Input needed re:fuel trims in tune: datalog attached

[ManBearPig]

I have had a Lund tune on my stock 16 GT for a few years with no real concerns. I just put on a set of Texas Speed longtubes and I have read time and time again that Lund does not revise tunes for headers, but I can't really find why. I keep reading about headers being "baked in" the tune, but have no idea what that means. Does that mean that the PCM will learn errors in the MAF curve to account for additional airflow and transport delay?


I have started paying close attention to several pids and am questioning fuel trims. Unfortunately I never really paid much attention before so I don't have anything solid to compare to. After 100 miles, the car had learned the long term trims within 2-3% on both banks. After about 200 miles the long term trims are closer to 4-5% on average. Of course the trims vary under certain circumstances and conditions. WOT is actually pretty close to 0 but cruising is off more. I have seen the long term trims off as much as 7% but for the most part, I'm seeing 3-5%. Short term trims are always very close. They are almost always within 2%, and they are negative just as often as positive, so I think the long term has learned about as close as it can.


Lund wants $50 to review a datalog so I'm hoping I can get some insight as to whether or not what I'm seeing is acceptable? I don't mind paying for a tune revision but I don’t want to spend 50 bucks just to have them tell me "yep, you're good", which is what I suspect I would get.


The car is on a 93 tune, stock intake…stock everything else. It pulls hard and sees lots of timing under WOT. Throttle seems to be a bit touchier/herky-jerkier after the headers but that could just be in my head. It has never been as smooth as I'd like, even when the car (and tune) were stock.


Should I pony up for the datalog review or should I be happy with the fuel trims I'm seeing? What is an acceptable amount of error in a *good* tune?


Thanks

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[ENPhoto]

It's always best to tune for headers, even to just manually adjust the transport delay and transport time constant. If you are catless, tuners have the option of removing your Cat Overtemp Protection as well. (when in full throttle, COT protection will dump fuel to protect the cats. Stock from the factory, mine did this from 5200rpm and up while in 4th/5th gear when doing 3-5 gear pulls)

This thread on the hp forums might be informative, if you want to check it out:
https://forum.hptuners.com/showthread.php?63189-Transport-Delay-Transport-Time-Constant

For LTFT, when I tune I like to get to within 2-3% error while at different steady throttle positions in different gears.

I'm guessing that at initial quick throttle changes, during abrupt DFCO (deceleration), aggressive tip-in and gear changes you are seeing upwards of 7% LTFT? Sometimes when I was logging steady state, I'd be at a certain throttle position to hit a "cell" and I'd do a weird throttle/gear change (like 6th to 4th with minimal throttle applied and it would skew/alter my results in new cell that I landed in)

As long as when you are cruising at steady throttle in different positions, and it's within that 2-3%, you should be fine. I don't know how Lund does it, they might just log it and go "yep, that's fine", which I'm sure that it is. I know that Coyote Cookbook recommends getting LTFT within a lower %, but it does take time and datalogs to be that nitpicky.

When I was working on the non WOT part of my tune, I was happy with 5%, but just logged more to get it closer.

 

[Nuked]

Those LTFT's aren't bad at all, especially for an email tune. I can't remember off the top of my head but I believe the Tri-Core is able to adjust around 20-25% on trims without being an issue. Obviously if you start to see them get in the double digits I would look into what up, but where you are at now is not too bad at all. You have to remember too that there are other factors that will change it. Most all 93 is "up to 10% ethanol". You get a tank that is only 7-8% and it will affect your trims. Vacuum leaks, lazy o2 or maf sensor, and temperature can affect it as well. Main thing is to keep an eye on it and if it starts trending in one direction you may want to look into an issue.

 

[ManBearPig]

I swapped to a JLT intake and am agin looking at fuel trims very closely. I have had one revision from Lund but the trims are still off farther than I’d like to see. Idle long term trims have learned around -5% and WOT is always -6%. Light throttle cruising and regular driving is however very tight and never strays from 2%.

Lund says this is close enough but my OCD wants it closer. Thoughts?

 

[ManBearPig]

Edit, here’s a log I loaded up in case anyone would like to review it. I would very much appreciate input

https://datazap.me/u/manbearpig/16gt-lth-jlt?log=0&data=1

 

[Zelek]

Just do datalogs and tell them you want your fuel trims as tight as possible. That's all you can really do. It will require a few back and forth.

