Combustion Stability Limit

[SlowSTExploder]

Hello everyone,

As the title states, i want more info on why this limit comes up even though you have these limits Cal'ed out..
I've been fighting this limit with my 3.0t Explorer ST, I've searched the forum, looked at multiple posts, patents, etc.

ive tried all the fixes suggested whether it was removing the limiter completely, to adjusting the torque tables. no matter what i do this limiter likes to pop up during an entire pull.
i would like some extra input, other things to try, maybe im missing something in my own tune that im not seeing, maybe this could be something mechanical?

mostly everything all the important parameters that need to match up or atleast follow eachother closely (desried vs actual).
desired load is higher than airload, which still kicks on the popcorn limits which i thought, if airload is lower than desired, popcorn shouldnt be popping up..
anyway any help is welcome and i know some of you gurus know some work around, i understand that time is valuable as well as knowledge, and comes with a price. feel free to DM me if you feel like this info something isnt something that you want to openly discuss here.

thanks



Screenshot 2025-02-18 105937.png

modified18_pumpgasV3TEST_OSmyst22.hpt

orignialOSmyst22.hpt

88988.hpl

[bmpcamry09]

Don't take this the wrong way, just trying to help, but your file needs a lot of work.

Theres nothing really wrong with hitting that limiter, it's one of the most critical in keeping the rods in the block. It goes hand and hand with popcorn.

Did someone start this tune for you and then you did some copying over? Because your scalars are all screwed up throughout the tune, especially under spark, all your scalars changed but you didn't make any actual timing changes worth anything, so your PCM isn't going to read those tables correctly.

Are you logging mapped points? Doesn't look like you are, but you managed to make speed density changes anyways? Some of those speed density changes look off.

A few other big things I noticed:

-Your pulling timing, if that's 93 octane, it's crappy 93 octane.
-Only timing changes are around cylinder pressure limits, but all your timing scalars have been changed with no changes in your actual tables, hurting your power.
-Some SD stuff was tweaked but you haven't touched any maximum load stuff under airflow>speed density>maximum load.
-What's up with your torque tables? You increased load scalar but reduced indicated torque. There is a large discrepancy in your log between demanded torque and actual because of this. The torque tables are all off and need completely redone.
-Your driver demand table has no changes at 90-100 percent throttle. You stopped at 79.2.....so at WOT your commanding stock torque.....

[bmpcamry09]

I looked over your file more, I think you need to start from scratch. Disclaimer, I tune pretty much exclusviely 3.5 and 2.7 trucks, but I built a "starter" pump gas tune for you that should be conservative but a better starting point for you. Changes are based on basic Ecoboost tuning principles taught by most of the available tuning courses out there. Obviously use discretion but most of what I did to your file I have great success with on the other platforms. Also gave you a basic trans tune. Let me know how it feels and post up a datalog after. Not many people will get you more than this for no cost.

I did not touch speed density other than Maximum load tables, so keep an eye on fuel trims and adjust as needed.

Something to remember when tuning Ecoboosts is Ford really knows what they are doing when it comes to some of the safety items in the background. For some reason ST guys like to just max stuff out and risk it. That's not how I tune, so that's not how my starter file is set up. You can tune these to feel great while maintaining the integrity of how Ford expects them to operate. No need to remove a bunch of limiters.

Speaking of datalog, I'll see if I can't upload a datalog config for you to add those missing channels in.

ST 3.0 Starter Pump Gas.hpt

Ecoboost.Channels.xml

[SlowSTExploder]

Don't take this the wrong way, just trying to help, but your file needs a lot of work.

Theres nothing really wrong with hitting that limiter, it's one of the most critical in keeping the rods in the block. It goes hand and hand with popcorn.

Did someone start this tune for you and then you did some copying over? Because your scalars are all screwed up throughout the tune, especially under spark, all your scalars changed but you didn't make any actual timing changes worth anything, so your PCM isn't going to read those tables correctly.

