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The Chuggle is real!

33K views 108 replies 38 participants last post by  Englishguy3012 
#1 ·
Hello everybody,

I wanted to post a thread regarding my personal findings on the whole chuggle/studder issues with the 15/16 Colorados.

As many of you, I also experienced severe chuggle at low RPMs with my 2016 Colorado Z71 Crew cab.

The first thing I tried was the Trifecta tune. As many of you reported on this forum, the chuggle eventually found it's way back. Then, here it came the famous Pedal Commander. While it severely reduced my pedal lag, at low RPMs, there it was the chuggle. The commander helped get rid of it by downshifting with less foot movement. The studder still annoyed me however. After the PC, I purchased the Diablosport Intune. I tried several settings there, nothing helped since after a while, the truck returned to it's old habits. Then, since I had the tuner already, I got with Jerry from BNR. He provided me with a custom tune and even changed raised the mph setting where the truck would upshift to reduce the chuggle. The custom tune helped a lot but the chuggle had a great comeback again.

You wonder why I am writing up all this boring stuff... Well, I think we all were looking at the wrong responsible party for the chuggle here. All the above tunes/mods helped greatly but the only thing that got 100% rid of my chuggle was switching to high octane fuel. I used 87 for all above experiments. I know, many of you stated on the forums that it absolutely should have nothing to do with the transmission performance, however, from my experience I believe that the ECM is "making" the truck chuggle. Let me explain.

As in the article I found on the BNR website (http://store.badnewsracing.net/Which-fuel-should-I-use-in-my-LUVLUJ-Does-it-matter_b_1.html), newer GM engines have an interesting self defense system, where they pull timings to prevent engine knock and/or detonation. Low octane gas is more susceptible to than high octane, especially in warm weather ( I live in FL). I personaly believe that the "TCM relearn" we experienced with the tunes is actually the ECM adjusting to the fuel after the programming. Some trucks may have a more aggressive adjustment to the point that it makes the engine chuggle at lor RMPs.

I have no idea why some Colorado owners don't experience the same chuggle but I bet that the RPMs at upshift are the same for the non chuggling truck vs the chuggling trucks. The variation in ECM adjustment to gasoline type might be different for some of us to the point where 87 does not produce enough power to keep the engine smooth at low RPM but 93 does. I am the living experience with some others on this forum that reported no chuggle with high octane.

In conclusion, on some trucks with the famous chuggle, you either need a tune that will keep the gears much longer before upshift (BNR has it) to prevent low RPMs with 87 octate or switch to 91 or 93 and enjoy a chuggle free experience. Please note that it took me two fillups with high octane to completely eliminate the issue.

Let me know what you guys think, enjoy your day!
 
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#2 · (Edited)
Thanks for this input. And. . . it does make sense including how it would take abut two tankfuls to see improved results.

From what you say, it does make sense that the ECM is trying so hard to maintain a lean mixture that at low RPMs it causes the engine to slightly lug and causes predetonation and the ECM then tries to correct it.

I am also wondering if a good quality real time OBD II scanner might be able to log and see what the knock sensor input to the ECM is at the "chuggle" point and also if spark is then going to retard?

Just a thought. I am wondering also, if the "chuggle" is more predominant in locations where altitude is different? It would be interesting to maybe start a poll and have owners post if they are in higher or lower altitudes. The amount of oxygen the ECM sees also may affect chuggle.
 
#3 ·
OP, I posted the same theory awhile ago in another thread. I say "theory" because I didn't bother actually testing it out with higher octane fuel. Anyway, someone said it was wrong because diesels have the chuggle too. I don't know if that's actually true.

How many tanks have been "chuggle free" for you now that you've starting using high octane? I'm wondering if it may come back over time like it seems to do with a tune.
 
#17 ·
When I decided to give this fix a try, I ran the 87 tank empty. I have about 20K miles on my truck. Then I added one bottle of fuel system cleaner with 10gal of 93. Once I ran that tank empty, i filled up all the way with 93, I am about 3/4 full with that tank.

I was very skeptical trying this "fix" but for me it worked! I also noticed a small increase in MPG. I can't say for certain how much until a few more fillups. I am also very curious if there'll be a great hesitation comeback, I will certainly update you guys on it.

