STFT spike to +25% briefly at low throttle input?

[TriPinTaZ]

So I have been chasing this little gremlin and cannot find a reason why it does this. But when I am at low speeds and just start to get on the throttle, sometimes my LTFT's will both jump to 25% + and Torque Management Advance will pull some timing. Then as soon as the STFT's return to normal the TMA drops to zero. This is not affecting Long Term Fuel Trims at all. I suspect this could be a Catalyst Test??? Any one have any ideas?

I have AFE mids and the rear O2 efficiency test is disabled so that I do not get any codes. The master Catalyst Test is still enabled though. I may disable this and see if it goes away but was wondering if anyone had some other insight.

15.hpl


STFT.PNG


Thanks

[jpierro79]

no one is going to be able to help unless you state what car your tuning what mods are done to it what motori is in it and without an actual datalog posted not just a picture/

[TriPinTaZ]

Eh I was hoping another advanced tuner may have had the same issue and if anyone had specifics on the Catalyst Test in the Gen V's.


Anyhow, car is a 2015 C7 Z51 M7. Ported Intake Manifold, AFE Intake, ARH Midlength Headers. Datalog attached.


15.hpl

[Jeff7577]

You aren't graphing the O2 voltages but you can see they are pretty much pegged lean which will drive stft up quickly. I just looked at the log. You can see that your injectors shut off (0 ms) at what appears to be part throttle, which causes both o2 sensor to go lean and then it commands 25 to force it rich again. I can look at it more later.

Edit - looked again...its not part throttle.

[pjs]

Mine does the same thing; 2016 C7 Z51 M7 with Magnuson...Always wondered about it...

[TriPinTaZ]

You aren't graphing the O2 voltages but you can see they are pretty much pegged lean which will drive stft up quickly. I just looked at the log. You can see that your injectors shut off (0 ms) at what appears to be part throttle, which causes both o2 sensor to go lean and then it commands 25 to force it rich again. I can look at it more later.

Edit - looked again...its not part throttle.

I do see the O2's are asking for more fuel but it's very odd. The car isn't lean there and it doesn't seem to affect the LTFT's. And what is even more curious to me is why is Torque Management Advance kicking in for the duration and then drops to 0 as soon as the O2s go back to normal operation?

Mine does the same thing; 2016 C7 Z51 M7 with Magnuson...Always wondered about it...

Sometimes it makes part throttle feel sluggish, but other than that it doesn't have any adverse affects. I just wish I knew why it did it. I've wondered if it could be VE correction or Catalyst Test or maybe MAF/MAP(VE) blend factor at low RPM and Airflow values.

[Higgs Boson]

put it in open loop and see if there is a change in lambda.

seems like a test to me though.

[5FDP]

I can make my 2016 Silverado do that like clock work when idling in park. If you hit the throttle to over say 2,000-2,500 and just let off it will peg the STFT at 25% as it comes back down to 1000-1,300rpm. The idle will hang for a second and then drop right to 550-600rpm. I noticed it do the same thing as I coasted down at random speeds too.

I'm very new to the GEN 5 computers and vehicles but I noticed that right away with one or two logs.

[jpierro79]

every engine characteristics are different cant expect your problems to be solved by data logs without the original tune to see if something youve changed effects the datalogs. Your not guarding any secrets wit your mods and youve ported a plastic intake manifold.??If you have ported any intake manifold youve changed the volume hence destroying any calculations so if you havent changed your intake volume to match you will destroy your calculations. Just cause you post a problem without any info and someone doesnt ask for info it actually mean they have less experience as there are certain expected values with each vehicle. Any probems you may have may be due to your "porting" I cant begin to explain flow dynamics and the mathematical calculations so if you dont post what youve done to the tune no one can truly fix your problems. If you truly wish you solve your problems you have to share all information. It just doesnt work that way. I may not be listed as a senior tuner here but its only dictated on posts count not the actual technilogical information of that individual. Ive tuned Vw gti, wrx sti, camoro, other gm vehicles and with different operating systems. Like cobb efi live hptuners, sct and ive been repairing for 20 years and tuning for 10 years. So post count does not dictate knowledge level. It took me 2 weeks to learn entire hptuners concept of tuning as crossing from cobb efi live and sct it was not complicated. With that being said if you want my help we need your original tuned pulled from car and changes to see if we can help you. Ive posted my tune even though it is as safe as the best and more. I wont get into details but lets just state this. I went to one of the biggest names on the east coast cause i didnt use hptuner before. Then after drive ability problems then went to a "renoun" local tuner being a 3 hour drive only to end up with a tune with 13.5 at 10 psi at 2600 rpm which is unsafe and to top it off a stumble at 2500. So if you want my help I can but i need to see what youve changed to guide you to possible fixes. There is no one out there with perfectred gen V tunes as if you can perfect them in only 3 years your a god. Look im not trying to say im better than everyone else as we all must learn as we go but hiding info only is a detriment to your fixing your own problems.

