RomRaider

Deceleration - Fuel Enleanment

When reducing throttle, the decrease in manifold pressure causes fuel that has condensed on the walls of the intake manifold to evaporate and be ingested by the engine. This can result in a temporary rich trend in AFR and to counteract that, the ECU will reduce injector pulsewidth temporarily and then gradually return to steady state fueling. This function is similar to 'Acceleration - Fuel Enrichment' but is used during decelerations instead.

There are two scenarios that apply; First Triggering (FT) and New Triggering (NT).
- FT occurs when the ECU has not run this function in a 'while'.
- NT occurs when there was a recent FT event and another Negative Throttle situation was calculated shortly afterwards.


Fuel Enleanment - Negative Throttle - Initial
During a FT event, this table is multiplied to the 'Fuel Enleanment - Negative Throttle - Nominal' table to determine Fuel Enleanment during Negative Throttle. However, during a NT event, the value used during the last FT event is multiplied to the 'Fuel Enleanment - Negative Throttle - Nominal' table which is then multiplied to the 'Fuel Enleanment - Deactivation Factor' table.

Fuel Enleanment - Negative Throttle - Nominal
This table is used during both FT and NT events.

Fuel Enleanment - Negative Throttle - Session Duration
This table is used during a FT event and determines the duration of each 'Fuel Enleanment - Negative Throttle' session. The value decrements every ECU cycle and after it reaches 0, if Negative Throttle occurs again, it will be considered a FT event.

Fuel Enleanment - Deactivation Factor
This table is used to slowly decay the applied 'Fuel Enleanment - Negative Throttle' and takes place over the duration set by the 'Duration' table.

Deceleration - Ignition Retard

These tables are used in collaboration with the 'Deceleration - Fuel Enleanment' tables to retard ignition timing and prevent engine acceleration when shifting. This condition may also be referenced as 'rev hang' and can be tuned to the driver's preference. Some prefer the Engine Speed to come down quickly to enable fast shifts while others may prefer a more gradual engine deceleration.


Ignition Retard - Negative Throttle
Ignition Timing is gradually reduced by this table when throttle is slowly reduced but not closed.

Ignition Retard - Slow Negative Throttle (Closed)
Ignition Timing is gradually reduced by this table when the throttle is slowly reduced and closed and AC is off. Once the full amount of Ignition Retard is applied the fuel injectors may be shut off depending if Engine Speed is above another threshold or not.

Ignition Retard - Slow Negative Throttle (Closed) (AC on)
Ignition Timing is gradually reduced by this table when the throttle is slowly reduced and closed and AC is on. Once the full amount of Ignition Retard is applied the fuel injectors may be shut off depending if Engine Speed is above another threshold or not.

Ignition Retard - Change Limitation A
"Ignition Retard - Change Limitation A" and "Ignition Retard - Change Limitation B" are added together to calculate a 'step size' which is used to determine how gradually Ignition Timing is allowed to decrease when throttle is slowly reduced. This is used during both "Ignition Retard - Negative Throttle" and "Ignition Retard - Slow Negative Throttle (Closed)" but not "Ignition Retard - Fast Negative Throttle (Closed)". A larger 'step size' will result in a faster change to applied Ignition Timing.

Ignition Retard - Change Limitation B
"Ignition Retard - Change Limitation A" and "Ignition Retard - Change Limitation B" are added together to calculate a 'step size' which is used to determine how gradually Ignition Timing is allowed to decrease when throttle is slowly reduced. This is used during both "Ignition Retard - Negative Throttle" and "Ignition Retard - Slow Negative Throttle (Closed)" but not "Ignition Retard - Fast Negative Throttle (Closed)". A larger 'step size' will result in a faster change to applied Ignition Timing.

Ignition Retard - Fast Negative Throttle (Closed)
Ignition Timing is immediately reduced by this table without any gradual steps when throttle is quickly closed and the fuel injectors are shut off. This table does not get used if Fast Negative Throttle Detection is disabled.

Deceleration - Fuel Cut


Fuel Restore - Engine Speed
Below this Engine Speed, fuel injectors are always on. To disable fuel cut during deceleration with the throttle closed, increase this table as high as you want.

Fuel Restore - Engine Speed (AC on)
Below this Engine Speed, fuel injectors are always on. To disable fuel cut during deceleration with the throttle closed, increase this table as high as you want. This table is used when the Air Conditioning Compressor is on.

Fuel Cut - Engine Speed Hysteresis (Maximum)
If Engine Speed is above the sum of this table plus one of the Fuel Restore tables, fuel injectors are cut if the throttle is closed. Whether they are cut immediately or after Ignition Timing is slowly retarded depends on if Fast Negative Throttle is detected. Additionally, Engine Speed must be greater than the "Intercept" threshold and the Derivative component of Idle Speed Regulation must be 0 for fuel injectors to be shut off. This table is used while the "Delay Counter" is not 0. This is to prevent the fuel injectors from turning on and off continuously.

