LTFT's

Wizeguy28 · Post by **Wizeguy28** » Tue Feb 26, 2008 5:47 pm

Ok, I'm going to admit I have NO idea what an LTFT's is.

I have a predator on the way, and I would just like to know what LTFT's are all about. Thanks guys.

Post by **06MonteSS** » Tue Feb 26, 2008 6:59 pm

fuel trims are a correction factor applied to the base fueling map the engine uses... the Long Term Fuel Trims are used by your vehicles ECM to control the fueling / air fuel ratio to the engine...

if your car is running lean, you will have positive fuel trims, which indicates that the ECM is adding fuel to get to and maintain the stoich AFR value of 14.75 during normal driving/cruise.

if your car is running rich, you will have negative fuel trims, which indicates that the ECM is subtracting fuel to get down to and maintain the stoich AFR value of 14.75 during normal driving/cruise.

the fuel trims are not used during WOT runs, as there is a separate PE (power enrichment) table in the ECM that it uses for the WOT fueling. BUT - an exception to this rule is if you have positive fuel trims going into and during WOT... this tells the ECM that you were running lean before you went WOT, so it assumes that you are still lean during WOT so it then adds that additional fuel on top of the PE fueling table that it's already using for its info on how much fuel to spray at WOT.

this is why you want to monitor your LTFT's during normal driving/cruising to see what they are at... so then you can adjust your injector slope to get your ltft's in the 0 to -2 range - this is so no additional fuel is being added when going WOT. and it also makes all of your fueling much more predictable and easier to tune for at WOT.

However, your older model predator for your truck can not save logs, so you will need to watch the data live on the predator's screen as you drive... have someone ride with ya to write down numbers if you need to.

now...

adjusting the injector slope negative makes your fuel injectors spray more fuel...

adjusting the injector slope positive makes your fuel injectors spray less fuel...

so for example, if your average ltft's at normal cruise were 2.34, then you would adjust your injector slope to -3%.... this would effectively make your average ltft's now be at -0.66 - perfect!

if your ltft's were -2.34, you would adjust your slope to be +2%.... this would effectively make your average ltft's now be at -0.34 - perfect!

so that sums it up in a nutshell...

oldgoatgoesnew · Post by **oldgoatgoesnew** » Wed Feb 27, 2008 12:46 am

Lew, you quite articulate and your choice of words and mastery over the visual basic language (DSlogRedux) imply that you have technical background. Are you a ME? Anyway, your explanation is clear, short and to the point. It's nice to have you on this forum. I was wondering (after softening you up a bit) if you had a chance to look at my log data and had some recommendations. I hope that I am not being too forward. You have given great advice to people in this forum. I realize you do as curtious, not for pay, and kindred spirit - like to tweak engines and fast GM cars. If you have any pointers, I would greatly appreciated it. P.S. I am not one of tools that will throw it back in face, like Mr. what the hell.

Wizeguy28 · Post by **Wizeguy28** » Wed Feb 27, 2008 9:16 am

Wow. That explains it all. I have to agree with the above post. I'm real impressed with your knowledge. I'm attending the University of Northwestern Ohio, in Lima, so I'm still in the process of learning all this.

Its definitly confusing at first how all the numbers are kind of backwards if you know what I'm talking about. "if your car is running lean, you will have positive fuel trims, which indicates that the ECM is adding fuel to get to and maintain the stoich AFR value of 14.75 during normal driving/cruise." You would think (or at least I would) that if your vehicle was running lean it would be running negative numbers, or if you vehicle is running rich it would be positive numbers.

so for example, if your average ltft's at normal cruise were 2.34, then you would adjust your injector slope to -3%.... this would effectively make your average ltft's now be at -0.66 - perfect!

if your ltft's were -2.34, you would adjust your slope to be +2%.... this would effectively make your average ltft's now be at -0.34 - perfect!

So is the goal here to get it as close to 0 as possible? I think I read somewhere that is the goal.

Thanks for all your help bud. You may hear from me again down the road, haha

Luke

Post by **06MonteSS** » Wed Feb 27, 2008 9:20 am

oldgoatgoesnew:

-- nah, 1st5.7GTO (Mr. what the hell hahaha) is not a tool.. he was just concerned about his car and something being wrong with it since he didn't understand something, and wasn't in the mood for joking around at the time... understandable... no biggie... he's a good guy...

thanks man... thanks for the kind words... yeah, saw your other post with your log - just been swamped at work here... will get to it in a bit...

not an ME, but am technical... been doing computer work for YEARS... build my own systems, etc etc... my normal job is being a senior web/internet developer.... and I have to say, that the VB app (DSLogredux) I helped to develop, I contributed my knowledge/experience on all the parameter info, readings, data, etc etc to another great guy on here (GrumpyAeroGuy) - he's the one that does the actual VB programming...

so once I got the predator for my car just over a year ago, I dove right into the deep end - finding out all I could - afterall, it was dealing with the car's COMPUTER...

anyway, will check your log and reply over there...

thx man!
-Lew

Post by **06MonteSS** » Wed Feb 27, 2008 9:42 am

Hey Wizeguy...

yes, you want to be as close to 0 as possible, or a little negative - so that no fuel gets added when at WOT... hence the 0 to -2 range for the ltft's...

