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Thread: 2.0 LTG cutting throttle aggressively at half throttle

  1. #1

    2.0 LTG cutting throttle aggressively at half throttle

    Me and my buddy have been working on his 2019 Malibu and the car was running well only problem was that I couldn't get the manifold pressure up. Boost was reading around 20 psi but manifold pressure was only up to 8 psi. Car was running strong. Now we installed a catless downpipe and I deleted the codes for the cat and turns catalyst test off. The car runs great in wot but going from cruising to half throttle will aggressively cut fuel and close the throttle really quick. I could not find what table is causing this. I have tuned many LNF cars and I understand how the tables work in relation to each other. This one has me stumped on what is causing the issue.

    I lowered the wastegates duty cycle, maxed out over boost and underboost tables, lowered timing to avoid knock and also increased knock airmass tables a bit from -2 to 0 and no change. WOT runs great but half throttle does not. It does not knock when this happens but actual boost goes over desired boost by 2 or 3 psi. Any suggestions on what might be happening? I can send a log to anyone that wants to look over it. Thanks

  2. #2
    Post log and tune.

    LTG is GM software, LNF is Bosch software. Outside of the fact they both share the idea of ?torque control? literally not a single line of code is the same.

    If your engine is relatively stock, with stock turbo, there?s no reason to change the wastegate duty cycle.

  3. #3
    I used a bit of what i learned from the LNF on this and i believe that is my mistake. i did bring up the wastegate DC like i had done on my Solstice. here is a log of the issue. it only happened once on this log and i will also post the tune file that was used. i will bring the wastegate values back to stock and retest as i feel that is what is causing the throttle to close quickly.

    throttle cut.hpl
    stockj3 catless.hpt

  4. #4
    i'm pretty sure there's a variable that you can record that's wastegate dutycycle, i'd record that as well in future logs.
    Also if your car is 2016 or newer (E80 controller) that means you have a factory wideband O2 sensor, not sure which variable to record, or if you already record it, but find that signal and record it.

    If the throttle closing problem you are describing at t=11:23:06, then yes, that's because you messed with the wastegate duty cycle too much. if you have a stock turbo, on a relatively stock engine, only minor changes might be needed to that table, but maybe no changes. you put in 100% dutycycle in the 2.6 pressure ratio columns, which means it will try it's hardest to close the wastegate (maximum effort as deadpull would say), when the ECM sees all the cylinder airmass (you're reading 1.53 g/cyl) WAY above what you wanted, the ECM tries to gain control (and protect) the engine by closing the throttle.

    Here's my understanding of how this system works: accel pedal is converted to desired torque. The torque model converts desired torque into desired cylinder airmass. the boost controller converts desired cylinder airmass into desired pressure ratio. the wastegate base dutycycle table + a boost PID controller converts desired pressure ratio into wastegate dutycycle.

    Since you messed with the wastegate dutycycle, all the controls lose their mind because the engine isn't doing what they thought it would, and all the closed loop controllers scramble to gain control of the system however they can, in your case, closing the throttle.

    From the sequence of events i described above, you can see that if you want to get more torque, you need to ask for more torque, and allow a higher pressure ratio, not to mess with the conversion table that turns pressure ratio into wastegate dutycycle.

    There's something odd in your data, the MAP signal seems messed up, I didn't spend any time trying to figure out why it's wrong, but something is odd. when the throttle is open TIAP and MAP should match, only about 1 to 2 kPa different.

    EDIT: you're also knocking here and there, 2 to 3 deg knock retard, not sure if that's real knock, not sure it's acceptable, but it does it at high engine load (high boost, high cylinder airmass) so i'm not sure i'd be comfortable with that. this is a really long, complicated discussion, many opinions, few facts. Don't know if it's real knock or the sensors are too sensitive, don't have an answer for you, maybe someone else will comment on the knock.
    Last edited by TurboCobalt; 03-15-2019 at 04:00 PM.

  5. #5
    Thanks I was sure it was because my actual boost was exceeding desired boost and you have confirmed that with your explanation. So in order to ask for more torque, that would be the peak torque and the other tables in the torque management section correct?

    The MAP signal is also one of my concerns, it has been like that since I first worked on the car. I thought it was maybe not allowing airflow into the manifold and why it was reading that way. There is a major difference in kpa.