Are you logging mapped points? Doesn't look like you are, but you managed to make speed density changes anyways? Some of those speed density changes look off.

A few other big things I noticed:

-Your pulling timing, if that's 93 octane, it's crappy 93 octane.
-Only timing changes are around cylinder pressure limits, but all your timing scalars have been changed with no changes in your actual tables, hurting your power.
-Some SD stuff was tweaked but you haven't touched any maximum load stuff under airflow>speed density>maximum load.
-What's up with your torque tables? You increased load scalar but reduced indicated torque. There is a large discrepancy in your log between demanded torque and actual because of this. The torque tables are all off and need completely redone.
-Your driver demand table has no changes at 90-100 percent throttle. You stopped at 79.2.....so at WOT your commanding stock torque.....

Thanks for the honesty, I'm still learning. By no means am I an expert here. So the map that I put up was where I ended up prior to posting this.

I semi understand what popcorn is and it's function, this was more so to understand why or where it's coming up with that limiter, since I'm not remotely close to my desired load unless it just means it's using the lspi tables to reference the max load I want. If that's the case than its a misleading term IMHO.

No I started this by myself from my stock read, the changes that were made were based in what I've read, used examples from others with similar vehicles. The scalars is something I was experimenting with, seeing if changes made affected load, boost etc. Mainly just tinkering seeing what does what.

Yes I've logged load points which is why you see changes to the SD model in those areas my fuel trims were trying to add 15 to 20% fuel, so I adjusted those values to keep the fuel trims closer to +/- 5%, on the upper rpms it was pulling 12% fuel so I adjusted that as well. I tried using the VE Calculator provided by hp tuners, but that would net me larger corrections even when I would use the special paste function adding half the percentage of correction I would get from the logger..

-I live in a high elevation state so I only get 91 as the highest from the pump.

-I was under the impression that the maximum load was only to be changed if you exceed the load in which is preset on those tables, am I wrong on that?

-well here's the thing, before I touched those everything was doing great, than combustion stability limit shows up and I was never able to get back up to 497 engine brake torque, it kept getting limited to 400 or 420 it, which lead me to play with those torque tables to see if it that combustion stability was popping up from the large difference between, indicated, engine brake, desired and ETC torque..

-that was me testing to see if reducing the torque in that area would get the Tq Red<driver demand to change.

Thanks for the pointers , and go through the process one more time.

[Rob@HPTuners]

The LSPI tables are indeed a "clip" on the load.

The thing to keep in mind is that all of this logic and logging parameters flow semi-linearly throughout the code execution. So in simple terms, if step one is determining "desired load" and step two is to clip it to the LSPI tables, the parameters from previous steps don't get back-propagated with the new clipped values. This is actually a good thing because it makes it very easy to pinpoint the source of the issue, once you get the hang of it.

Speed Density and the calculator in particular don't respond well to sweeping changes like that. If you're dealing with the linear part of the curve, you're typically trying to bend some combination of the slope value and the aircharge multiplier value depending on if you are trying to add or remove VE. Can go more into detail on that if you'd like.

[bmpcamry09]

Got your PM slowStExplorer and replied. But figured I'd post public here too.

Something else to keep in mind is since your at elevation, your fuel trims are going to be off a little more than someone not at elevation anyways. That's what long term fuel trims are for. Your PCM will throw a CEL if it's not happy with your fuel trims so long as you don't have that disabled. Also, your speed density scalars in VCM editor will change if you raise the MAP ceiling. It's easy to forget to make the same scalar change in VCM Scanner so that your data is accurate when you copy and paste by half a percent.