The 87 here in my town now goes for 2.49 and the 93 is 2.99. On a full tank (i think I pumped 18 gal last time) that is $9 difference. It would take about a 3MPG difference to make up for the cost but I am aware that I most likely will not see such a drastic difference. At this point I am so pleased to have my truck chuggle free that I gladly swallow the cost. We'll see later on.... I also worry that it's just simply not good for the engine to hesitate.

For those of you who mention driving style, I don't think it is justified to have an engine hesitate just because you are light on the accelerator. On my way home I turned off my Pedal Commander (I know some of you probably will say Why??? :smile2: ) but I really wanted to feel the low RPM performance and it is night and day. I guess I had a really bad version of the chuggle before the 93.

Just try it, a couple of tankfulls will not hurt anything! Or will it? (you won't want to switch back :smile2:)
 
#4 ·
Yikes! I'm going to give the higher octane a try. I'm at sea level on the Jersey shore and have the chuggle as well. It's not consistent, but is there maybe 50-60% of the time during easy acceleration. Truck is almost one year old -- no tunes or engine mods.
 
#5 ·
...

I have no idea why some Colorado owners don't experience the same chuggle but I bet that the RPMs at upshift are the same for the non chuggling truck vs the chuggling trucks. The variation in ECM adjustment to gasoline type might be different for some of us to the point where 87 does not produce enough power to keep the engine smooth at low RPM but 93 does. I am the living experience with some others on this forum that reported no chuggle with high octane.

...
First, not going to dispute any of your thoughts, but my take on this specific question you raise has to do with driving styles. It would probably be hard to quantify, but I am going to assume that the majority of you who see the "chuggle" effect would probably be classified as an aggressive driver versus a more laid back driver.

In day to day driving, I rarely see a problem. Last night, I had to be at an appointment at our church for 6 PM. Left Fort Worth a few minutes after 5 PM, should be no problem, but I failed to take into account that the Fort Worth Main Street Festival is this weekend and they have already closed off half the streets in downtown. Traffic was horrendous as people tried to jockey around all of the street closures on top of all of the construction. So, I wasn't thinking about hyper-miling my way to my destination, but was driving much more aggressively. I noticed a lot more of an issue with chuggle.

Not saying that a driving style is right or wrong, but rather, these trucks, and a lot of the newer designs, are programmed to lean toward a hyper-mile style of driving to maximize the MPGs and the more aggressive driving styles do not match up with the program.

I don't see enough of an issue to pay the extra $$$ for higher octane. I did try a couple of tanks of "real" gas without any ethanol, didn't notice any change, but I was towing a trailer, so might not have been noticeable. I also tried some higher octane a couple of times when it was priced similar to Regular, couldn't tell a difference in one tank.
 
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#16 · (Edited)
I think you may have it backwards, I am sure I would be considered an aggressive driver and my truck has never chuggled. I do however run 89 octane gas most of the time and occassionaly use 91 octane if fuel prices are under or close to $3.00/gal. Which isnt very often here in CA. I thought the chuggle might be from people trying to hyper mile. I even tried to get my truck to chuggle on my way home today at 40 MPH in 6th gear, I hit the throttle and RPMs instatntly go up to about 3500, truck accelerates as it should. So it is either an issue with some and not others or it could be octane related, maybe 1 day I will try 87 octane and see if that makes it chuggle.
 
#6 · (Edited)
Fuel quality seems like a plausible factor in the exacerbation of the chuggle issue. It would be interesting to see if owners at higher elevations have less problems with this issue, as the thinner air at higher elevation reduces power, but it also reduces octane requirement for naturally aspirated engines. Most cars and even my liter class sport motorcycle, run happily on the basic 85 octane gas here in thin air land Denver.

I have a diesel, so it is the same 6 speed tranny and completely different engine. It does hold onto 1500 rpm in 6th gear a little more than I would like, but the diesel deals with that and a slight increase in throttle move it off that zone with a downshift, and it seems to be getting better with mileage - my truck only has 1300 miles on it. My driving style is a little "jackrabbity" dipping into the pedal and getting to cruising speed fairly quickly, so maybe it is "learning" to deal with my semi leadfoot ways.

I could see any gas engine struggling if the trans kept it at 1500 rpm with any kind of a load on it. I have to try to make it do it, but even my Toyota Camry can be made to chuggle if the gas pedal is carefully manipulated in the right way - but you really have to almost want to make it do it. That car releases the higher gears very easily when confronted with a hill or more gas pedal.
 
