AFR While Off Throttle (Coast)

[tatasta]

1999 A4 Trans Am, stock bottom end, H/C/I w/TR224-112, 3400 stall

Currently running COS5 in OLMAF.

AFR is running very well in all areas except when I let off the throttle and the car is coasting.

The AFR goes right to ~12.5:1 when throttle is closed.

I attached my tune and a piece of log file for reference.

Thanks

[BRD-PREY]

No expert but did you look at:
DFCO deaccel fuel cut off?
To quote the book "Master EFI Tuner" by Dan Maslic
Deceleration Fuel Cut-Off, DFCO for short. This function is used primarily to aid in higher fuel economy and lower emissions.
Throttle Cracker
Throttle Follower
They work inconjuntion to reduce the impact of just instantly closing the throttle.
Transient Fuel Impact Factor
This adjustment is for how fuel reacts to its environment (during transient period) . It considers intake runner length, air temp, manifold fill times etc. and allows adjustment for fuel effects like boil time etc.. Best to leave alone without the right equipment and knowledge.
I hope this helped.
Ed

[redhardsupra]

what injectors do you have? most cases of rich-on-decel are a function of not having good characteristics for short pulse fueling.

[tatasta]

what injectors do you have? most cases of rich-on-decel are a function of not having good characteristics for short pulse fueling.


They are 33# @ 3 bar LS1 injectors. I have not changed any tables for them other than adjusting them for proper IFR.

Any thoughts on where to start on short pulsing adjustments.

Thanks

[hquick]

B3701 has a VERY big effect on off throttle fuelling.

[tatasta]

B3701 has a VERY big effect on off throttle fuelling.

Ok.

[LS1_Dragster]

And what would one do with that table to help with this problem?????

[hquick]

I played with this table a LONG time ago.
From memory...try lowering the numbers slightly in the 9.5-11.5 range and see if it helps. If you're hitting DFCO and it's not cutting fuel properly (ie...it's still kinda flicking on and off) then lowering the values slightly should help.
I found it made a big difference when I was going very rich on decel.

[tatasta]

I played with this table a LONG time ago.
From memory...try lowering the numbers slightly in the 9.5-11.5 range and see if it helps. If you're hitting DFCO and it's not cutting fuel properly (ie...it's still kinda flicking on and off) then lowering the values slightly should help.
I found it made a big difference when I was going very rich on decel.

I will take a look at it and report back once I get a chance to try it.

Thank you

[5.7ute]

what injectors do you have? most cases of rich-on-decel are a function of not having good characteristics for short pulse fueling.

X2
After doing a lot of work on injector characteristics I have found many reasons for the rich decel/idle problems that we face with larger injectors. Injector voltage offsets, small pulse adjust & default pulsewidth seem to be the main culprits.
look here http://forum.efilive.com/showthread.php?t=10179&highlight=IBPW
and here http://forum.efilive.com/showthread.php?t=10930&highlight=IBPW

[tatasta]

X2
After doing a lot of work on injector characteristics I have found many reasons for the rich decel/idle problems that we face with larger injectors. Injector voltage offsets, small pulse adjust & default pulsewidth seem to be the main culprits.
look here http://forum.efilive.com/showthread.php?t=10179&highlight=IBPW
and here http://forum.efilive.com/showthread.php?t=10930&highlight=IBPW

Thank you. I will take a look at them and see what I come up with.