    As for the knock, it looks like real knock but it doesn't seem to go away when I pull timing either. The knock sensor settings have not been changed, if they are anything like the last knock sensors they are pretty sensitive. And I thought I was logging the o2 sensor I'll take a look again thanks.

  6. #6
    Advanced Tuner lt1z350's Avatar
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    to make more boost on the early ones your waste gate table will end up being lower in the upper parts of the table so that you do not over shoot the requested boost which then closes the throttle. the 2017 and 2018s have some other type of control that is missing in hpt. I havent yet figured it out but on a 2013-16 ats or 16 camaro I can request 41.5 psi and then setup my dc boost table to hold a absolutely perfect 21 psi. No overshoot no spikes and throttle stays open. I have been tuning the ltg since 2013 and my ats and am very good with them and I still have to fight and manipulate the 17s and 18s to have over 20 psi and hold the throttle wot. Now a hint is a manual 2017 2017 ats has zero issues with boost control and throttle closing its more like a 2016 so thats telling me the tcm is the limit. The one 2017 automatic I have tuned that didnt fight me that much did have a unlocked tcm and I was able to so far make over 400 whp on a zfr with it. Prior the the turbo swap and tcm unlock it was a bitch to hold 20 psi and be wot. Something in the tcm and still think tables missing on the ecm side that gm added from the 2016 to the 2017 platform. I can hit 27 psi on a 2013-16 of course it will just get hot with out some serious supporting mods but did have a rail setup for 300 feet races that was pretty much making all the boost it could which was 27 psi as was over in around 4.5 seconds for the 300 feet run on sand in a 2200 lbs rail. Fighting a 2018 right now that just will not make more boost and the kicker is I just did another 2018 a few weeks ago and got it to hold 20 psi and wot and that tune in this car is not happy. I have been told by a buddy using efilive and hpt to tune in russia that the ltg is missing a lot of tables he is using to make them work right. I have to pull his tune and get some more id numbers off tables then request hpt to add them to the next beta. I have done it with one so far a torque over speed table that falls in limits under speed limit 1 as saw it was very low on the efilive scan and was also told that helped the boost fall off when hits 90-100 mph that all these late seem to have with them. I am willing to help share some of my early tuning tricks but someone with a 2018 is going to have to work with me so can work this out once and for all. Tired of it taking so many trys just to get it to wot and 20 psi when none respond the same. Also for those logging the max torque pid you will see that on an early by commanding 42 psi it will take max torque way up and out of the way. When delivered torque crosses over max torque thats when the throttle closes. There is no table for this directly its a combination of many inputs where on a 2016 if you were to just raise the pressure delta table then request boost goes up and so does max torque. sorry screen shots writing not great but trying to show you my point on two cars one early one late and you can do the exact same things to the late as early and gets you this outcome.
    Attached Images Attached Images
    First 9 second 6th gen lt4 zl1 stock blower/cam/heads boost only pass. Current record holder Builder/owner/tuner. 9.93@138/10.01@140 back to back passes

    2013 cadillac ats premium 2.0t Big turbo-gone
    2016 cts v-sport tuned and fast.
    2007 tahoe 5.3 lsa blower on 14 lbs boost 6l80e swap
    2017 zl1 a10 5 inch cold air/2 inch headers/ 9.55 lower/ e85/bigger hx /zr1 95mm tb/ methanol injection/ ported blower nose.

  7. #7
    I brought the wastegate numbers down on the higher Delta pressure area, and helped with the throttle cut. I am only running around 20-22 psi and it is hitting Target and not overshooting now. That is all great advice thatnks. I would appreciate some help on tuning these engines, currently I was only working on this Malibu but I plan to do more now that I like how these cars run tuned.

    The next step for this Malibu will be stage 2 cams from zzp. Has anyone tuned for cams on this engine? I have done cams in 2.4 and 2.0 ecotecs. Hopefully that experience will help with the LTG engine

