Large idle surge when coming to a stop

[bk2life]

No i don't have a log/tune to post yet.

I normally deal with gen3/4 stuff.

I am asking for help on what to scan in order to post a quality log here to help figure out my issue.


This vehicle has been tuned 3 years ago and for some odd reason has in the last 6 months or so started this huge leap/surge in rpm when coming to stop.

I know what i would look for and how to set up the scanner for earlier engines, but asking for help with this gen 5 engine.

When driving down the street lets say 45mph street light turns red, you slow down not hastily, just normal driving, when you get to about 5mph the engine will shoot up to about 2000 rpms like you blipped the throttle. Now if youre close to the person in front of you, you can hit them if youre not careful. The idle will the surge again and engine usually dies.

This does not happen on every deceleration, but its common enough i have to be cautious when coming to a stop.

Other than deceleration, any other time this big idle surge is not there.

2014 5.3, decent sized street cam, no AFM, head/exhaust work, 6.2 intake/throttle body etc.

Thank you for any help on what the gen 5 needs in the scanner to get a correct log to look at.

[edcmat-l1]

This should be most of what you need.

E92.E90_throttle control.Channels.Channels.xml

[bk2life]

This should be most of what you need.

Nothing else?
throttle cracker?

[edcmat-l1]

Nothing else?
throttle cracker?

Did you post a data log?

[bk2life]

Did you post a data log?--

No sir, not yet, i was asking a follow on question. Since you posted '-This should be most of what you need' I just didnt want to waste anyones time if there is more i should be logging right from the start.
Thank you

[bk2life]

here is a log with it dying and another log with driving around, no engine stalls, but a couple of times it was close.

[edcmat-l1]

Looks like the DFCO settings have been changed maybe. It pegs the trims on the decel. Being overly rich leading up to the stall is going to be a main contributor.

The minimum base spark has been set to positive numbers at idle. That's typical of someone who doesn't know how to dial one of these in. I have a couple local tooners here that do the same thing. Need to put that table back to stock and figure out what's wrong that that was supposed to "fix".

Doesn't look like much has been done with the VVT.

Greg will have more input. He's the resident GEN5 smart guy.

[bk2life]

That's typical of someone who doesn't know how to dial one of these in.

this was dyno tuned by nicD a few years ago.

I have had almost no issues until recently this big surge that almost puts me into the car in front of me.

[edcmat-l1]

this was dyno tuned by nicD a few years ago.

I have had almost no issues until recently this big surge that almost puts me into the car in front of me.

I don't care who did it and when, that table set the way it is, is a quick and dirty way of keeping it from going into negative timing at idle. It is a sign the person who tuned it could not get it to idle properly, return to idle properly, have decent to normal idle quality, etc. If you want to know how well the rest of the tune is dialed in, put that table back to stock.

If you're familiar with GEN4 stuff, the condition you're describing is typical of BRAF being too high, throttle follower being goobered with by someone who doesn't know what they're doing, etc. It's an idle flare after a downshift. That being said, I can't tell you there's a silver bullet fix for it in this. It is most likely a combination of things all revolving around idle torque control.

All that being said if it came to me to fix this problem a bunch of it would need put back to stock and start by dialing in the VVE and VVT.

[GHuggins]

The 40% fuel addition on decel is oxygen storage for cats. To kill that there are basically - depending on the OS - up to 22 different background settings that need to be changed to do it right. You can flip one switch, but really they all need to be done. The left side of your adaptives tables should never be more negative than the positive side either. For it to be doing it sitting at a light then more's wrong and probably just something that has learned or been skewed from incorrectly flashing the cal when it was cold out or whatever like that. Your VE doesn't look like it's dialed in and your torque model is definitely wrong. The map side being too high will cause the throttle to want to stay open, which will cause the whole tune to be off.

[edcmat-l1]

The 40% fuel addition on decel is oxygen storage for cats.

Hate to argue with you Greg but, no. And here's why.

1, Cats don't store O2 on decel they release it. And that activity doesn't increase O2 storage it uses it up. During that time it's stripped all the stored O2 from the cats and effectively turned them off for a period of time.

2, In the OP's data log, where it does this, the result of the added trims is INCREASED emissions, not reduced. It is the complete opposite of what's intended.

3, It's not due to cat over temp protection as the commanded stays at 14.14, not to mention the load is not great enough for cat OT to run.

4, It's not due to intended NOX reduction as they don't produce NOX on decel the combustion temp isn't high enough.

It just doesn't make sense. It goes everything I've ever learnt and know about emissions and catalyst operation so I had to wrap my head around and then go digging through my data log files.

Here's what I got. First screen shot is the OP's. Keep in mind when his does this it holds it for 13 seconds!! It's not a quick blip. It's in closed loop and it does NOT respond to the O2 sensors. It does NOT try force them back down.

2014 Silverado OPs.jpg

Here are just a few of mine. All various GEN5 vehicles all of them modified. Cammed, supercharged, whatever. NONE of them AT ANY POINT do what that thing does.

2015 Corvette.jpg

2019 Camaro stg 3.jpg

2016 Suburban Supercharged.jpg

2017 Silverado stg 2.jpg

2017 SS Supercharged.jpg

I looked through many more just got tired of taking screen shots. I can lots more. All look the same.

Not only do they NOT look like the OPs they all look IDENTICAL in operation. NONE of them max the trims except when it comes to time to trigger the O2 into action.

That 13 seconds of time where it pegs the trims, goes pig rich is not by design. The vehicle would fail an IM240 test. 13 seconds of highly increased HC and CO is NOT the intention there.