#7 · (Edited)
The chuggle problem is real. Switching to high octane helped a lot for me (Im at sea level), but the issue still shows up randomly, mostly with highway traffic (not day to day traffic light traffic). I dont know why. I wish GM would investigate the issue and release a statement or if they refuse to, then be forced to do so through the courts.

Im more pissed about higher fuel costs through premium fuel vs the chuggle honestly. I feel consumers should have been told that the truck does NOT function as advertised without premium fuel and that the true MPG or $/mile comparables between other trucks are not what they seem...............

I dont spend that much time on the highway. Perhaps if I had a big highway commute it would be a different story. I will start doing a lot of highway driving this summer and will report back.
 
#8 ·
91 octane and the PC solved my chuggle problems. The 91 octane alone almost cured it. The PC fixed the reluctance to downshift in slow speed situations, most notably long, slow speed left turns at large intersections. During these left turns it used to shift into third and sometimes fourth and then refuse to downshift unless I floored it. Not now.
 
#10 ·
I recall what you all call a chuggle on my truck a few times I guess. I think it is VERY simple, the trans likes staying in a high gear and likes to keep the torque converter locked up. There is no doubt in my mind that this is NORMAL being it was designed to do this. Also there is no doubt in my mind it is programmed to do this for increased MPG. I know some will say it's not "normal" because it's annoying, but still. Think of it this way, it's like driving a manual trans in like 4th gear at 20mph, it does the same thing. I understand for some it is worse than others for many reasons I would guess. Your driving style, type of fuel, quality of fuel, temp of air, elevation, going up hill, shoot even amount of air in the tires could change it! I think it is as close to not being a problem as it is being a problem, right on the borderline. What really, truly stumps me is why many, many people don't like to push the gas pedal. Don't believe me do you? Just go read the pedal commander thread and think about it and you might understand. I guess its possible that my truck is so very special and more powerful than the others that the Pedal Commander was useless and any little "chuggle" doesn't bother me, but I really doubt it. I really think you just need to get used to it and push the pedal accordingly (or let off a little). If you find it chuggling and you aren't wanting to accelerate, let of the gas a slight bit. I find myself looking at the tachometer a lot out of curiosity, and it sits at about 1300 most of its life. I think I might be treating it like a manual trans at those super low rpm times, maybe that works for me, does that make sense? I'm sure this post will probably offend some PC users but I don't want to do that, just want to post what I believe is the "problem". Maybe it will help someone enjoy their great truck. I think the twins are great trucks, I love mine anyway. (even if it likes 1300 RPM) :)
What do ya think?

p.s. I could be wrong (wouldn't be the first time), I wish I knew someone with a horribly chugging twin to test drive, but I don't. Also, it isn't easy trying to fix a "problem" that GM designed into the truck, it's like a dog chasing its tail.
Want someone to blame? EPA

https://en.wikipedia.org/wiki/Corpo...y#Agreed_standards_by_model_year.2C_2011-2025
 
#12 ·
I recall what you all call a chuggle on my truck a few times I guess. I think it is VERY simple, the trans likes staying in a high gear and likes to keep the torque converter locked up. There is no doubt in my mind that this is NORMAL being it was designed to do this. Also there is no doubt in my mind it is programmed to do this for increased MPG. I know some will say it's not "normal" because it's annoying, but still. Think of it this way, it's like driving a manual trans in like 4th gear at 20 mph, it does the same thing. I understand for some it is worse than others for many reasons I would guess. Your driving style, type of fuel, quality of fuel, temp of air, elevation, going up hill, shoot even amount of air in the tires could change it! I think it is as close to not being a problem as it is being a problem, right on the borderline. What really, truly stumps me is why many, many people don't like to push the gas pedal. Don't believe me do you? Just go read the pedal commander thread and think about it and you might understand. I guess its possible that my truck is so very special and more powerful than the others that the Pedal Commander was useless and any little "chuggle" doesn't bother me, but I really doubt it. I really think you just need to get used to it and push the pedal accordingly (or let off a little). If you find it chuggling and you aren't wanting to accelerate, let of the gas a slight bit. I find myself looking at the tachometer a lot out of curiosity, and it sits at about 1300 most of its life. I think I might be treating it like a manual trans at those super low rpm times, maybe that works for me, does that make sense? I'm sure this post will probably offend some PC users but I don't want to do that, just want to post what I believe is the "problem". Maybe it will help someone enjoy their great truck. I think the twins are great trucks, I love mine anyway. (even if it likes 1300 RPM) :)
What do ya think?

p.s. I could be wrong (wouldn't be the first time), I wish I knew someone with a horribly chugging twin to test drive, but I don't. Also, it isn't easy trying to fix a "problem" that GM designed into the truck, it's like a dog chasing its tail.
Want someone to blame? EPA
I think it is your evil, warranty - busting catch can that allows your truck to perform so admirably.

