Normally aspirated SCT, A/F, and fuel trims

[BrianT]

Is there anyone out there who has an NA SCT tuned vehicle and has actually looked at your A/F ratio, and OBDII fuel trims? Not should or could, but actually looked at what is happening.
If so, how was it tuned? Using A/F and RPM from a dyno or datalogger?
I have an SCT tuner, OBDII scanners, and an LM-1 setup and have read all the threads about SCT and have heard all of the hype/theory, but from my experience I would like to see if anyone has really looked at what their tune is actually doing to their A/F and fuel trims, I don't care about any seat of the pants opinions.
I keep hearing about these trucks where it worked great, but have yet to see any really concrete info after the tune.
I have seen a couple of dyno gains, no A/F or fuel trim info, also at least one 1/8th mile gain, but again no idea whether their running pig rich or lean as hell.

[bad360rt]

Very good question, I'm interested to see others results as well, since I'll be having my new setup tuned within the next month. Mine will be tuned on the dyno.

[meangreen]

I raised my my WOT AFR easily with the SCT PRP. I started a thread on dd called SCT dumbass where I posted some before and after datalogs with before and after fuel tables, so you can see how you can change pulsewidths in the software and how it affects AFR. I stopped posting on the thread becuase my PCM got fried, but I got it back now, and I will do the same with an F/I tune soon.

Fuel trims are only relevant in closed loop, and my part throttle fuel trims are always around -5%, so no tuning was needed at PT.

It's pretty easy to do. In the LM-1 software it will tell you how much to multiply your pulsewidths by to get a perfect AFR .... it's cool.

I also had tried an e-mail tune. I dyno'd it, and when I went to switch to my stock tune (tom fox), and my homebrew tune, for A/B/C comparisons, my PCM died ... on the above ground dyno .... lol.

But I will say that the TOM FOX felt stronger than my e-mailed tune which only dyno'd 240rwhp on a heads/cam/m1/5.2l..... The e-mail tune was a lean 14 AFR at peak HP. I wonder if I could have got a few more ponies at 12.5 AFR.

Shoot me an PM if you have any questions.

[BrianT]

I'm interested in fuel trims, because they apply at idle (closed loop), and my fuel trims and LM-1 A/F ratios aren't matching.
I'm just wondering what other people are seeing.
I've been having a terrible time trying to get an SCT tune right. I'm just wondering if we are using the right information to tune from.

[meangreen]

Fuel trims and AFR are two seperate but related things. In closed loop your AFR will always be 14.7. The fuel trims are how much fuel the PCM needs to pull or add to get to the 14.7 number. In theory a perfect tune would have 0 fuel trim. If you have the PRP, you can use fuel trims to dial in. For instance, say that at idle your fuel trims are -30%. you can go into the tables, multiply your current idle pulsewidth by .70 and you shoul then have fuel trims that are neer 0.

If in closed loop your LM-1 says anything but 14.7, you have mechanical problems ..... most likey O2 sensor or injectors

[meangreen]

An important point is that closed-loop AFR is not changeable. If you want an AFR other than 14.7, you need to run open-loop at all times. This can be easily done in the sofware by changing the minimunm TPS for open loop or a whole host of other ways.

At least this is my understanding .... I may be wrong, but I did stay at a Holiday Inn Express last night:jester:

I also had a hard time via e-mail. Much easier to write my own tunes.....

[BrianT]

Closed loop is not hardcoded to 14.7:1.
I've run everything from 10:1 to 21:1, closed loop. I can go home right now, start it up and when and if it goes closed loop, it will not be at 14.7:1.
Your PCM may try and keep it at 14.7:1 closed loop, but it is going to depend completely on how much fuel it has too add or pull.
And there are NO mechanical problems. It's all in the tune, or lack thereof.

[meangreen]

Closed loop is not hardcoded to 14.7:1.
I've run everything from 10:1 to 21:1, closed loop. I can go home right now, start it up and when and if it goes closed loop, it will not be at 14.7:1.
Your PCM may try and keep it at 14.7:1 closed loop, but it is going to depend completely on how much fuel it has too add or pull.
And there are NO mechanical problems. It's all in the tune, or lack thereof.

OK .... maybe i am wrong. What is your Idle AFR when warm. What are the idle LTFT and STFT when warm?

[BrianT]

Well, it depends on what tune I have in it.
Right now it must be rich enough that after it's warmed up good, 190, my bank1 will go closed loop, with STFTRM of around -30 and bank2 toggles in and out of open/closed loop, so I don't get a STFTRM. Of course I'm only on my 40th or so SCT tune so I'm still searching for them golden numbers.

[meangreen]

How are you reading ODB-II data? How does the stock tune work, in terms of AFR and Fuel trims. What is your AFR when you have a -30% fuel trim.

you've already lost me. i only have long-term and short-term fuel trims. no bank one or bank two.

[BrianT]

I have 3 OBDII scanners available, from a cheap $150.00 Actron, to a Cornwell and a Chrysler DRBIII. Of course the DRBIII gives by far the most info and lets you set things, but the Actron and Cornwell both do a good job of just reading the OBDII data. All of these show Short term and long term by banks.
The A/F when only one bank goes closed really doesn't matter, because I know the other bank is trying to compensate, but I don't know how much.
I just put another tune on it, and ended up with STFTRMs about -12 to -19 and my A/F was, at idle, from 12-18:1, mostly around 16:1. Cruise A/F @2500rpm is about 14.5:1. I haven't messed with WOT, yet.

[meangreen]

Wow. Sorry I can't be of help dude, but maybe someone else will chime in. I know that on my truck AFR is rock solid at 14.7 at idle and cruise unless I really make HUGE changes in the tables to where the PCM can't add/pull enough fuel to compensate for the wild commanded value. 12-16 is crazy!!

My PCM doen't even have the ability to read multiple banks.

This is a JTEC 5.2l/5.9l? If you don't mind me asking, what is your PCM# I would love to look at your tables as your truck seems totally different than mine...

[BrianT]

It's a '99 5.9L, 56040145AE.
Thanks for your responses, but I'm not really asking for help, more like I want to see what people's numbers are like when they have what they think is a really good tune.
And it's bank1 and bank2 on the engine.

[meangreen]

It's a '99 5.9L, 56040145AE.
Thanks for your responses, but I'm not really asking for help, more like I want to see what people's numbers are like when they have what they think is a really good tune.
And it's bank1 and bank2 on the engine.


OK. My guess is that you won't get many responses, as there aren't many DIY tuners who post the boards. Mostly guys who get dynotuned or e-mail tuned without logging.

Thanks for the PCM#. It's always cool to look at other Stock tunes. Your scalars are pretty differnet than mine...I didn't even realize that some dakotas have an O2 sensor for each bank ... lol ....

[grapejuice1998]

I have 3 OBDII scanners available, from a cheap $150.00 Actron, to a Cornwell and a Chrysler DRBIII. Of course the DRBIII gives by far the most info and lets you set things, but the Actron and Cornwell both do a good job of just reading the OBDII data. All of these show Short term and long term by banks.
The A/F when only one bank goes closed really doesn't matter, because I know the other bank is trying to compensate, but I don't know how much.
I just put another tune on it, and ended up with STFTRMs about -12 to -19 and my A/F was, at idle, from 12-18:1, mostly around 16:1. Cruise A/F @2500rpm is about 14.5:1. I haven't messed with WOT, yet.

So are you selling the DRB III?

[BrianT]

No, it's the dealership's. My son just brings it home when we need it.