AFR rising at deceleration , is it a problem?

[abumalik]

Hi,
after months of reading and learning and trialing I managed to get my tune to where I think it is 90% OK. Remaining bit is to play with spark table to get additional horses (expecting 50+ than what I am currently getting).

However, before proceeding I am bit bothered by noting that my WB AFR readings shoots up (goes Lean) when I decelerate. The car is manual transmition. I tried disabling the DFCO but didn't make any difference.

engine specs :
416 ci,
cam 236/242 , 0.6 lift and 112 lobe
Intake System: GM L76/LS3 intake, 39lb injectors, fuel rails, Fast 92mm throttle body.


attached log file , config file and last tune.

appreciate any insight on the issue or the tune in general if relevant.

[WS6FirebirdTA00]

DFCO is not fully disabled.

[69lt1bird]

You never changed your engine size in the engine/general section, it still thinks its a 5.7L.
Why the hacked up VE table?

I am guessing you have long tube headers, sometimes the lean decel is due to the location of the WB, it gets air pulled back up the exhaust during decel which shows up as lean on the WB.

[WS6FirebirdTA00]

Yeah that will mess you up too

First and only thing I looked at was DFCO.

[69lt1bird]

What else should he mess with for the DFCO?

[WS6FirebirdTA00]

The clutch transition could also change it. I didn't see the log, just checked to see if all DFCO was disabled. After that, I am sure there will still be the issue there based on your comments though.

[abumalik]

What else should he mess with for the DFCO?

indeed , what else I need to do apart from the ECT setting ?

[abumalik]

You never changed your engine size in the engine/general section, it still thinks its a 5.7L.
Why the hacked up VE table?

I am guessing you have long tube headers, sometimes the lean decel is due to the location of the WB, it gets air pulled back up the exhaust during decel which shows up as lean on the WB.

First thank you all for your replies.

Regarding engine size, I believe that is set via the cylinder volume field, what you are referring to is just a label (at least that what I thought as there is no option to select 416 ci or 6.85 ltrs).

My headers are fairly short actually , 20 inches or so. The WB is some 6" downstream from where the 2 banks merge. The WB trend is in agreement with the 2 NBs. Distance from WB sensor to the tail pipe (exhaust end) is more than 3m , so I don’t think it is sucking air from outside. And yes , I did check for leaks but non found.


What do you mean by "hacked up VE" , too high or too low ? . During acceleration (when the system switches from MAF to SD and uses the VE table), it runs at around 12 AFR which is where I want to be.


Any other thoughts !!

[abumalik]

The clutch transition could also change it. I didn't see the log, just checked to see if all DFCO was disabled. After that, I am sure there will still be the issue there based on your comments though.

Clutch ?!, OK , that I will try next. I don't have a VSS so I will use the ECT parameter again as a trigger.

From the replies so far , this seems to be a real issue and not a normal thing that I should live with. I already blown a piston during my "quest for knowledge" and now prefer to learn in a less costly manner.