In reality, I think I am in the same camp with you. My RPMs rarely exceed 2000 unless I am in a hurry. I read the Pedal Commander thread, and for the theory of how it works, I am confused: Can't I just re-program my foot to do what the PC does?

The chuggle, hesitation, or whatever you want to call it, is a real item, it has happened to me. But it doesn't rise to a level that I dislike my truck. My truck fills a lot of niches for me, not sure how I did without one for so many years.
 
#14 ·
I understand why people are saying "just push the gas pedal farther". I can only speak to my experience so far. I live in a suburban area in Southern California with lots of large intersections. When turning left it was quite common for my truck to shift into 3rd or 4th by the time the turn was complete. Feeding more throttle in smoothly would result in chuggle and no downshift. Feeding throttle in quickly would result in a delay followed by a downshift to first or second gear. This is not how I want my transmission to behave. When I feed constant throttle I expect the ECU and TCU to determine the best gear for the speed that I am going. This does not happen on my truck. I could trick it into shifting by taking my foot all the way off the gas and immediately getting back on the gas. This would result in a fairly consistent single downshift instead of a downshifting more than one gear. I could also drive around in tow mode and it was much more predictable with shifts and tended to hold each gear a little longer. Of course, shifting manually was an option and worked very well but I grew tired of that. This truck is obviously programmed to stay in as high of a gear as possible. I don't like it and simply re-programming my foot resulted in abrupt downshifts of more than one gear. With the PC I can feed the throttle smoothly and gradually and get single downshifts as needed without thinking about it. For those of you that say you are confused or you just don't get it all I can say is that I (we) are not making this stuff up. This is how our trucks behave. If you were to drive our trucks in our neighborhoods you would experience the same exact things. I guarantee it. After driving with my PC for a week I tried disconnecting it to see if the OEM programming was as bad as I remember. After about two minutes I had to hook it back up. The OEM programming just isn't a good fit for me. That is my story and I'm sticking to it.
 
#15 ·
Here's a recent post from over in the diesel side of the forum:
...
My dad bought a gmc canyon with same duramax along with me and i noticed that his transmission behaves way differently than my colorado's. GMCs is way less responsive.
...
I bring it up here because it's an example of how not every twin drives the same. Just because yours works perfectly doesn't mean anyone who has a problem is "pushing the pedal wrong".
 
#18 ·
Ok....so you've tried 4 different things.... How much time did you allow to pass before moving to something else? Did you give each thing at least 2 months before changing to something else?

I first got the updated transmission program in November 2016. It was nice at first. I would be fair to say - the transmission returned to its old habits gradually but was very obvious sometime in March. That's 4 months.....
 
#20 ·
Actually 5 different things, I forgot to mention that I did get the PIP update in November. About 600 miles later, chuggle. Then it came the trifecta tune. I had my dad visiting from Europe and had to drive to the airport 2 times, about 300 miles and we also went to the beach a couple of times. The chugge came back in probably 500 miles. After that is when I went with the Diablosport tune, honestly with that tune the chuggle never really went away, that is why I got the BNR.

The funny thing is that during the switch to 93, I did not flash any tune and the hesitation resolved. It was also strange to me that the hesitation was more noticeable during warmer days. That observation is what made me think of the ECM vs TCM and gave the high octane a try. I was also encouraged by Jerry from BNR, who pointed out his article regarding the GM ECM self adjusting factor.
 
#21 ·
Interesting about the lower gears and not shifting down. The 6 speed in my Canyon diesel is very smooth, with a slight tendency to hold onto 6th at lower rpm (1,400ish) than I would like, but it shifts readily down from all the other gears. Different engine but same tranny. Ironically, for the diesel, I think GM programmed the same tranny rev it out a little too readily in the lower gears - would actually like it to upshift sooner when accelerating quickly, but not pedal to the metal.
 
