I have a S4 TII engine without a turbo, controlled by an Adaptronic E420D ECU, 460CC N/A injectors.

I have overrun fuel cut disabled, and for some reason I get a lean spike of 16:1AFR and higher at 2200-2800RPM only, and only on overrun, free revving, and engine braking

I have tried adding more fuel, I am using VE tables, and going from 38% VE to 54% and it made a slight difference, my AFR dropped to 15.5 only. I have tried different timing, from 35BTDC to 12BTDC, with no difference. My AFR at 2800RPM and up and 2200RPM and below is 13.5. It just shoots up to 16 for those few hunderd RPM, then back down.

Since its only in overrun, light cruise and high load in that RPM range is fine, I am not too worried, I am just wondering if this is a normal trait or something bizzar.

 

Post your map.

 

I attached my latest map, and also screen shots of my fuel map up to 4400RPM as its all that will fit on my laptop, and also 2 ignition maps, the only difference is the overrun, I tried drastic different timing, with no change at all.

My overrun is a steady 30KPa, idle is at 51KPa, 950RPM.

 

Forgot to ask for a log as well.
My initial guess would be the Idle Control section as there are cuts and adjustments for throttle off.

 

Does yours do the same thing as well?

I'll add this graph from a log, showing my AFR averages with the same scaling as my map, its not showing as lean in the area, but there is a definite lean spot in that one area.

I'll also add one with my idle motor position, ignition timing, fuel injection pulse width, I checked everything in my logs, nothing goes out of place in this area other than the AFR.

I am using the stock S4 BAC, minimum duty is set to 60% as that is where it starts to alter the RPM, so 60% is closed.

My AFR's are a little rich, the engine seems to run the best there, especially at idle, never been able to get a steady idle above 12.5, it just hunts and stalls easily, above 11.7 it the idle gets harsher.

 

I do not have that problem.

Can you post the excel? From your RPM vs. Map vs. AFR map, its most predominate at 2100-2400 and 0kpa. That sounds like a tip-in situation to me, vs. what you stated.
The excel should provide a better understanding of the trend, since I don't have the car.

 

Oh, sorry, misread your post above.

Here is a log file of me driving home from work, if I have a chance, and remember, I will try to get something better.

I also attached my latest map.

 

I should also add that I have had a nasty misfire (I guess) only when over 70% is throttle, and only at 4500RPM (give or take 300RPM), but it is always at the same RPM, and only when accelerating hard. Normal driving, and under 50% throttle, not a hickup.

I used to have a misfire at 70MPH in top gear when going up a slight incline, but advancing the timing cleared that up, but I cant get rid of the 4500RPM misfire. Looking at every value on my log, nothing changes, nothing bounces, only the RPM can be seen jumping a couple hundred RPM for a second or 2 when I push past it, and it runs fine up to 7400RPM. To me it sounds like a soft ref limit by listening to the exhaust with the window down, no backfires or pops.

Not sure if that could be related.

I made a different thread on it, but it went cold. But in a nutshell, I added/removed fuel, no change, same with timing, changed plugs, wires, leading coil, no change.