Although I have taken most of the available Ecoboost and Ford courses, I am NOT a professional full time tuner, so take what I say with a grain of salt. I have written several tunes for several of my personal vehicles and also many on the side. In my experience there is rarely need to tune on Speed Density on Ecoboost unless your making some big time modifcations like bigger turbos, etc., and even then, speed density is pretty accurate. Some changes to some of the tables, IE maximum load in the speed density tab on ecoboost trucks are common though. It's hard to be accurate with speed density as your basically never going to be 100 percent in one set mapped point except for at idle. If you really want to tune them accurately, you can force the tune to run in one mapped point at a time and road test. But it’s very tedious.

Regarding the scalars, on pump gas, the factory scalars work pretty well. The only ones I sometimes have to touch are cylinder pressure limit and a few fuel pressure related ones. I also occasionally change scalars on transmission tuning as I have general templates for each trans I tune on and some Ford OS files use different scaling for OSS tables.

Don't be hard on yourself. There is a ton of good information on this forum, but a ton of bad information also. If your serious about tuning, it'll take some time and money. Take some courses and try to network with some professionals. Buy tunes from several different companies and ask them to leave the files unscrambled if possible (some will do this for you, some won't). Once you build relationships, some guys will let you see their files and tuning styles and teach you a ton of info that you won't learn on here.

The best advice I ever heard from a very well known Ecoboost tuner who uses the SCT platform is to not try to "reinvent the wheel", meaning don't try to fight Ford's factory logic so much. Dozens of engineers who do this day in and day out develop factory tunes and generally do a decent job to keep 95 percent of drivers happy. It's us nerdy 5 percent that like to tweak stuff. Keep it safe but make it yours.

[SlowSTExploder]

Got your PM slowStExplorer and replied. But figured I'd post public here too.

Something else to keep in mind is since your at elevation, your fuel trims are going to be off a little more than someone not at elevation anyways. That's what long term fuel trims are for. Your PCM will throw a CEL if it's not happy with your fuel trims so long as you don't have that disabled. Also, your speed density scalars in VCM editor will change if you raise the MAP ceiling. It's easy to forget to make the same scalar change in VCM Scanner so that your data is accurate when you copy and paste by half a percent.

Although I have taken most of the available Ecoboost and Ford courses, I am NOT a professional full time tuner, so take what I say with a grain of salt. I have written several tunes for several of my personal vehicles and also many on the side. In my experience there is rarely need to tune on Speed Density on Ecoboost unless your making some big time modifcations like bigger turbos, etc., and even then, speed density is pretty accurate. Some changes to some of the tables, IE maximum load in the speed density tab on ecoboost trucks are common though. It's hard to be accurate with speed density as your basically never going to be 100 percent in one set mapped point except for at idle. If you really want to tune them accurately, you can force the tune to run in one mapped point at a time and road test. But it?s very tedious.

Regarding the scalars, on pump gas, the factory scalars work pretty well. The only ones I sometimes have to touch are cylinder pressure limit and a few fuel pressure related ones. I also occasionally change scalars on transmission tuning as I have general templates for each trans I tune on and some Ford OS files use different scaling for OSS tables.

Don't be hard on yourself. There is a ton of good information on this forum, but a ton of bad information also. If your serious about tuning, it'll take some time and money. Take some courses and try to network with some professionals. Buy tunes from several different companies and ask them to leave the files unscrambled if possible (some will do this for you, some won't). Once you build relationships, some guys will let you see their files and tuning styles and teach you a ton of info that you won't learn on here.

The best advice I ever heard from a very well known Ecoboost tuner who uses the SCT platform is to not try to "reinvent the wheel", meaning don't try to fight Ford's factory logic so much. Dozens of engineers who do this day in and day out develop factory tunes and generally do a decent job to keep 95 percent of drivers happy. It's us nerdy 5 percent that like to tweak stuff. Keep it safe but make it yours.

thank you, i tried your starter file and it ran great, my 91 here must be shit or i got bad gas twice lol but here are some logs on that sorry the are long..

30min drive.hpl
30min drive2.hpl
pull1.hpl
pull2.hpl

[SlowSTExploder]

The LSPI tables are indeed a "clip" on the load.