 

[BigBlue]

Edit, here’s a log I loaded up in case anyone would like to review it. I would very much appreciate input

https://datazap.me/u/manbearpig/16gt-lth-jlt?log=0&data=1

Had a look at your logs. Here's what I saw:

• Net fuel trims at WOT are within 4-7% which is fine (combined STFT and LTFT). AFR's are in the 11.9's-12.0's which is fine on E85 which I can see you are running.
• Overall at WOT, timing builds slowly towards a peak of 31.3, knock is stepwise more negative as RPMs increasing noting timing is being added to meet the targeted total and the saftot (total timing after all corrections) increases smoothly.
• The only knock really I see is a bit of tip in knock when you go heavy on the throttle suddenly. It resolves quickly and timing is added pretty smoothly up to peak and only drops in between shifts, then grows again. This is healthy.

No concerns really that I see sir. If you "perfect" the LTFTs now, they will just change when the weather gets hotter, or colder. Dont chase an endless race, just make sure they are within 10%, AFRs are healthy and knock is in control and you are golden sir.

Below is a graph showing where any knock (positive numbers for knock counts, nothing more than 1-2 degrees tip in really showing) are occurring, all right at the tip in of throttle and quickly decreasing to negative values (adding timing).

 

[ManBearPig]

Had a look at your logs. Here's what I saw:

• Net fuel trims at WOT are within 4-7% which is fine (combined STFT and LTFT). AFR's are in the 11.9's-12.0's which is fine on E85 which I can see you are running.
• Overall at WOT, timing builds slowly towards a peak of 31.3, knock is stepwise more negative as RPMs increasing noting timing is being added to meet the targeted total and the saftot (total timing after all corrections) increases smoothly.
• The only knock really I see is a bit of tip in knock when you go heavy on the throttle suddenly. It resolves quickly and timing is added pretty smoothly up to peak and only drops in between shifts, then grows again. This is healthy.

No concerns really that I see sir. If you "perfect" the LTFTs now, they will just change when the weather gets hotter, or colder. Dont chase an endless race, just make sure they are within 10%, AFRs are healthy and knock is in control and you are golden sir.

Below is a graph showing where any knock (positive numbers for knock counts, nothing more than 1-2 degrees tip in really showing) are occurring, all right at the tip in of throttle and quickly decreasing to negative values (adding timing).

Thanks very much for the review. What makes it look like this is on e85? I’m on 93. I know I see a lot of spark on 93 but assumed that’s just because my pump gas is quite good.

I don’t usualy look at AFR, but monitor lambda, which hovers around 1.0 except for WOT which is .83-.85, which is what is shown on this log. Where are you seeing the AFR’s of 11.9-12.0 at, I can’t even find that parameter here.

 

[BigBlue]

Thanks very much for the review. What makes it look like this is on e85? I’m on 93. I know I see a lot of spark on 93 but assumed that’s just because my pump gas is quite good.

I don’t usualy look at AFR, but monitor lambda, which hovers around 1.0 except for WOT which is .83-.85.

Lambda is commanded targets while the AFRs are measured from the O2's. If your AFRs are good and trims combined are less than 10% per bank, you should be fine. Ignore the E85 comment, had a brain fart lol. The AFR multiplied by the stoich of the fuel you are using shows your actual AFR. That doesnt tell me what fuel you're using, my brain is jammed today.

0.85 x 14.1 (pump 93) = 11.985, very safe.

 

[ManBearPig]

Lambda is commanded targets while the AFRs are measured from the O2's. If your AFRs are good and trims combined are less than 10% per bank, you should be fine. Ignore the E85 comment, had a brain fart lol. The AFR multiplied by the stoich of the fuel you are using shows your actual AFR. That doesnt tell me what fuel you're using, my brain is jammed today.

0.85 x 14.1 (pump 93) = 11.985, very safe.

Thanks again. I keep getting hung up on the trims. I guess I hoped to see them within 2-3%, not 5-6%.

Is rescaling the maf as simple as taking 2% fuel out? Maybe there is more to revising the tune to get the trims tighter than I realize.

 

[BigBlue]

Thanks again. I keep getting hung up on the trims. I guess I hoped to see them within 2-3%, not 5-6%.

Is rescaling the maf as simple as taking 2% fuel out? Maybe there is more to revising the tune to get the trims tighter than I realize.

No prob. Just ignore the trims if they are less than 10%. The OEM tune and codes dont show until you hit 15-20% off anywho. It all varies with temperature, altitude/pressure, humidity, etc. Your logs look good, have fun with it!

 

[Nuked]

Listen to BigBlue

 

[ManBearPig]

Are long term trims within 5-6% close enough to successfully run a flex fuel tune? I believe the pcm learns ethanol content based on the error it sees in the trims and having them tight is even more important on a flex time than straight 93 or straight E.

On that note I don’t know how much gain I’d see from flex anyway since I already see 30* on 93.

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