[TriPinTaZ]

every engine characteristics are different cant expect your problems to be solved by data logs without the original tune to see if something youve changed effects the datalogs. Your not guarding any secrets wit your mods and youve ported a plastic intake manifold.??If you have ported any intake manifold youve changed the volume hence destroying any calculations so if you havent changed your intake volume to match you will destroy your calculations. Just cause you post a problem without any info and someone doesnt ask for info it actually mean they have less experience as there are certain expected values with each vehicle. Any probems you may have may be due to your "porting" I cant begin to explain flow dynamics and the mathematical calculations so if you dont post what youve done to the tune no one can truly fix your problems. If you truly wish you solve your problems you have to share all information. It just doesnt work that way. I may not be listed as a senior tuner here but its only dictated on posts count not the actual technilogical information of that individual. Ive tuned Vw gti, wrx sti, camoro, other gm vehicles and with different operating systems. Like cobb efi live hptuners, sct and ive been repairing for 20 years and tuning for 10 years. So post count does not dictate knowledge level. It took me 2 weeks to learn entire hptuners concept of tuning as crossing from cobb efi live and sct it was not complicated. With that being said if you want my help we need your original tuned pulled from car and changes to see if we can help you. Ive posted my tune even though it is as safe as the best and more. I wont get into details but lets just state this. I went to one of the biggest names on the east coast cause i didnt use hptuner before. Then after drive ability problems then went to a "renoun" local tuner being a 3 hour drive only to end up with a tune with 13.5 at 10 psi at 2600 rpm which is unsafe and to top it off a stumble at 2500. So if you want my help I can but i need to see what youve changed to guide you to possible fixes. There is no one out there with perfectred gen V tunes as if you can perfect them in only 3 years your a god. Look im not trying to say im better than everyone else as we all must learn as we go but hiding info only is a detriment to your fixing your own problems.

I'm not sure who you are preaching to here but you certainly have me mistaken. I'm not hiding anything. Any pro tuner that makes a living tuning cars is not going to be threatened by my tuning. Also, I've been doing this since LT1 edit days back in the late 90's. I've tuned quite a few Subaru's with Cobb's stuff as well. I have a very high understanding of GM's Gen 3, 4 and 5 stuff. My career requires that I have the ability to grasp things like this. So while I get you thought you might be posting to some newb that doesn't know what a MAF table is, I can assure you I am very advanced in this world.

I didn't see how posting my tune would really help at all but here it is. Current Tune vs Bone Stock. Higgs is the only one that offered some direction in thinking about a solution. I'm not asking for a solution here but rather ideas and directions to investigate. Hence why I didn't post up all my stuff and wait for a good Samaritan to come along and solve my problems. If you want a crack at it, go ahead, take a look. Ported manifold doesn't actually change the volume enough to really need to change the manifold volume in my opinion. It's not like you are gaining any real actual volume, you're just improving airflow.

Mods: Ported IM, Ported TB, AFE CAI, ARH Midlength catted headers, Borla catless X, Borla S-Type NPP

Nothing special on this one. Car runs real hard. Flabbergast me oh wizard

Taz.014-CurrentTune-Good.hpt
Stock_2015_Corvette_Z51.hpt

[Camaro6]

DFCO should cut the fuel when you let off, so set it at 1,050rpm instead of 1,300 which will correct it to a certain extent depending on driving habits. Alot of times you're cruising at a low rpm, maybe under 1,300rpm, or keep your foot on the gas a little, get under the 1,300 and no fuel cut.