[GHuggins]

It dumps the fuel to light off and burn off the oxygen. When cats are removed all the rear O2 sensors see is the oxygen during decel from fuel cut, so it dumps the fuel to do what it's programmed to do. Burn off the excess oxygen that happens naturally on decel. Happens everytime the cats are removed on these. These will also run routines for pre cat O2 verification and fuel control using the rear O2's inputs. Why it is imperative that if you don't know how to do it, to never remove the rear O2's on one. I see this all the time with gen V's. Change the background tables and she'll even idle richer or more in line with your wideband. What I always see anyway. I'm also currently seeing hpt updates where you have to read from internet wiping out background changes and why some people are seeing problems they didn't have before.

Now with his surging and all of that because of it, well that's just his tune not being setup to handle stuff like that correctly.

[GHuggins]

Screenshot from one that another tuner was asking me about as he hadn't seen it before either. Looks the same right except for his is set up to handle it better? Most of the cars won't do this until the newer year models. Nearly all of the trucks do though.

Same thing.jpg

[TriPinTaZ]

Screenshot from one that another tuner was asking me about as he hadn't seen it before either. Looks the same right except for his is set up to handle it better? Most of the cars won't do this until the newer year models. Nearly all of the trucks do though.

Same thing.jpg

I can attest to Greg's experience.

I definitely started seeing this on 2022+ Camaro's. The older ones don't do this and none of the C7's do this. You will get the same behavior if you unplug the rear O2's, even if you disable all of the DTC's.

[GHuggins]

You will get the same behavior if you unplug the rear O2's, even if you disable all of the DTC's.

Funny enough, I actually had a very long discussion with a car harness company owner about this a couple of nights ago over the phone because he was removing the rear's off of some of the harness's. He wasn't aware of this either and after talking to him about it, he was like that actually explains some things he had been seeing on a prototype vehicle of his and is now wanting to do a warning vid about it so people are aware of what altering certain things with these newer platforms can cause. Takes a whole lot more than just killing dtc's to get around this. I was just fortunate enough to talk to the right people myself that filled me in on it.

The OP's cal has the cats killed but all other corresponding test are still enabled. Test seem to prioritize over the component settings. So set it to not have the component only and the test and other operations will still run as if it was still there. Only way to do it right is to remove the component then kill the test along with some other corresponding operations that pertain to it. I found all of this out the hard way. AND this is for off road operations only of course Otherwise, the best option for everyone else is to leave the cats and learn to tune around them, which can be VERY hard at times on its own.

[TriPinTaZ]

Funny enough, I actually had a very long discussion with a car harness company owner about this a couple of nights ago over the phone because he was removing the rear's off of some of the harness's. He wasn't aware of this either and after talking to him about it, he was like that actually explains some things he had been seeing on a prototype vehicle of his and is now wanting to do a warning vid about it so people are aware of what altering certain things with these newer platforms can cause. Takes a whole lot more than just killing dtc's to get around this. I was just fortunate enough to talk to the right people myself that filled me in on it.

The OP's cal has the cats killed but all other corresponding test are still enabled. Test seem to prioritize over the component settings. So set it to not have the component only and the test and other operations will still run as if it was still there. Only way to do it right is to remove the component then kill the test along with some other corresponding operations that pertain to it. I found all of this out the hard way. AND this is for off road operations only of course Otherwise, the best option for everyone else is to leave the cats and learn to tune around them, which can be VERY hard at times on its own.

And I was fortunate enough to speak with you, who pointed me in the right direction with User Defined Parameters(which solved the issue). HPTuners doesn't expose the tables necessary to solve this, and they likely never will.

[bk2life]

leave the cats and learn to tune around them, which can be VERY hard at times on its own.

This vehicle has a cam, long tubes hihg flow cats and a full exhaust. What it doesn't have is rear O2s.
I have no issue with installing rear O2s if it will help with the overall tuning.

[edcmat-l1]

Well guys chalk that up to you learn something new everyday. To me it goes against everything I know and have been taught concerning catalyst operation and closed loop fueling. It makes no sense to intentionally cause an overly rich condition on decel. From the beginning of emissions they've all taken this period of operation to essentially cut the emissions to zero.

That being said, one of the reasons I maybe have not seen this is I build late model stuff with cats and rear O2s always. I'm sure some have seen me preaching on here about it. I also encourage the shops I work for to build cars the same way.

I'd be interested in seeing what it does if the DFCO settings were put back to stock. Even with what y'all are saying, I bet the DFCO settings have something to do with it.

[edcmat-l1]

OP, if you would, flash this and take it for a long data logging. Only thing I changed are the DFCO settings. I'd like to see what it does just changing this only. If you don't mind.


jamie silverado 2024_DFCO_EH1.hpt

[GHuggins]

It will most likely do it till he puts the rear O2's back. Something about the routines where it can't see the oxygen via the rear O2's, it'll assume it's got too much and on decel lots of oxygen is going into the cats, so it'll dump the fuel.

I can actually post up another log where an owner only installed an L8t cam in his l83 if you need me to. It's doing the same thing. He has one O2 removed for the wideband. They've got super stringent about the emissions bs and cat life to the point that they don't care so much about the emissions during these times so as to keep the cats doing their jobs. Heck, they'll even use post cat O2's for fuel control if necessary. First time I had seen that. They've been using them for redundant self checks of the pre-cat O2's since the early colorado's and trailblazers that I can confirm, but I didn't realize the fuel control part until one bit me in the arse...

I also agree with you 100% Ed. I wouldn't have ever thought about them doing this "for emissions" either. Goes against what most of use were taught

BUT, the OP's still needs to be setup to handle stuff like this on top of getting the rear O2's back in, which sometimes requires sacrificing other "wants" for drivability. It's just interesting that he hasn't noticed it before now.