Large idle surge when coming to a stop

[TriPinTaZ]

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.

I think there is some test routine that gets stuck trying to run over and over when it doesn't see the rear O2's. I'm not sure of the cause but even with stock DFCO settings it was happening. It only started when I removed the rear O2's which I only did because on the Camaro's, the ARH headers don't have a 5th bung for the wideband like the Corvette Systems do. Once I used User Defined Parameters to change some tables, that are not exposed by HPTuners, the issue stopped.

[edcmat-l1]

OK so just to clarify, the 13 seconds of decel is NOT normal behavior, it's a side effect of removing rear O2s and/or cats. That makes sense. I was interpreting Greg's initial comment as "yeah that's normal".

I'd still like to see a data log of it with JUST the DFCO settings put back to stock. To satisfy my curiosity. Because they're changed I'd have to eliminate it as a possibility.

[TriPinTaZ]

OK so just to clarify, the 13 seconds of decel is NOT normal behavior, it's a side effect of removing rear O2s and/or cats. That makes sense. I was interpreting Greg's initial comment as "yeah that's normal".

I'd still like to see a data log of it with JUST the DFCO settings put back to stock. To satisfy my curiosity. Because they're changed I'd have to eliminate it as a possibility.

In this log export you can see it happening. The STFT's go full rich and then the throttle blade keeps opening up, which I assume is because the timing is getting pulled down into the negatives. Lambda reads way rich as well. The DFCO settings on this car are stock in this log.

o2issue.hpl

[GHuggins]

OK so just to clarify, the 13 seconds of decel is NOT normal behavior, it's a side effect of removing rear O2s and/or cats. That makes sense. I was interpreting Greg's initial comment as "yeah that's normal".

I'd still like to see a data log of it with JUST the DFCO settings put back to stock. To satisfy my curiosity. Because they're changed I'd have to eliminate it as a possibility.

Well, it's 100% normal - as in a designed in algo - when you remove stuff or have a component failure and have the cal incorrectly set up for it, so yes, in that regard it's completely normal operation for cat storage and protection.

[edcmat-l1]

In this log export you can see it happening. The STFT's go full rich and then the throttle blade keeps opening up, which I assume is because the timing is getting pulled down into the negatives. Lambda reads way rich as well. The DFCO settings on this car are stock in this log.

o2issue.hpl

Yep looks the same. And commanded EQ never changes. That's pretty crazy.

[bk2life]

OP, if you would, flash this and take it for a long data logging.

yessir, no issues. I can do it tomorrow as i have a long drive to go pickup an adapter.

It's just interesting that he hasn't noticed it before now.

This is what my concern was. In the 3 years since it was tuned, 2 years since i have been home from iraq and able to drive it, i have never had this flare up. I dont know if i described it well, but youre driving down the road, light turns red, you slow down, stop, and almost as you hit zero mph it flares up like your hitting the throttle tryin to show off to the guy next to you. But if youre not paying attention, the vehicle will leap ahead like 3 feet.

It'll be a week or two before i can weld up some bungs in the exhaust for the rears..

I'll upload what edcmat asked for and I'll be back with the scan results.

Thanks again for the help.

[Alvin]

Are you sure it isn't a downshift timing issue? If the downshifts aren't timed good coming to a stop the 2-1 will give you a big lurch just like you are describing.

[bk2life]

here is a log from this morning.
seemed to take forever to warm up ECT

cruise.hpl

[bk2life]

Are you sure it isn't a downshift timing issue? .

im not sure at all, but i will look closer at my logs to see if this is what is happening.

I noticed my spark drops every shift accelerating

[edcmat-l1]

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.

That's what I said on the first page.

here is a log from this morning.
seemed to take forever to warm up ECT

Sounds like it has a 160 stat in it. I'd put either a stocker back in or at least a 180-185.

And yeah it's still doing the fuel trim thing on decel.

[bk2life]

And yeah it's still doing the fuel trim thing on decel.

What do you suggest the next step is?
adding the rear o2 back in?

[edcmat-l1]

What do you suggest the next step is?
adding the rear o2 back in?