If you need more, log inj pulse width, injector tip temp, intake valve temp, rpm, map, zero pedal tq, coolant temp, and fuel rail pressure (hpfp - mpa) Send me the log with these items logged if the first option doesn't correct it.

[littlefield]

One thing that?s been hard for my performance perception to get calibrated on is the difference between pedal position and throttle position. Because of the Driver Demand function the 2 may not match at all and, of course, it?s the throttle position your motor cares about. As I mess with the DD table I?ll see small changes in pedal result in large changes in throttle. So you have to keep this in mind and really look at throttle position to understand your engine performance. Understand torque management to then understand how that will feel and affect the drivetrain.
I?ve got a Whipple and I believe I?m seeing the effect of the bypass valve closing. I need to log and look for sharp changes around the area the valve closes, -5inHg MAP on mine. Don?t know how to tune around that but I can give it the old Aggie try.

[TriPinTaZ]

DFCO should cut the fuel when you let off, so set it at 1,050rpm instead of 1,300 which will correct it to a certain extent depending on driving habits. Alot of times you're cruising at a low rpm, maybe under 1,300rpm, or keep your foot on the gas a little, get under the 1,300 and no fuel cut.

If you need more, log inj pulse width, injector tip temp, intake valve temp, rpm, map, zero pedal tq, coolant temp, and fuel rail pressure (hpfp - mpa) Send me the log with these items logged if the first option doesn't correct it.

My issue is not happening in the operating parameters of DFCO. I am accelerating from a stop light so DFCO is not involved.

One thing that?s been hard for my performance perception to get calibrated on is the difference between pedal position and throttle position. Because of the Driver Demand function the 2 may not match at all and, of course, it?s the throttle position your motor cares about. As I mess with the DD table I?ll see small changes in pedal result in large changes in throttle. So you have to keep this in mind and really look at throttle position to understand your engine performance. Understand torque management to then understand how that will feel and affect the drivetrain.
I?ve got a Whipple and I believe I?m seeing the effect of the bypass valve closing. I need to log and look for sharp changes around the area the valve closes, -5inHg MAP on mine. Don?t know how to tune around that but I can give it the old Aggie try.

Not sure if you're trying to offer assistance? It is not a DD issue. Driver Demand is not that difficult once you understand the torque model and what to log and how to make sure your Driver Demand is commanding enough based on the changes you make in the torque coefficients. All my DD and Coefficents are good. My issue is somewhere else.

I disabled the master Catalyst Test and will report back once I get some time to datalog and try to replicate the conditions. If that doesn't work I will try Higgs recommendation to force open loop. Also, I'm thinking about increasing the manifold volume just to make the dynamic airflow coefficients final calculation a higher value and see if it affects the problem. But this can also cause other problems.

[DSP RACING]

trippin taz

this does actually does change the volume of the air charge. I have been building engines for a very long time and with the mods mentioned above it changes the VE which in turn requires different fueling requirements. If it where me I would go back and review the file that you started with and maybe calculate the airflow improvement and apply that to the fueling table and see what it does. just a idea. best of luck bro please keep us updated.

[Ghostnotes]

every engine characteristics are different cant expect your problems to be solved by data logs without the original tune to see if something youve changed effects the datalogs. Your not guarding any secrets wit your mods and youve ported a plastic intake manifold.??If you have ported any intake manifold youve changed the volume hence destroying any calculations so if you havent changed your intake volume to match you will destroy your calculations. Just cause you post a problem without any info and someone doesnt ask for info it actually mean they have less experience as there are certain expected values with each vehicle. Any probems you may have may be due to your "porting" I cant begin to explain flow dynamics and the mathematical calculations so if you dont post what youve done to the tune no one can truly fix your problems. If you truly wish you solve your problems you have to share all information. It just doesnt work that way. I may not be listed as a senior tuner here but its only dictated on posts count not the actual technilogical information of that individual. Ive tuned Vw gti, wrx sti, camoro, other gm vehicles and with different operating systems. Like cobb efi live hptuners, sct and ive been repairing for 20 years and tuning for 10 years. So post count does not dictate knowledge level. It took me 2 weeks to learn entire hptuners concept of tuning as crossing from cobb efi live and sct it was not complicated. With that being said if you want my help we need your original tuned pulled from car and changes to see if we can help you. Ive posted my tune even though it is as safe as the best and more. I wont get into details but lets just state this. I went to one of the biggest names on the east coast cause i didnt use hptuner before. Then after drive ability problems then went to a "renoun" local tuner being a 3 hour drive only to end up with a tune with 13.5 at 10 psi at 2600 rpm which is unsafe and to top it off a stumble at 2500. So if you want my help I can but i need to see what youve changed to guide you to possible fixes. There is no one out there with perfectred gen V tunes as if you can perfect them in only 3 years your a god. Look im not trying to say im better than everyone else as we all must learn as we go but hiding info only is a detriment to your fixing your own problems.