  8. #8
    Advanced Tuner lt1z350's Avatar
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    I have tuned two cars now using zzp cams and their is no power to be found eithcthem over stock. Actually the last one off the dyno made less with the cams then any I have tuned with out cams running similar bolt ons. I didn’t get a chance to play with the actual cam settings on the car it’s still running what zzp had put in it when they tuned it which the car was miserable and slow. So they can’t even tune what they grind correctly or the cams are just that bad for how they are ground. The only benifit I have seen so far is the fuel lobe. But for the grind being larger it’s doing zero for power on the dyno anyway when compared to a similar build with no stock cams. It has moved the power up a little but not made any significant increase. Maybe it’s in the cylinder head or manifold just cannot flow more. The car isn’t local to me so I cannot play isn’t it much. I spent more time making it idle and drive normal again as that was so poor with the zzp tune.
    I got the 2018 to stay open now I had to get super aggressive on the max delta pressure compared to a 16 and down. But now holding 21 psi nice and steady. Over that with a stock ic it just makes too much heat and hurts power. Watch the iat temps 21 psi vrs 22 and can see it climb a lot faster at 22 limiting timing as kr will start to show up pretty heavy if not careful. Last Malibu I did had 21 psi held 6-8 degrees timing no problem with out kr at all on 95ron as it’s over seas.
    First 9 second 6th gen lt4 zl1 stock blower/cam/heads boost only pass. Current record holder Builder/owner/tuner. 9.93@138/10.01@140 back to back passes

    2013 cadillac ats premium 2.0t Big turbo-gone
    2016 cts v-sport tuned and fast.
    2007 tahoe 5.3 lsa blower on 14 lbs boost 6l80e swap
    2017 zl1 a10 5 inch cold air/2 inch headers/ 9.55 lower/ e85/bigger hx /zr1 95mm tb/ methanol injection/ ported blower nose.

  9. #9
    Vasquezz1228, it really depends what you're trying to do. If the goal is a "record setting" LTG, then yes, you'll need cams, ported head, forged internals, huge turbo etc. But it doesn't seem like that's what you're after; to me it seems like you're looking for a relatively mild build, and if that's the case, i dont think cams are for you. Like lt1z350 said, the fuel lobe may help you, but not the cam grinds. There are better ways to spend your money that will gain you more than the cams. define your goal, then we can help you select the hardware that will optimize your build (for the lowest cost). The limiting factor is not the cams, it is the turbo. first decide if your build will keep the stock turbo or get a bigger one. If you keep stock turbo: catless downpipe helps because it reduces back pressure, allows the turbine to be more effective. cold air intake helps, reduces pressure drop to compressor inlet, and make sure its a real cold air intake that ingests COLD air, not engine bay heat. like lt1z350 stated better intercooler, less pressure drop across intercooler, and colder charge air temp. notice most of the hardware changes are there to make the turbo's work easier. then depends if you need fueling mods to keep up with the air.

    personally i'm biased to some sort of ethanol blend, to me it seems LTG is very knock limited, something like a 50/50 E10&E85 mix, what people call "E47", that increases your knock resistance significantly, lot of power to be gained there by advancing spark. but you either have to mix fuel all the time, or add (and tune) a flex fuel sensor, it's still unclear to me if this controller can support a flex fuel, and you need more fuel if you run ethanol so keep an eye on fueling system, this is probably where that bigger fuel lobe on the cam may be needed.

    Disclaimer : i've never tuned an LTG with HPtuners, and i don't own an LTG, so take my input with a grain of salt

  10. #10
    Senior Tuner cobaltssoverbooster's Avatar
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    If the motor is apart then all you need to do is a bowl blend. Cams are pretty good stock so get something close to stock but with the fuel love upgrade. Forged internals to your preference, and a smaller frame turbo. I like the ones that are around gt28-30 size. Zfrs are nice for this.

  11. #11
    Tuner ZeroBoostBuick's Avatar
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    The throttle problem might be torque management.

    Torque Management / General / Max Torque/Peak Torque table

    Driver Demand / Map A. Once you're done tuning map A, then copy it to Map B and C.
    They dictate if you're allowed to have to power you ask for or not allowed, hence the throttle closing to reduce power.

    Maybe you already know this stuff, but I thought I'd point it out anyways.

    I can't tell ya what to change them to,
    but I can tell you in the Driver Demand Map A it's not good to change the numbers in the 12% the 8% the 4% the 2% and the 0% Throttle rows.

  12. #12
    Tuner Boost's Avatar
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    Quote Originally Posted by lt1z350 View Post
    There is no table for this directly its a combination of many inputs where on a 2016 if you were to just raise the pressure delta table then request boost goes up and so does max torque
    Is this "Pressure Delta Factor" in the E80, and does it work similarly in say a '17 1.5? Thank you much!
    - Roland
    GM dealer tech since 2005
    '01 Z28 LS1/T56
    t-tops
    stock 241 heads, stock cam,
    stock muffler, factory wheels

    8.2 @ 86
    (1/8th mile with 255 Toyo Proxes)
    I am learning...

