AEM info Boost comp/cell by cell/ hybrid

[rpslaughter1982]

Just as part of my single build I have been doing some research into my AEM ecu. This is mainly due to bad experiences with 'tuners' mapping and I think it is much better that I have a vague idea of what is going on. I am really putting this info up to see if I'm on the right track. I am not a mapper and don't really intend to be, i just want to know what I'm looking at!

*The maps posted are examples and should not be used in cars. I have made up most of the values.*

 

I found the AEM site quite hard to find the relevant info and they are generally unhelpful to new users. Due to this the following are links that I found very helpful and may help others on this forum:

http://forum.aempower.com/forum/index.php/topic,11494.0.html

http://forum.aempower.com/forum/index.php/topic,6378.0.html

http://forum.aempower.com/forum/index.php/topic,9998.0.html

http://forum.aempower.com/forum/index.php/topic,17435.0.html

 

obviously the manual was read a view thousand times.

 

There seems to be 3 main ways to map the AEM: Boost compensation, cell by cell tuning and hybrid maps (boost comp in boost areas and cell by cell in vacuum.

 

I have made 3 maps up based on these techniques and hopefully they accurately represent each one.

 

I'm going to update and add to this thread later, I've got to go to the parents for dinner. More to come ...........

hybridexe311207.V1.19.zip

fullboostcomp010108.V1.19.zip

cellbycell.V1.19.zip

[Wez]

[Ryan.G]

I always Map Cell by Cell.

 

p.s good job on setting the fuel cut on those maps above at -14 psi to stop anyone using them

[rpslaughter1982]

Right then, there are many ways to get the same result on the AEM. What follows is my understanding of the 3 main ones. Most of this information was taken from the AEM site and any credit should go to them. It is also worth reading the links as they go into more detail than I have.

 

Cell by Cell:

 

You can create a fuel map using the traditional approach of tuning each cell to a specific AFR. As you can see in the cell by cell map this creates a graph that raises with load and rpm.

Here the tuner gets a value for each cell and this will give a set AFR for that cell.

There are a number of fuel trims for cold starting, possibly idle control, air temp etc but during normal running conditions it should work pretty much as the fuel map is.

 

Boost Compensation:

This works on the principle that if at a set rpm and X load, the car needs Y amount of fuel to get a certain afr. At the same rpm but at 2X load, the car will need 2Y to get the same afr.

The AEM has a boost compensation table that adds or subtracts a % of fuel from the fuel map based on load points. This can be viewed as a graph and typically if there is 0 fuel correction at 0 kpa, then at 100kpa you will get 100% added and at -100kpa , 100% will be subtracted. This correction will go right up to your maximum load point.

You tune the fuel map by doing a wide open throttle pull at the lowest load you can do and tune that load row to a set afr (lets say 11.5:1).

Once you have these values you can paste them to the whole map. Now the map will look 2D as you can see from the attached map.

As you tuned the map to 11.5:1, the car will run at that afr all the time, not good really. There are a number of ways that this is fixed.

 

One way is to tune a throttle correction table. This table found in fuel trims adds or subtracts a percentage of fuel based on throttle position. In the above scenario it could be subtracting fuel at 0 throttle position to change the idle afr. Cruising conditions can also be leaned out by subtracting fuel at throttle positions below 50-60%. The thing I don’t like about this method that you can go up the rev range at part throttle and be leaning out your afrs. Going up hill you may get into a situation where your load goes up and a small turbo might start producing boost, once again this table may lean out your fuel.

 

Another way is to modify the boost correction table. Taking the afr you want and dividing it by the afr you have will give you a % difference (i.e 14 / 11.5 = 1.21 means that if you add 21% to the 11.5 you get 14). You can apply this % to the relevant load point in the boost correction table and you should get your desired afr. In the above situation you may – 21% on top of the negative value you already have in the boost correct table to give you something around

-70% at 50 kpa for an idle of 14:1 afr.

 

You can also change the fuel map itself in the areas you want a different afr. By doing this your fuel map graph will not look 2D any more and may start to look more like a cell by cell map (although not as steep). The benefit of doing it this way however is that you gain resolution in the map.

 

Hybrid maps:

Creating a hybrid map normally uses the boost compensation technique in the positive boost areas and cell by cell tuning in the off boost areas. To do this the boost compensation graph will have no effect (zero’d out) in the off boost areas and you will change the values in the map itself to get you desired afr for a set load and rpm. Your fuel map should then look something like what is in the attached hybrid map.

 

I hope this makes sense and is right. If it is not then please someone say as I do not want others to be misinformed. The links to the AEM forum also cover more info (especially covering the Mbitsec raw data) however the above is meant as an overview.