I'm really impressed..

[5FDP]

More paragraphs.

[jpierro79]

why do people troll instead of helping claiming garbage like OHH its nothing special. If you here help if not go get a life and do something else please. if your going to bash someone grow up either help or find something else to do as that is the point of the forum to help each other. Please take your ego elsewhere as your doing nothing but damaging the hptuner name and its forums by bashing other people.

[Camaro6]

My issue is not happening in the operating parameters of DFCO. I am accelerating from a stop light so DFCO is not involved.



Not sure if you're trying to offer assistance? It is not a DD issue. Driver Demand is not that difficult once you understand the torque model and what to log and how to make sure your Driver Demand is commanding enough based on the changes you make in the torque coefficients. All my DD and Coefficents are good. My issue is somewhere else.

I disabled the master Catalyst Test and will report back once I get some time to datalog and try to replicate the conditions. If that doesn't work I will try Higgs recommendation to force open loop. Also, I'm thinking about increasing the manifold volume just to make the dynamic airflow coefficients final calculation a higher value and see if it affects the problem. But this can also cause other problems.

Sorry, I thought it was when coming off the gas. Noticed that was another person who posted. I had the same issue with my LT4 S/C on the LT1 and VE didn't fix it all the way without it being really jagged. I smoothed the VE out and then went into the fueling table for adjustments as DSP RACING mentioned. I bumped up the fueling in the areas I was lean based on intake valve temp and fuel pressure. I used the temperature adder section, which can also be used to lower fuel if needed.

[TriPinTaZ]

You aren't graphing the O2 voltages but you can see they are pretty much pegged lean which will drive stft up quickly. I just looked at the log. You can see that your injectors shut off (0 ms) at what appears to be part throttle, which causes both o2 sensor to go lean and then it commands 25 to force it rich again. I can look at it more later.

Edit - looked again...its not part throttle.

DFCO should cut the fuel when you let off, so set it at 1,050rpm instead of 1,300 which will correct it to a certain extent depending on driving habits. Alot of times you're cruising at a low rpm, maybe under 1,300rpm, or keep your foot on the gas a little, get under the 1,300 and no fuel cut.

If you need more, log inj pulse width, injector tip temp, intake valve temp, rpm, map, zero pedal tq, coolant temp, and fuel rail pressure (hpfp - mpa) Send me the log with these items logged if the first option doesn't correct it.

Camaro6, you might be on to something. As I was looking today at my logs after changing some things, of which none made a difference, I noticed that this always happens AFTER a DFCO event. So I let off the throttle, car goes into DFCO as it should, O2's go way low on milivolts signaling a lean condition as it should since the Injectors are off. Then as soon as I hit the throttle the car comes out of DFCO, injectors are back on, but STFT's are +25% on both banks for a short period of time. Then once the O2's snap back to oscillating, the STFT's return to normal and the Torque Management Advance drops back to zero.

In my latest tune I tried turning off all Cat Tests and increasing manifold volume size. Neither did anything. I may try forcing open loop as Higgs suggested but I don't have my wideband in the car since it was already tuned.

[TriPinTaZ]

Here is the log from the latest tune as mentioned above. Every time I exit DFCO the STFT's peg to 25%+ and TMA pulls timing for a short period of time.

15.2.STFT.25.DFCOEXIT.hpl