  13. #13
    Advanced Tuner lt1z350's Avatar
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    Quote Originally Posted by Boost View Post
    Is this "Pressure Delta Factor" in the E80, and does it work similarly in say a '17 1.5? Thank you much!
    yes we learned the ltg by some guys that were already messing with the sonic back in 2013 on the smaller motors. There is a good sonic thread that a guy did his car and walks you through the changes he made and then did a log and shows how it affected the car. Its pretty accurate and good for a new tuner on this type system.
    The ltg does support flex from 2013 to 2015 then a hole in the 2016s something to do with no pin in the ecm then 17 and 18s can also support the flex sensor in the tune. I currently tune a bunch of these for guys and f you run around a 7 gph nozzle and 50/50 methanol you can run full e85 on the stock fuel system up into the 380whp range. A 10 gph nozzle will get you over 400whp on e85. there are ways around the stock fuel system that work well and on meth and e50 plus you can get over 14 degrees of timing in these on 21-22 psi and make great power and will fend off knock. I have 18 degrees in one and its very fast on a stock turbo. A zfr build on 26 psi running 14 degrees on a 10 gph nozzle 50/50 mix making over 420whp.
    You have to be very careful as they are so kr sensitive and wont hold up like the older 2.0t engines. I believe its a piston ring issue chamber temps get crazy and the piston ring butts its ends and breaks the ring lands typically on number 3 first. Seen stock cars even do this on a stock tune and why I feel gm got greedy on the top ring gap and didnt run it big enough and add more pressure and more temp and its a recipe for failure of not careful and if dont know these well. Hopefully the smaller 1.8 and 1.5 dont have the same issues. I have tuned one spark and had good results with it so far on tune only setup. If have questions just email or pm me im always around to help answer questions or will do a full tune with logging support and at the same time teach you to tune your own car.
    First 9 second 6th gen lt4 zl1 stock blower/cam/heads boost only pass. Current record holder Builder/owner/tuner. 9.93@138/10.01@140 back to back passes

    2013 cadillac ats premium 2.0t Big turbo-gone
    2016 cts v-sport tuned and fast.
    2007 tahoe 5.3 lsa blower on 14 lbs boost 6l80e swap
    2017 zl1 a10 5 inch cold air/2 inch headers/ 9.55 lower/ e85/bigger hx /zr1 95mm tb/ methanol injection/ ported blower nose.

  14. #14
    Tuner Boost's Avatar
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    Quote Originally Posted by lt1z350 View Post
    yes we learned the ltg by some guys that were already messing with the sonic back in 2013 on the smaller motors. There is a good sonic thread that a guy did his car and walks you through the changes he made and then did a log and shows how it affected the car. Its pretty accurate and good for a new tuner on this type system.
    The ltg does support flex from 2013 to 2015 then a hole in the 2016s something to do with no pin in the ecm then 17 and 18s can also support the flex sensor in the tune. I currently tune a bunch of these for guys and f you run around a 7 gph nozzle and 50/50 methanol you can run full e85 on the stock fuel system up into the 380whp range. A 10 gph nozzle will get you over 400whp on e85. there are ways around the stock fuel system that work well and on meth and e50 plus you can get over 14 degrees of timing in these on 21-22 psi and make great power and will fend off knock. I have 18 degrees in one and its very fast on a stock turbo. A zfr build on 26 psi running 14 degrees on a 10 gph nozzle 50/50 mix making over 420whp.
    You have to be very careful as they are so kr sensitive and wont hold up like the older 2.0t engines. I believe its a piston ring issue chamber temps get crazy and the piston ring butts its ends and breaks the ring lands typically on number 3 first. Seen stock cars even do this on a stock tune and why I feel gm got greedy on the top ring gap and didnt run it big enough and add more pressure and more temp and its a recipe for failure of not careful and if dont know these well. Hopefully the smaller 1.8 and 1.5 dont have the same issues. I have tuned one spark and had good results with it so far on tune only setup. If have questions just email or pm me im always around to help answer questions or will do a full tune with logging support and at the same time teach you to tune your own car.
    That is wonderful information and option. I thank you. Currently just wanting to add an extra 20 hp to a stock 1.5 on pump gas and did not want to chase my tail on boost as I did in my prior 1.4t and LHU. Should be simple enough but as the controller and engine is new I've been stalking this thread and others, looking for hints. Sorry to change the topic, back on! I thank you again
    - Roland
    GM dealer tech since 2005
    '01 Z28 LS1/T56
    t-tops
    stock 241 heads, stock cam,
    stock muffler, factory wheels

    8.2 @ 86
    (1/8th mile with 255 Toyo Proxes)
    I am learning...