Wizeguy28 · Post by **Wizeguy28** » Wed Feb 27, 2008 9:56 am

Alright man, sounds good. Thanks

1st6.0GTO · Post by **1st6.0GTO** » Wed Feb 27, 2008 8:58 pm

[quote="oldgoatgoesnew"]Lew, you quite articulate and your choice of words and mastery over the visual basic language (DSlogRedux) imply that you have technical background. Are you a ME? Anyway, your explanation is clear, short and to the point. It's nice to have you on this forum. I was wondering (after softening you up a bit) if you had a chance to look at my log data and had some recommendations. I hope that I am not being too forward. You have given great advice to people in this forum. I realize you do as curtious, not for pay, and kindred spirit - like to tweak engines and fast GM cars. If you have any pointers, I would greatly appreciated it. P.S. I am not one of tools that will throw it back in face, like Mr. what the hell. [/quote]

As Lew said I was concerned about the operation of my car, due to a sudden change in the LTFT. Since this is the 4th Pred I have owned and up till last friday, never saw the trims revert to the + like they did. I have done quite a bit of tuning of all 4 cars I have owned with the 4 different pred's. And after only getting one response from Johan about reset and redo I wasnt real happy about the lack of more info. And since it took some stirring up things to get more of a response, well I apologized.

oldgoatgoesnew · Post by **oldgoatgoesnew** » Thu Feb 28, 2008 12:22 am

Hey 1st6.0gto no qualms here. How's your car doing? I know Iâ€™d be a little torqued if my car tanked. I understand, you paid a lot money and no support, but you have to admit these guys at Diablo are a lot better than most. At least, weâ€™re not talking to some clueless Indian tech half way around the world.

Hey, just trying to keep a friendly forum for those of us who like lots of HP!!!! From what Lew said, you sound like okay guy. Sorry, if I stepped over the line.

I do suggest some light reading to bring you one with your car, â€œZen and the Art of Motorcycle Maintenanceâ€

1st6.0GTO · Post by **1st6.0GTO** » Thu Feb 28, 2008 6:33 pm

Havent had a chance to do any data viewing the last few days, hoping to tomorrow. Things here in NE AL have warmed up, but tomorrow there is a chance of rain. As I said if I have to play with the numbers any it will be +/-1 at a time. I might just for the hell of it move the slope to -3 (from -4) and see how she runs. All I do know (which is weird) the car ran better in the + side of the LTFT, (but still 0 @ WOT) than it did while it was in the - side of the LTFT (also still 0 @ WOT). It eliminated my KR and gave me timing. SO I guess we will see, I know the ECM will return its self to 14.7 regardless over time, so it might be a waist of time to even bump it that 1%. Thanks for asking.
On a side note, yes I agree tech support is very good with DS and thanks to those out there with there advice.

sickREDsierra · Post by **sickREDsierra** » Thu Feb 28, 2008 6:40 pm

1st6.0GTO wrote:Havent had a chance to do any data viewing the last few days, hoping to tomorrow. Things here in NE AL have warmed up, but tomorrow there is a chance of rain. As I said if I have to play with the numbers any it will be +/-1 at a time. I might just for the hell of it move the slope to -3 (from -4) and see how she runs. All I do know (which is weird) the car ran better in the + side of the LTFT, (but still 0 @ WOT) than it did while it was in the - side of the LTFT (also still 0 @ WOT). It eliminated my KR and gave me timing. SO I guess we will see, I know the ECM will return its self to 14.7 regardless over time, so it might be a waist of time to even bump it that 1%. Thanks for asking.
On a side note, yes I agree tech support is very good with DS and thanks to those out there with there advice.

where you at in alabama? Roll Tide

1st6.0GTO · Post by **1st6.0GTO** » Thu Feb 28, 2008 9:13 pm

Huntsville area. Moved up here last April (wife and I) from Melbourne FL. My wife is from here and her famiily is all up here. I read your in the Mobile area. We have a small but loyal group of GTO's up here. Good group of friends, and with all this talk of tuning, we are planing a gtg for a dyno/tuning day up here soon.

sickREDsierra · Post by **sickREDsierra** » Fri Feb 29, 2008 9:02 am

sounds good man! i been through Huntsville a time or three, i just love it around the beach down here! stayed in Melbourne for a few weeks once also, then went and surfed on cocoa beach. very cool places.

good luck on that meet! make sure you post up those dynbo numbers for us when you go!

Wizeguy28 · Post by **Wizeguy28** » Fri Feb 29, 2008 10:03 pm

Alright, I hope i still have your attention monte. So I ran a cruise down the highway last night (after I ran the truck for a good 20-30 min to warm her up). I watched the LTFT's and the first one was at about 7.31 on average, and the other one was at about 8.34. I was running at about 55-60mph, 2000-2200 rpms in 3rd gear (4L60E). So after reading and trying to analyize all your pointers and tips, does this mean I'm running pretty damn lean? Does this mean I need to adjust the injector slope +7 or +8ish to get around 0? So if I was reading your write up correctly. When I'm running down the highway as I was last night, I want my LTFT's to read somewhere around -1 - 0? Thanks

Wizeguy28 · Post by **Wizeguy28** » Fri Feb 29, 2008 10:05 pm

Does this mean I need to adjust the injector slope +7 or +8ish to get around 0?

I meant -7 or -8.....right? lol

And If I'm correct with all of this. Are my LTFT's like this because of that Fram Boost Intake system?

LTFT's

LTFT's

RE: LTFT