2017 L86 rich on deceleration

[Dominatorstang]

Is it normal to see a rich mixture trying to happen on decel for a E92A ECM? At first I thought it was my VVE or MAF, but honestly it does it no matter the values. But the STFT tries to pull the fuel back out. usually 15% rich or so. I try to filter it out in my logs, but curious if this is just a normal thing for these models and if I can disable that somehow? I will get a log and tune posted up shortly to better explain too.

I could understand one bank rich if I had an injector leaking, or both banks lean from a vacuum leak. I also have gotten a chirp sound on light load around 1200RPM which I am guessing is a tiny exhaust leak, but I have been unable to find it.

[Dominatorstang]

This is a log from from an OL run down the highway with MAF failed. I have DFCO disabled and forced OL in the scanner.

vve2.hpt
VVE tuning OL highway.hpl

[Dominatorstang]

Trying to upload a log from closed loop but it was just under 10MB and keeps not uploading. Maybe file size limit? Anway, I notice this run also has DFCO enable RPM set to disable. I will try putting DFCO back to stock tomorrow and see how a log looks. Maybe it is just that its not fully disabled and doing some strange things.

[Dominatorstang]

Well it appears trying to shut off DFCO on decel caused these odd rich mixtures. I have went back to just using stock DFCO settings and I find it much easier to filter out with DFCO actually happening than it was with this odd rich mixture.

[Dominatorstang]

So I am still stuck on this... DFCO enabled or disabled then my STFT's start chasing a rich condition on decel or very light throttle like 1-3% throttle. First I thought maybe this was my HPFP misting into the lifter valley and the PCV sucking it into the engine which sounds possible especially since I ran across a GM TSB for it happening. I tried a spare HPFP and noticed no difference though.

Shane Hewitt gave me a tip on the EVAP maybe causing me some issue with idle FT's and such. I now notice my EVAP is certainly changing my FT's and I had pretty well dialed in my air with EVAP hooked up normal and the tune was acting really nice. I just wanted to fine tune some places that the rich decel was messing with me on.

So now I unhook the EVAP connector and hose. Then plug the port on the EVAP. This jacked my current tune up for fuel trims and virtual torque at idle. Made my cruising FT's add ~15% fuel too. The ECM is commanding the EVAP to be open most all the time so I can not see how replacing the EVAP would change anything and I know many folks just plug it which I have thought about, but I am not sure if this is normal.

Now the kicker. This did not help my rich decel very much if at all... So if I plug the EVAP then I have to retune airflow values and tweak idle torque tables, but not sure if plugging the EVAP really gains me much to where I should do that. I would think the ECM could better deal with the EVAP fuel vapors coming in to where it does not change FT's that far though

drive around town VVE.hpl
VVE log with evap plugged.hpl

[Dominatorstang]

Here was the current tune for those two logs.
with DFCO disabled best I can.hpt

[Haans249]

I have a similar issue when coasting after getting up to speed (say 50-60mph), if I let out of the throttle (just normal driving), my STFT shoot straight up to 32% causing excessively rich fueling (in the .75 to .85) if DFCO does not kick on. My guess is there is some relationship in the calibration that sends the STFT to the max expecting DFCO to cut off the injectors, so that when you start giving it throttle, or (in my case) the TCC unlocks to return to motor to idle, that there will be a quick return to fueling to prevent bogging or stalling. Totally a guess and not really sure what the solution is here. My MAF and VVE table are dialed in and it is only a condition of the no throttle while at speed.

[Dominatorstang]

That sounds like a good guess to me too.

TriPinTaz mentioned the below which sounds related too, and may be the best option at this time. I just keep hoping someone mentions that they figured out a way to eliminate it completely.

You can actually make DFCO kick in faster to negate that issue. I have to do that on some cars I tune. Its a very vague setting and I don't know why it has the affect it does, but it does.

FUEL > OXYGEN SENSORS > LTFT IDLE CELLS THRESHOLDS > Change the Enable VSS and Disable VSS to speeds the car will never see. This will cause DFCO entry much quicker.

[Haans249]

That sounds like a good guess to me too.

TriPinTaz mentioned the below which sounds related too, and may be the best option at this time. I just keep hoping someone mentions that they figured out a way to eliminate it completely.

Does this setting affect STFT? Cause I have my LTFTs disabled.

[Dominatorstang]

I am not sure. I tried it and did not have much different results but I was fighting other issues too so it was not a clean test. I plan to try it again soon. I too currently have LTFT disabled.

[Haans249]

Intried those settings and it has made the rich condition better by entering DFCO more often, but it had no effect on my STFT’s spiking to +32%.

[humandm]

I had this same problem on a C7 A8. Fix was to set Enable VSS to 255 and Disable VSS to 256 under Fuel, Oxygen Sensors, LTFT Idle Cells Thresholds. This fixed both the richness when DFCO was not active and allowed predictable DFCO engagement which is controlled by the other parameters.

[Haans249]

I had this same problem on a C7 A8. Fix was to set Enable VSS to 255 and Disable VSS to 256 under Fuel, Oxygen Sensors, LTFT Idle Cells Thresholds. This fixed both the richness when DFCO was not active and allowed predictable DFCO engagement which is controlled by the other parameters.

I’d describe it as more of a bandaid than a fix. We definitely are missing some tables.

[32vape]

After a reflash, the ecm will go through some self tests to validate o2 sensor switching and catalyst efficiency. Part of the emissions monitor tests. If certain codes are shut off the ecm can never complete the tests and it will continue to add the fuel after a decel. Shutting off the ltft idle cells is the only way we can eliminate it with this software. I think there's going to be a lot more people learning winols in the near future.

[Dominatorstang]

That would make sense to me too. Thanks for the tips!