ZL1 STFT high on decel

[VodeAn]

I'm working on a modified 2015 Manual Trans ZL1 with an odd issue.

When coasting to a stop the STFT suddenly shoots to +29% and makes the car run rich, causing the idle to surge.
Tried running in speed density only, maf only, and blended setup. Also tried with LTFT on and LTFT off, same issue every time.

Has anyone ran into this issue before? Is there a fix for it?

Attached is the log, tune and cfg.

Thanks

Attachment 59665
Attachment 59666
Attachment 59667

[VodeAn]

You can see the problem at 5 min and 4 seconds in the log

[SultanHassanMasTuning]

injectors?

min inj pw

[schpenxel]

Your VVE table drops off a cliff under 40kpa. I'd at least try bringing those areas back up to more closely align with the surrounding areas first


VVE CLIFF.JPG

[dreksnot]

I've been battling the rich on coastdown issue too. Would like to know what approach to take.

[schpenxel]

Wonder what fuel trim cell # you guys are in during the rich coastdowns?

[JBZ]

so stupid question and feel free to screen slap me here . but isn't DFCO supposed to be taking fuel out on decal...unless you have it disabled of course. sorry guys.

[schpenxel]

It should--I've seen mine max out the WB lean when it kicks in

[JBZ]

It should--I've seen mine max out the WB lean when it kicks in

that's what mine does...O2's stop swinging. i can tap the throttle when its doing it and they will start swinging again normally.

[dreksnot]

so stupid question and feel free to screen slap me here . but isn't DFCO supposed to be taking fuel out on decal...unless you have it disabled of course. sorry guys.

The DFCO is getting sidetracked. Yes, it suppose to when meeting the conditions. So, without any consideration to DFCO (had it disabled when tuning fuel), want to focus on how to eliminate the rich on coastdown issue, please.

[dreksnot]

injectors?

min inj pw

Second or third time I've heard of Min IPW as a culprit. So, how to approach troubleshooting/fine tuning. Right now, per ID-1000 data, Min IPW is 0.125ms. Reduce this to something like 0.120? 0.124? My fueling appears good, at least, to novice eyes.

[schpenxel]

Make it 0 for testing purposes. Don't think that's it though.

[DSteck]

Engine
->Fuel
--->Open & Closed Loop
----->LTFT Idle Cells Thresholds

Set Enable VSS to 255
Set Disable VSS to 256

[schpenxel]

Is access to those new? I don't recall ever seeing them before. Or maybe I just wasn't looking.

[dreksnot]

Is access to those new? I don't recall ever seeing them before. Or maybe I just wasn't looking.

Thanks, I'll try that on the way home from work tonight!

[dreksnot]

Engine
->Fuel
--->Open & Closed Loop
----->LTFT Idle Cells Thresholds

Set Enable VSS to 255
Set Disable VSS to 256

Worked like a charm. As usual, Dave knows what the hell he's talking about. Just have to tweak some VE numbers down low to smooth out the idle and coastdown areas on the chart then should be good to go. Thanks!!!

[schpenxel]

Awesome

[VodeAn]

Thanks for all the responses. I had the VVE low to try to compensate for the 29% fuel being added during decel. The problem isn't with DFCO, as the issue is present below my DFCO disable RPM. I'll give Dave's fix a shot.

[coolmo]

Helped my ZL1 also.
That going lean on decel makes it hard to tune on the street. Skews the data lean.
before vss.PNGafter vss.PNG

[veee8]

I have found on the newer stuff that if the rear o2's are not present or switching correctly, it will do this as well.