  15. #15
    Also, I would like some more info on adding a flex fuel sensor to the car. Lt1z350, Can you pm me the info like what sensor to use and the pin on the ecm?

  16. #16
    Accidentally deleted my post.

    A lot of great info on here, I did not want to do the cams but it is my friend vehicle and he wanted to buy them. I told him to hold off on it and save the money for a better turbo when it's available. Right now the car was running fine but after removing the stock muffler and adding a borla it started cutting throttle but not as harsh. I am thinking exhaust back pressure might have dropped when the factory muffler was removed. We brought down the boost to 18-20 psi and dynod some good numbers but I was surprised it was so little. It did 223 whp and 254 torque. The power was going up but since the tcm is not tuned, the car shifts at 6200. Would it be a good idea to bring the shift points higher? We are ordering the unlocked tcm from HPT sometime this week.

  17. #17
    Tuner in Training
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    This is very nice tips here. Many thank you's for information. I too struggle with 17 pcm and throttle close when adding more power.

    Quote Originally Posted by Vasquezz1228 View Post
    Accidentally deleted my post.

    A lot of great info on here, I did not want to do the cams but it is my friend vehicle and he wanted to buy them. I told him to hold off on it and save the money for a better turbo when it's available. Right now the car was running fine but after removing the stock muffler and adding a borla it started cutting throttle but not as harsh. I am thinking exhaust back pressure might have dropped when the factory muffler was removed. We brought down the boost to 18-20 psi and dynod some good numbers but I was surprised it was so little. It did 223 whp and 254 torque. The power was going up but since the tcm is not tuned, the car shifts at 6200. Would it be a good idea to bring the shift points higher? We are ordering the unlocked tcm from HPT sometime this week.
    I am no expert by far on the LTG. I am learning like many. What I have noticed though, the LTG seems to not like such high RPM. Power seems to drop swiftly after 5900 RPM. I try to keep shifts less than 5900rpm. I attempt to scale each gear down. Example: 5900, 5800, 5700, 5700. This had worked for me, but other tunes may respond different on LTG. Stock turbo seems to run out of steam up high.

  18. #18
    Tuner Boost's Avatar
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    Quote Originally Posted by Boost View Post
    That is wonderful information and option. I thank you. Currently just wanting to add an extra 20 hp to a stock 1.5 on pump gas and did not want to chase my tail on boost as I did in my prior 1.4t and LHU. Should be simple enough but as the controller and engine is new I've been stalking this thread and others, looking for hints. Sorry to change the topic, back on! I thank you again
    turned everything up (lol) but still stock levels. did not touch wastegate table is that what's lacking? just looking for a tiny bump that can be felt
    - Roland
    GM dealer tech since 2005
    '01 Z28 LS1/T56
    t-tops
    stock 241 heads, stock cam,
    stock muffler, factory wheels

    8.2 @ 86
    (1/8th mile with 255 Toyo Proxes)
    I am learning...

  19. #19
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    Quote Originally Posted by Emily89 View Post


    I am no expert by far on the LTG. I am learning like many. What I have noticed though, the LTG seems to not like such high RPM. Power seems to drop swiftly after 5900 RPM. I try to keep shifts less than 5900rpm. I attempt to scale each gear down. Example: 5900, 5800, 5700, 5700. This had worked for me, but other tunes may respond different on LTG. Stock turbo seems to run out of steam up high.

    I know the 1.4 in the Cruze DEFINITELY runs out of steam with the stock turbo before even 6k RPMs. Seems like the little bastard is done working "efficiently" at just 5k-5500. Lol.
    2012 Chevy Cruze 1.4T A6

  20. #20
    Tuner Boost's Avatar
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    Both tuned and unturned, torque drops rapidly at 5000 rpm on the 1.4
    - Roland
    GM dealer tech since 2005
    '01 Z28 LS1/T56
    t-tops
    stock 241 heads, stock cam,
    stock muffler, factory wheels

    8.2 @ 86
    (1/8th mile with 255 Toyo Proxes)
    I am learning...