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#22 ·
I purchased a new 2016 Canyon SLT CC LB diesel in early February this year. I'm now at 3K miles. I noticed poor throttle response right away and the chuggle issue between 40-50 mph after the first couple of days. Initially I thought these issues would be resolved within several hundred miles as the ECM learned my driving habits. Didn't happen. Several weeks later I found this site and eventually the pedal commander thread. I purchased one about 4 weeks ago and I'm now driving a different truck. It's adjustable on the fly so you can play with it and dial in your favorite driving style. It exceeded my expectations and is worth every penny I paid. No affiliation with Pedal Commander and no interest in debating whether or not this product works like you will see on the Pedal Commander thread. If you are dealing with chuggle or slow throttle response simply buy one and try it. If its a fit you you won't want to be without it. If not you can send it back for a full refund. End of discussion. Over and out!
 
#31 ·
I actually own a PC and it does address one of the issues, which is a very insensitive gas pedal; however I got tired of always getting the truck to downshift because of the hesitation. The chuggle was still there but it was easier and more satisfying to press the pedal less in order to get a downshift. Driving high octane with the PC on city mode is a dream come true!

How about #6 - did you drive in Tow/Haul mode for an extended period of time?

I personally refuse to buy higher octane gas. Seems, no matter what you do or try, the transmission adapts to that eventually. It's almost like you gotta do something totally drastic every 2 months just to 'confuse' the programming.


I did try Tow/Haul mode, not for extensive period because when coming to a stop, the downshift is quite aggressive from 3rd to 2nd. For some reason it jerks my truck. I also noticed less MPG driving like that.

It does take 2 tanks to adapt. The ECM has a high and low octane timing table, and as it runs longer with less knock events consistently on high octane, the timing advances further consistently. With 11.5 : 1 compression, I can't see how they not recommend 91 for optimal performance, but able to to run 87.

I 100% agree, I was thinking after some time to try 91 and see if it'll be still chuggle free.. It is a bit cheaper than 93. I think I'll figure out a good average MPG first with 93 with a few tanks used.
 
#23 ·
Over at Equinoxforum.net, there was a gentleman that posted about the LFX engine in regards to how the engine was designed for high octane by the engineers but marketing needed to be able to sell the engine as 87+ The PCM's software was written to retard the ignition timing for 87 octane. The engine would relearn the mapping after a couple of tanks of high octane. I have experienced this with my LFX in an Equinox. I started out buying high octane when I first got it but with mostly short driving, I got tired of paying the extra cost. I will be switching back to high octane before we take it on a long trip in June across the plains and into the Rockies as we will be loaded down pretty good. The OP is most likely correct in what he is experiencing with a couple of tanks of high octane.

Here is the link to the discussion: EquinoxForum.net: HFV6 Octane Rating It mentions that this has been also discussed on the Camaro sites in regards to their LFX.

GM is coming out with a 2.0 turbo for the 2018 Equinox & Terrain vehicles that do require high octane.
 
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#24 ·
Thanks for the octane idea. Will try it starting tomorrow.
 
#27 ·
My understanding is that it takes a tank or two for the PCM to relearn/adjust the mapping. I will know more next month when I get ready a tank or two before our trip to the Rockies on a 13 hour run. :smile2:
 
#29 ·
Ha... I just posted about this yesterday. With the "chuggle" I believe the engine is actually misfiring; at least that what mine is reporting in the ECU. And when I ran a couple tanks of 91 through it while on a trip in Florida the problem went away. It was doing it since the first week for me, so it's not gotten gummed up, or something "gone wrong" it's been wrong since day one.

To bad GM doesn't own up to the issue... With all the electronic controls now a days, there has to be something they can tweak.
 
#35 ·
Why on earth does it do it with the gas and diesel? What about the 4 cyl? ANYONE with the 4 cyl and auto have a chuggle problem?

Is everyone smoking crack? Am I smoking crack and just not know it? :surprise:
 
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#47 ·
Anyone run with 104+ octane boost?
 
#48 ·
My 2008 Impala SS with the 5.3 V8 would run on 87 but the manual said you could experience diminished performance. Said 91 was preferred. I ran 89 because I'm cheap. I may have missed out on some mysterious performance. So there's a Naturally aspirated GM asking for 91 octane.


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