E40 lean on decel even without DFCO

[[email protected]]

I have a swapped colorado running an e40 ecm. I swapped the 5.3 for a 6.0 and I'm having trouble with tuning the maf due to a lean decel issue. I have DCFO and CFCO both disabled and this happens in MAF only as well as VE only tuning. The issue is present when revving in neutral (as in the log) as well as when letting off throttle in gear. the log and tune below are with maf only. I have swapped to a lot of new parts along with the 6.0 and I'll list them below:

OLD // NEW
24.8lb injectors // 36 lb injectors (12613411)
gen 3 style truck intake // tbss intake (and MAP sensor)

other specs:
LS2 with 228/230 .585/.585 112LSA
gapped rings for future boost (currently NA)
stock 243 heads

I've searched through the forums quite a bit and have found similar problems but without solutions that fix my issue. I've got a feeling it has something to do with either my injector settings or my transient fuel. I should also point out that on my old setup my maf hz would drop to ~2800 on decel but now they only drop to 3500-4000 which is referenced elsewhere in the tune. you can see radically different afrs at that same point in the maf curve in the below file. I never used to have this issue with the 5.3 setup. I'm still learning tuning so I really appreciate the help you all have to offer. Please let me know if you'd like me to include more information/PIDs.

fuel cutoff on decel.hplve step10 + maf o2 EMERGENCY MAF ONLY smoothed ve.hpt

[hjtrbo]

I had a similar issue with my mystery injectors installed that were still using the same factory data except the flow rate which was scaled to suit the injectors. I would be +25% lean on decel before DFCO kicked in etc. To fix this I worked with the Flow Offset vs MAP table. I normally idle at 55-60kPa so the cells below this I reduced the numbers which lowered the flow rate for the high vacuum areas (25-45kPa).

[[email protected]]

I had a similar issue with my mystery injectors installed that were still using the same factory data except the flow rate which was scaled to suit the injectors. I would be +25% lean on decel before DFCO kicked in etc. To fix this I worked with the Flow Offset vs MAP table. I normally idle at 55-60kPa so the cells below this I reduced the numbers which lowered the flow rate for the high vacuum areas (25-45kPa).

thank you so much! i adjusted the map up from the old injectors but ill mess with it a bit more. ill post an update tomorrow.

[[email protected]]

i changed the flow rate from <30kpa all the way down to 20lb/hr for testing and the issue still persists.
20lb at low vac log.hpl
20lb at low vac tune.hpt

[[email protected]]

i changed the flow rate from <30kpa all the way down to 20lb/hr for testing and the issue still persists.
20lb at low vac log.hpl
20lb at low vac tune.hpt

update for anyone who finds this thread

i did not end up getting the lean off throttle issue figured out BUT i did figure out how to tune the MAF around it. in the scanner i added a filter to my AFR error/MAF freq. table to only add values when the map sensor is above 30kpa. this gets rid of most if not all of the off throttle lean spikes in my data and allowed me to tune the rest of the maf curve within 1%.