The tune needs a lot of work but the first thing I'd do is put downstream O2s in it and get rid of that rich-on-decel situation. I don't like that. That is if it has cats on it. If it doesn't it's pointless, unless you put cats on it.

[GHuggins]

Might need to write entire....


Fix your other idle settings. Even if it's downshifting, it shouldn't flare. 5.3's are usually pretty easy to tune for a cam as long as you're correcting the torque model right. That requires your VE to be REALLY REALLY close. Otherwise, I would fix that for you too.

[bk2life]

write entire.....

I did this morning. idles around 1200 rpms -- feels like a lazy throttle now [ like a carb with bad timing] --at the very end i use controls and set timing to 700 to get it to idle

here is a log driving around the block.

silvia new upload.hpl

[GHuggins]

Well again, this corresponds to how much difference having one thing right can make with everything else. Now your engine knows it doesn't have those and it's completely changed the fueling and torque output. If you notice, your super rich decel is gone too.

You're still not logging what you need to be for me to know the state of your VE table. You need maf and VE airflow for that. If you can show your VE table is right I can fix your map torque model and rough in your airmass model to get drivability and idle timing back near stock. I'm willing to bet you didn't set your base temp when you wrote the cal either??? Odds are your VE are possibly out of whack now.

Perform a throttle clean reset then double check your VE.

[bk2life]

You need maf and VE airflow for that. .... you didn't set your base temp when you wrote the cal either??? ......Perform a throttle clean reset then double check your VE.

I really know nothing of GEN 5. I paid to have what i was told is one of the best gen 5 tuners around me.
I can log whatever you ask. I was logging MAF and dynamic airflow, are these not what you are reffering too?
Base temp, its set at 68 degrees. This is the first i have heard of base temp. I dont know what it does, but after this post i will google and learn.
I'll do the throttle clean reset and go for another log once i know what you would like me to scan for you.
Also, thank you for looking at this. If you want funds for helping, just message me, I don't expect anything for free.
Time is valuable.

[GHuggins]

MAF g/s airflow and VE g/s airflow. People don't know this and I had to find out the VERY hard way, but base temp needs to be set to ambient temp anytime you flash the ecm. They just take for granted that most shop temps where the flashing will occur is around 70 degrees IMHO... I chased VE fueling changing issues for about a month straight this last winter until I figured out it had to be set when flashed to whatever the temp was at the moment of being flashed. Bit of a pain, but after figuring that out, my VE corrections for remote tunes have stayed within 4 or 5 % flash to flash.

I use this to dial in the VE... It just makes the VE airflow the same as the MAF airflow. This is a version of Cringer's formula just I'm using MAF airflow instead of dynamic.

(([16.71]+([16.71]*([50116.156]/100))-[2311.71])/[2311.71]*100

You can use this filter to dial in the MAF.

[50010.241]>80 AND [6215.241]>57 AND [6215.241]<74

Then this filter for the VE. Just make sure to set the base temp...

[50010.241]>86 AND ABS([50040.71]-[50040.71.shift(-10)]) < ([50040.71]/[50040.71.shift(-10)])*0.1 & ABS([2311.71]-[2311.71.shift(-10)]) < ([2311.71]/[2311.71.shift(-10)])*0.1 OR [50090.156] > 95

These are all basically the filters and formulas posted by others that I've slightly modified.

Once your VE and MAF are dialed in repost the cal with the corrected VE and a corresponding log. You didn't have a different tb or anything like that did you? I might need to fix that for you first if you do since I do have yours defined.

[bk2life]

ou didn't have a different tb or anything like that .

yes i have the 6.3 intake and throttle body on my 5.3
I forget what i had to change now, but intake size, throttle scaler, and i think something else. I'd have to do a compare to remember. But this was 8 months ago, probably longer when i changed them.

And thats really odd the base temp when uploading

[bk2life]

I tried adding the maf ve to the log, but i must have not paid attention to what i was doing, as the log was stuck on 95 of the map

here is a log, useless, but i own my mistakes.

idle maf ve.hpl