The thing to keep in mind is that all of this logic and logging parameters flow semi-linearly throughout the code execution. So in simple terms, if step one is determining "desired load" and step two is to clip it to the LSPI tables, the parameters from previous steps don't get back-propagated with the new clipped values. This is actually a good thing because it makes it very easy to pinpoint the source of the issue, once you get the hang of it.

Speed Density and the calculator in particular don't respond well to sweeping changes like that. If you're dealing with the linear part of the curve, you're typically trying to bend some combination of the slope value and the aircharge multiplier value depending on if you are trying to add or remove VE. Can go more into detail on that if you'd like.

i figured as such, its weird too that you can input the stock values and itll still make changes to the sd tables.

id like more info for sure, if youd like to share.

[Rob@HPTuners]

It's not that strange. The calculator is approximating the same math that was used to model the original data, but it's reasonable to expect that there might be slight calculation differences between the two.

Your VE model should not generate errors at elevation, Ford models this along with a bunch of other density corrections, so if you're seeing an error, I don't think there's any harm in trying to tune it out. I will agree that SD changes are usually warranted by more serious modifications to the setup.

The speed density stuff is really complicated, so much so that I haven't had very much luck explaining it to anyone. Most people want to make adjustments at WOT, and 99.9% of the time this is happening at the point that the SD has switched over to a linear representation aka the slope value. So kinda simple, if you want to add fuel, lower the slope value, if you want to remove fuel, raise it. Keep in mind that this adjustment is going to apply linearly to the entire map at that given RPM range, and it will also propagate into the curve portion of the map, which is typically at lower loads. To put that more simply, a WOT adjustment at 4500RPM will also have an effect on low load cruising at 4500RPM for that mapped point. Not everyone hits high RPM and low load points in their driving habits, so this may be a non-issue.

At some point you may realize that lowering the slope value (adding fuel) isn't doing anything anymore. This is because it's hitting the clip that we get from engine displacement and the aircharge multiplier value. To get past this, you'll need to also raise the aircharge multiplier. I would do this carefully because you're essentially telling the tune that it's defying physics. If you still have a 20+% fuel trim, it's probably a mechanical issue.

[bmpcamry09]

I looked over your logs from my starter file. Looks decent for 91 octane. Your turbos are working pretty hard though, inferred speed is way up there, but I am more used to gen 2 3.5 tuning so maybe thats the norm on these, no idea. Probably won't be able to squeeze to much more out at this point. But your fuel trims look good especially for being at elevation. KOM is decent at .5-.6 so your safe and your ST likes the tune.

Since your already on the HP Tuners platform, hit up Adam at ZFG for a tune. Then datalog and compare.

[SlowSTExploder]

I looked over your logs from my starter file. Looks decent for 91 octane. Your turbos are working pretty hard though, inferred speed is way up there, but I am more used to gen 2 3.5 tuning so maybe thats the norm on these, no idea. Probably won't be able to squeeze to much more out at this point. But your fuel trims look good especially for being at elevation. KOM is decent at .5-.6 so your safe and your ST likes the tune.

Since your already on the HP Tuners platform, hit up Adam at ZFG for a tune. Then datalog and compare.

Thank you for double checking! I tried to dm ya but It wouldn't go through.

Anyway it's solid, the offer i still open that I sent to you via DM. You definitely helped me out more than you know.


Yeah the inferred speed has always been high anything passed 17psi is where i would NIP it off at higher rpms, I'm gonna try putting it on e30 and see if it cleans up the low load knock if it doesn't than I might have flex pipe issues causing some vibrations or pinging that the knock sensor may be picking up...

[SlowSTExploder]

Thanks for the information Rob, so is turbo airflow desired, a function of SD calculations, I've never been able to line my actual Lb/m to desired Lbs/m..

[bmpcamry09]

V2 coming your way soon

[SlowSTExploder]

[bmpcamry09]

Try this V2 out.

V2.hpt