Using 4D fuel table?

[banaro]

Hi,

Have a blown SBC that makes very little vacuum at idle (cam 280deg@50)
Long term a have been using an ECU the uses a single fuel table with a calibration method of TP / MAP, with the map x axis being TP, it seems that TP and rpm referenced tuned cell values are adjusted by the ecu for MAP automatically. This has been good to me so far.
 

What link ecu methods produce the same result?

Using load BAP/Map crossover, TP main axis X on fuel table 1, and enabling the 4D fuel  table and fill with 0s?, or maybe just leave the 4D table disabled?

Thanks for your help

[Adamw]

Set Equation load source to MAP, then put TP on your main fuel table axis.  If you are using traditional mode then make sure open loop lambda table is turned on and put MAP or MGP on its Y axis.  MAP will then be taken care of automatically in the background and the open loop lambda table will take care of the fact that you want a richer mixture at higher boost.   You will unlikely need a 4D table or BAP/MAP Xover mode.

[banaro]

Thanks Adam

Is it correct to assume that MGP is a calculated i/p, and is available as long as a MAP and BAP are present

Thanks

 

[mapper]

I don't agrre that you don't need a 4D table if you use TP vs RPM on the main table in a boosted application. 

I use this strategy on most tunes. Turn the boost down as much as possible, the. Tune the main table. Once main table is tuned turn up boost step by step and make all changes for higher boost in the 4D table. So the 4D table compensates the blower or turbo efficiency change with boost. 

4D table must be spanned MGP vs rpm or MAP vs rpm. 

[AbbeyMS]

3 hours ago, mapper said:

I don't agrre that you don't need a 4D table if you use TP vs RPM on the main table in a boosted application. 

I use this strategy on most tunes. Turn the boost down as much as possible, the. Tune the main table. Once main table is tuned turn up boost step by step and make all changes for higher boost in the 4D table. So the 4D table compensates the blower or turbo efficiency change with boost. 

4D table must be spanned MGP vs rpm or MAP vs rpm. 

Adam is correct , span your open loop AFR table correctly for the AFR's/Lambda you require , then tune the main map at base boost when raising the boost the AFR/Lambda will be automatically tuned. Works real well. Motec  works the same as well. Also allows quick changing in fuelling to see if a car likes a leaner/richer mixture , no need to change the whole fuel map just tweak the AFR/Lambda table and run a pull on the dyno

[banaro]

That helped thanks, I had not thought much about the AFR/Lambda tables influence.

[mapper]

I just read the initial question again. 

Sorry my answer hasn't covered the initial question right. Think all answers are right in this thread. Because, yes the VE Fuel modell takes MAP, Target AFR and Target AFR into the calculation. 

The VE modell makes the assumtion that the volumetric efficiency stays the same on all boost levels. In reallity this holds not true. If you make big boost changes you want a 4D compensation to correct for VE variation with higher boost levels. This is needed, because the pressure ratio of the turbo or supercharger with boost. Consequently the turbine efficiency and with this the VE of the engine changes. Other mechanical parts like small, intake, exhaust can restrict VE at higher boost levels too. 

Usually tuning ends up with only small percent numbers on thr 4D table. If the engine flows well it's usually a good reflection of the turbo charge efficiency map. When you start with Wastgate boost (as low as possible) and turn boost up step by step you usually have to increase fuel by a few percent when the turbo is operated in it's sweet spot (max efficiency  on turbine Flow chart). Once you passed the max turbine efficiency range (you are now on the right side of the turbine efficiency Map) 4D fuel must be reduced. 

[banaro]

Thanks mapper, VE must vary somewhat for different boost levels, so the calculation cannot be quite right, be a bigger issue for a turbo setup, being a belt driven charger, normally I would fine tune this combo with its normal boost levels present, so less risk of what you say occurring, but it does make we wonder about combo VE, and because i am bringing this combo over to a link ecu and have no starting map, I am wondering whether it would be smarter to perform a base tune without the charger installed first, on fuel table 1, if i did this the 4D method could tell me a lot about the efficiency of the combo?

[Dave Kriedeman]

Hi,

depending on setups i use either dual fuel table or 4 D fuel table.

All comes back to the mechanical differences and VE of the engine along with many other variables.

Next time you have this tuning hurdle try the dual fuel table option versus the 4D and look at the differences especially around 100 KPa or 0 MGP change over areas and the effects on the fuel table values and or the effects on the tune as the engine goes on boost.

Food for thought.

Regards

Dave.

[Purpleline]

Wonder if i can use a 4D table to reduce fuel during 0% throttle.  Im asking this bcoz everytime i left my foot off,  AFR will jump to something around 12 before the overrun fuel cut kicks in.  As i recall,  the stock ecu will lean out right away i left off.  

[cj]

Sounds like you just need to drop the activation delay for fuel cutoff

you can also just set the *very* low values of your fuel table to be really low numbers - Assuming a MAP based table, the 10-20kpa lines at >3k rpm are probably only ever hit on overrun.

[Purpleline]

Yes,  i have both u addressed set like 0.6 delay and the fuel area at a lower numbers.  The zero throttle situation can hit any large fuel no bcoz there is need for overrun delay.  So the gap is always there.  Thats why im curious if i can crossover a 4D table which is TP load to correct MAP based cant do. 

[Adamw]

You can add a 4D table if you like with TPS delta on one axis to remove fuel only when throttle is quickly closed,  but even with no fuel going in at all you will still have the initial fuel evaporating of the port walls which will give a rich spike.

Why are you concerned about AFR when the throttle is closed?

[Purpleline]

I know it might be a strange question.  In my point of view,  if there is a function that i could optimize and not going to hurt or even it will be a good thing in long runs.  Why not use it. Even a little of saving and ECO,  it is good.  And i really want it act as stock designed possible on this.  We here on and off all the time bcoz of traffic.  This might be a noticeable different amd i can avoid any possible of exhaust poping and less carbon build up in the cat.

Tks mate.  Will give it a try and see if it will make diff on the spike

[cj]

How about testing the "extreme" option first to see if there is actually anything to be gained from your time & effort. As Adam said, the whole fuel wetting thing will likely prevent you getting this perfect, but if you just set overrun cut timer to 0, and accept the problems from this for a day or so, you will see in your logs whether this problem is actually fixable with your engine. If this test behaves excatly as you expect, or you at least see a lot smaller rich spike then there is likely a combination of settings to behave the way you want and still perform well. If this test still shows a very similar rich spike, then you know that no amount of shortening the timers before cut or using tables to do the same thing will actually help.

On a more theoretical note, all modern OEM emmissions strategies oscillate a bit rich & lean regularly because it has some sort of emmisions benefit vs holding exactly lambda1.0 all the time. Because of this, short rich spikes in your tune are probably "good" for your cat if there are similar lean spikes a certain loads, or at least the will benefit the emissions purposes that it's there for.

[Purpleline]

Great points. Thank you for your input. 0 delay may happen problem during shifting but would see which way make the different and what will work or none.   

[Purpleline]

I have 2000 to 5000rpm -5%.  Looks like it does make some different.  Spike still there as expected but much short