Fuel Cut - Engine Speed Hysteresis (Minimum)
If Engine Speed is above the sum of this table plus one of the Fuel Restore tables, fuel injectors are cut if the throttle is closed. Whether they are cut immediately or after Ignition Timing is slowly retarded depends on if Fast Negative Throttle is detected. Additionally, Engine Speed must be greater than the "Intercept" threshold and the Derivative component of Idle Speed Regulation must be 0 for fuel injectors to be shut off. This table is used once the "Delay Counter" has decremented to 0. This is to prevent the fuel injectors from turning on and off continuously.

Fuel Cut - Delay Counter (Hysteresis Selection)
This table is initialized when fuel injectors are shut off and decremented every engine revolution when not in 'fuel cut' mode. When this value has reached 0, the "Engine Speed Hysteresis (Minimum)" table is used otherwise the "Engine Speed Hysteresis (Maximum)" is used. This is to prevent the fuel injectors from turning on and off continuously.

Fuel Cut - Engine Speed Hysteresis (below Coolant Temperature @ Engine Start)
This table is used instead of "Fuel Cut - Engine Speed Hysteresis (Maximum)" if Coolant Temperature at Engine Start is less than "Fuel Cut - Coolant Temperature Threshold".

Fuel Cut Hysteresis - Delay Counter (below Coolant Temperature @ Engine Start)
This table is used instead of "Fuel Cut - Delay Counter (Hysteresis Selection)" if Coolant Temperature at Engine Start is less than "Fuel Cut - Coolant Temperature Threshold".

Fuel Cut - Coolant Temperature Threshold
If Coolant Temperature at Engine Start is less than this value, the "(below Coolant Temperature @ Engine Start)" tables are used.



The idea is to achieve this sort of exhaust crackle when off throttle.
https://www.youtube.com/watch?v=UWhZcsbNASs

Just listen to that deceleration noise!
https://www.youtube.com/watch?v=I6KFA7p7_aQ

anyone do that in their tune?

I have on mine and some customer's Subarus. I'd like to do the same on my M3.

Hmm. My 328is with S52 cams, M50 manifold, and tune crackles like that all the time. My S52 M Coupe, and other M3's, I've never heard do so.

I'll have to drop the muffler off (M3 muffler quiets it too much) and take a video. It crackles and sounds great. The tune didn't have any of those edited.

Yes, please do!

Also, these tables are used in conjunction with the Acceleration/Deceleration Detection tables. If you disable Fast Negative Deceleration, you'll keep the fuel injectors on for a while. Otherwise, they'll shut off.

The Acceleration/Deceleration Detection tables determine whether the Positive, Negative, or Fast Negative Throttle tables are used.
viewtopic.php?f=42&t=11392

To get exhaust crackes, we need to keep the fuel on and retard ignition timing. So disable "Fast Negative Throttle" detection and use the "Ignition Retard - Slow Negative Throttle (Closed)" to retard timing as necessary.

328 has other maps as M3 US.
Here's an example of my 328 vs M3 us.
Ihnition retard negative throttle.Left M3 US right my stock 328bin.


My 328 shoots a little in the exhaust

Keep in mind that when comparing tunes, all maps in a particular group should be compared together to get an accurate understanding of differences.

Yes. You're right.Just gave the example.I have not looked through all,but in all there are differences.
Soft M3 US is, in many places, "ecological" .Probably due to the lambdas after CAT.
Effects on shots from the exhaust will have COP enrichment.
I removed the COP enrichment from my ecu.Almost no exhaust crackes.
Decreasing and enrichment overlap.

Here's the promised video:

https://onedrive.live.com/?cid=b62fe934 ... gw3Vo_wyw0

Probably best if you play it with headphones, but it's good I think. I don't have a GoPro to film outside.



Here are the locations of all the Deceleration Maps in MS41.1 ID60:

I do hear the exhaust crackle but it's not consistent. Are you lightly on throttle during the times we can hear it? Maybe just enough to get the ECU to think it's not fully closed?

I've noticed it does it mostly on deceleration at 3000 rpm and under. I am completely off the throttle when it does crackle/burble, but it's one set of crackles at a time, until repeating an acceleration and then deceleration again. It very very rarely burbles the whole deceleration down. It used to do it more often, but it's been a while, and many maintenances/different flash now.

If I can find the fast negative detection on ms41.1 I'll play around with it tomorrow.

You said to disable fast negative detection. Would that be all of the fast negative values? I think there was rpm, vs, etc

There are many thresholds that all have to be met before FNT is allowed to be active. So you can disable any one of them and the entire FNT logic will be ignored. Only caveat being the Min. RPM and Min. RPM Gradient thresholds which work in a pair and they both have to be disabled together because either one of them if met will allow FNT. The most appropriate thing to disable would be the Min. Throttle Gradient threshold by setting it to max negative. Keep in mind, this will not keep the injectors on forever during decel. It will just force the SNT Ignition Retard maps to be used which gradually lower applied Ignition Timing. Once Ignition Timing retards as much as those maps allow, fuel will be cut. So what you should get is a burble for a while then fuel cut. But, this will only happen over a certain RPM threshold because below that you'll experience what Enabled posted about regardless. Also, look at the SNT maps they have 0 retard at 5000 RPM gradually increasing to -15 at 2700 RPM. So I would change the SNT Ign. Retard maps from "-23.25 -25.50 -15.00 0.00" to "-23.25 -25.50 -30.00 -30.00"





Thanks for the input.