How much the A/F should be when releasing throttle after hard acceleration?

[wesam]

How much the A/F should be when releasing throttle after hard acceleration?
I mean in Manual transmission cars between shifts the MAP goes to 15-25 kpa
so in this area how much the A/F ratio should be ?

[WeathermanShawn]

Mine spikes to 20.0 AFR..DFCO..:grin:..http://forum.efilive.com/search.php?searchid=941785

[wesam]

so my car should be recalibrate because I'm seeing 12
but i want to know what is the ideal A/F for this area

[WeathermanShawn]

Are you saying during shift (clutch-depressed) or after clutch released, but no throttle.

Neither needs to be tuned. DFCO turns off injectors on M6 during shift..http://forum.efilive.com/search.php?searchid=941790.

If you get a richer AFR after shift, but foot off throttle..thats momentary. Called rich decel..http://forum.efilive.com/search.php?searchid=941792..

DFCO you can turn on and off (see links). The other would have to be tuned via transient parameters. (see links)..:)

EDIT: Stoich would be ideal..but there is so little cylinder air, it is virtually impossible to decrease the injector pulse width below its minimum. Thats why most tuners don't chase it. But, if you are really curious 5.7ute has novel ways of tuning that area.

[wesam]

I meant when clutch-depressed and no throttle what is the ideal A/F ?

[WeathermanShawn]

While technically 'stoich' is ideal..since there is no load on the engine, and very little cylinder air..no fuel is required.

I say on a M6 enable DFCO B3308. It momentarily cuts off the injectors..

I do not believe there is any other way to manipulate fueling during a M6 shift other than B3308..

[wesam]

i look in my tune it seems that the DFCO is not active since the B3308 DFCO enable temperature is 140C
i will try to enable it will i need to tune any thing else after decreasing the temperature ?
will the car go very lean ? its running in open loop sd

[WeathermanShawn]

Its totally known as 'tuners option'. A lot of tuners when utilizing AUTOVE for SD Tuning, disable DFCO. That is to not have the brief interruption of the fuel injectors effect the RPM/MAP wideband readings while tuning AFR.

A number of tuners after completing AUTOVE leave DFCO disabled. Probably an equal number of tuners re-enable DFCO. Its true you go 'lean' for a moment. Its also considered no-load on the engine..a total waste of fuel to spray 1/2 second of fuel while shifting..and the engine does not need it.

The bottom line is its your option. Personally on my application, I leave DFCO enabled, including during shifts (M6 DFCO Temp: 50C). As soon as you hit the throttle Commanded AFR only takes 1/16 of a second to re-engage. If you stay rich during throttle shift, most likely you hear a quick 'pop' as any unburnt fuel during shift blows out the exhaust pipe.

The bottom line is that I have not heard of anyone who can alter the AFR during a M6 shift via any tuning method other than DFCO. I would just do a search on it and make up your own mind. If you are in the active process of AUTOVE..leave it disabled..

Good luck with your search..

[wesam]

Shawn i'm glad for you for that explanation
and thanks a lot for told me to leave it deactivated while i'm in the AutoVe tuning

[wesam]

so is it useful to try to lean those spots after making a log for the car ?

[WeathermanShawn]

Again, optional. Here is a screen-shot of a 2-3rd gear shift on a highway on-ramp. I 'short-shifted' (less than max rpm). You can see the momentarily spike in both Commanded AFR and actual. (about frame 92). Also, look how quickly it goes back to Commanded.

Total opinion..I prefer 'lean' during shift. There is a phenomena called 'rich misfire'..if you throw too much fuel on the engine with no load..it will hiccup.

DFCO may prevent it. I would not 'tune' around it. When you are through with AUTOVE try a few runs enabled..you can judge then.

EDIT: Attachment 1 is right on DFCO Shift (frame 92)..

[mr.prick]

Ahhh the ol' off throttle rich spikes. :hihi:
I don't think this can be eliminated.

Try logging NBO2 voltage and IBPW.
You might see that those two will differ from WBO2.
I think its from the exhaust pressure dropping so quickly. :secret:

If you ease out of the throttle AFR will ramp out inline with commanded AFR.
I'd like to see a not filtered log of someone who does not have this when slamming the throttle shut out of PE.

[WeathermanShawn]

I concur..

Unfiltered AFR coming off PE..I always go rich. (stock injectors). I just try to get DFCO to enable ASAP!:grin:

[mr.prick]

Shawn, where is your WBO2 mounted?

[WeathermanShawn]

Passenger side..Right after the header collector..and before the cat.

I have it 'bunged' in about ~3 o'clock high..about 4-6 inches before the 'High-flow' cat..close to the narrowbands..:)

[dfe1]

One problem a lot of tuners have is letting AFR stay extremely rich during closed throttle operation. Others completely ignore this part of the fuel curve. Either way, if you're dumping fuel while the throttle is closed, you stand a good chance of cooking the catalytic converters. If a vehicle isn't equipped with converters, you're just wasting fuel. As for a rich spike on a rapid transition to closed throttle, I just looked at a log from my last dyno session and both the wide band and narrow band sensor readings drop immediately after the throttle is closed. That may be because my DFCO ramp settings are fairly aggressive.

