02's that fall in fuel cell 22 and when the throttle position is at 100%. After you have made a good sized atap log file, import it into excel and sort the data. Now all you are interested in is taking the numbers for the 02's that are in fuel cell 22 and 100% throttle, get a average of these. The ideal range for these are .89 - .91, anything above .91 is rich and anything below .89 is lean. Now to the MAFT, adjust the WOT setting according to if you are rich (adjust MAFT to -2) or lean (adjust MAFT to +2). After adjusting the MAFT, make another run logging it and repeat the above steps until your 02's read between .89-.91 and you have little to no knock.


Remember, one step at a time. There's a lot more to this than what I've written here. If you have any questions or need help, I'll be glad to answer any questions or help out. There's also a good write-up on this here LTFT / O2 Analysis & Tuning Guide

Anyone want to add to this I welcome it <img src="graemlins/fluffy.gif" border="0" alt="[Fluffy]" />

[ November 14, 2001: Message edited by: Rob98Z ]</strong><hr></blockquote>


Let me see if I understand this correctly. I did an autotap run today. I just finished getting the LTFT's in cells 1-19. The average of LTFT B1 is 5.26 and the average of LTFT B2 is 4.06. Now do I ad these averages together and get 9.32 and then assume the car is running lean, therefore I need to adjust a maft for a lean condition and try to get it as close to 0 as possible, or am I working with both sets of numbers and am trying to get both number's as close to zero as possible. Is my thinking correct?

 

Yes there is a lean condition. On the MAFT set the base for 5% rich leave the WOT setting alone for now. Drive around some collect more Autotap data and see how the LTFT looks. I gave the car 50 – 100 miles after each change to “normalize”.

You can average LTFT B1 and B2 to get an overall condition.

Adding them together does nothing for you with the exception of it being the first step to averaging them! <img src="images/icons/wink.gif" border="0">

 

I am still running lean after installing Mac header's w/orp and I thought it would richen my car up A little but I still get pinging when using nitrous on the top of 3rd and in 4th gear?
So what setting on the maf trans would richen my car just A little?

 

[quote]Originally posted by WICKED SS:
<strong>I am still running lean after installing Mac header's w/orp and I thought it would richen my car up A little?</strong><hr></blockquote>
Where'd you get the idea that would richen your car up? Headers will lean out your car because of the increased air flow.
[quote]<strong>but I still get pinging when using nitrous on the top of 3rd and in 4th gear?
So what setting on the maf trans would richen my car just A little?</strong><hr></blockquote>


Assuming that you got information from autotap that indicated that you are running lean at WOT then you would need to increase your WOT setting 2% at a time until you get your 02's reading between .91-.87. and autotap again and get a average reading of your 02's.

 

[quote]Originally posted by Rob98Z:
<strong>
Where'd you get the idea that would richen your car up? Headers will lean out your car because of the increased air flow.
</strong><hr></blockquote>

A number of people have reported that after adding headers they ran rich.

 

What if I'm running O2 Simm (I am) how will this factor into the math?

 

Your O2 simms are after the cats. These are not the O2 readings you want to look at- look at the pre-cat O2 readings.

 

With ODBII the o2 sensors pick up that there is a leaner exhaust mixture and then add fuel to compensate creating a rich condition.

 

[quote]Originally posted by BADSS:
<strong>Your O2 simms are after the cats. These are not the O2 readings you want to look at- look at the pre-cat O2 readings.</strong><hr></blockquote>

I have no Cats on my car and the O2 sims are in the SLP LT Headers just before the Y pipe.

[ November 23, 2001: Message edited by: 2000 Camaro SS ]</p>

 

Even with out the cats the car still uses the front two O2 sensors to help determine if it is rich or lean.

 

Mike's got it right- even w/o cats, you have front and rear O2 sensors, and you should be running the simms in place of the rear O2's. The front O2's are the ones the PCM looks at to adjust your A/F ratio. The simms just trick the PCM into thinking you have cats and that they are functioning properly. Rear O2's are only for emissions compliance- they do not affect the performance of the car.

 

You dont add the left and right banks to get a total LTRIM. If you have 8% left bank and right bank you have 8% Ltrims <img src="images/icons/smile.gif" border="0">
Generally on the dyno LTRIMS in the 8-12% range (EACH bank) make about 6-8RWHP more while keeping a safe AF ratio. Every car is different. My car for example always ran faster with the stock descreened MAF and stock program. The best way to do it is to see what gives you the max timing and the least amount of knock retard. If you are seeing 4% Ltrims you are fine, nothing to worry about.
Hope this helps,
Chris

 

Let me if this little formula will clear it up a little.

LTFT B1 + LTFT B2 = X
X / 2 = average LTFT

02 B1S1 + 02 B2S1 = X
X / 2 = average 02's