[mr.prick]

I don't have DFCO enabled.
DFCO makes gear shifts a little too rough for me.

I don't believe AFR stays so rich off throttle, IBPW & NBO2 mV drop right away.
For me, the slower delta MAP/Load changes the less likely I will not see this.

[WeathermanShawn]

Mr. prick:

Are you saying the rich AFR is a 'false rich'. I.E. sensor reading vs actual?

I was just looking at my little Rich Decel..IBPW1 drops to .427 ms..essentially entering DFCO.

I have not found a good way to get that IBPW1 any lower..I could put it to near zero airmass and it still stays rich. I use DFCO more as a personal preference. Lots of hills etc..Fun to decel with no brake application.:grin:

[5.7ute]

wesam, what you are decribing is a transient condition in a low map area. As the others have said DFCO is the easiest way to stop this rich condition atm. Once we manage to do some work in the transient fuelling area this will change. But there is still a lot we dont know on how these tables interact.
The low map areas for commanded fuel, VE & timing should be tuned for when these areas are hit under normal driving conditions, not decel. That is why we filter throttle position when doing AutoVE.
Being a low load area you could command anywhere up to 17:1 AFR with some safety. Personally I leave it at stoich, but I never hit those areas anyway unless under decel.

[swingtan]

Just a note....

Rich spikes on throttle close will not be particularly effected by DFCO. My thoughts on it are....

The majority od rich spikes on throttle close are as a result of a combination of factors. These include....


PE Ramp Out time:


Ramping out of PE faster helps reduce the rich spike. This is pretty straight forward thinking, but gets missed at times. The faster the "commanded" fule comes back to where it should be, the faster the mixter leans out.

Residual Fuel Load AKA Dynamics:


This is the fuel left in the intakes and is known as "Wall Wetting". Under full load the PCM will be dumping a huge load of fuel into the manifold and not all of it goes into the cylinder before the valve shuts. The fuel that remains behind is added to the next cycle. If you close the throttle before the next cycle, there is a ton of fuel in there that isn't needed, so you get a rich spike till the mixtures "normalise" again.

You can mess with the dynamics to help with this, but it's a very tricky area to play in. I've been playing for a while in the E38 and still need to do more work. Playing with evaporation times may help, but I haven't tested that.....

Injector Timing:


This really goes along with dynamics, as altering the injection timing influences evaporation times. Firing injectors earlier means the fuel has more time to evaporate, so more is available for the next induction stroke. It also results in a more "stable" dynamics environment, though not as "stable" as firing the injectors really late.....

MAP Pressure:


Again, this is "dynamics" related. Some might remember basic physics, where a liquid will evaporate faster in a vacuum, than when it's under pressure. At WOT, the manifold basically see's atmospheric pressure ( or higher if FI ), but at throttle close, it will see a very low pressure. As the pressure drops, fuel evaporation increases, allowing more fuel to be available for the induction cycle. You can't do a lot about MAP pressure, but as you might have guessed, dynamics may help.



So over all, it's possible to tune out the PE-throttle close rich spike, but is it "really" needed? Personally, I like the idea of a sort "rich" spike on gear change to help cool things down a tad. It might not make a big difference, but it makes me feel like I'm doing something ;). It also helps reduce any tendency to "lean spike" on the following throttle open, again, it's not going to do a lot, but I'd rather be rich than lean....

Providing the rich spike was not excessive, say richer than 12:1, then I wouldn't worry too much.

Simon.

[5.7ute]

Great post as usual Simon.:cheers:
One thing to note is that the decay out of PE will be obvious by logging the commanded AFR pid. Logging the transient fuelling addition/subtraction is much more tricky.

[swingtan]

Exactly right. Working on dynamics is a black art ATM as you need to "guess" what the fuel is doing as the throttle closes. I have proven the PE ramp out rate though, and speeding it up does reduce the rich spike.

Another point to note for those with a manual, is the DFCO is not enabled when the clutch is pressed. The E38 does have CFCO though and should be disabled if you care about performance.

Simon

[WeathermanShawn]

Wow, that was one of the most enlightened posts I have read in a while. I bookmarked it for future reference.

That was really eye-opening about MAP and Fuel Dynamics..I literally never thought about evaporation vs pressure (vacuum) as it relates to fueling and throttle letup and WOT.

All of of sudden I 'got' it.
Thanks..great post!:cheers:

[swingtan]

Yes, it was a pretty loud "penny drop" when I was thinking about evaporation. The E38 has double the number of tables for dynamics, so it's a lot of interaction to work out :P

Simon.