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Fire App. Mech.
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982 Posts
I am glad somebody finally figured this stuff out and wrote it up. This is the kind of info we need to help understand all this voodoo. I for one have never seen a succinct summary of how EGR is calculated, how DPF loading and cleaning cycles are calculated, or anything like that.
 

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Junior Member
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19 Posts
I am glad somebody finally figured this stuff out and wrote it up. This is the kind of info we need to help understand all this voodoo. I for one have never seen a succinct summary of how EGR is calculated, how DPF loading and cleaning cycles are calculated, or anything like that.
The EGR inside the ecm of the CM871 is calculated using an overall FRAC value (measuring from 0.000000 - 1.000000). This value can be monitored inside calterm via paramater [ CBL_EGR_Frac_Cmd ] during a monitoring session. It is derrived mainly by lookup tables, such as the 6 tables representing each cylinder [ C_CBR_EGR_Frac_Alpha0_Table ] - [ C_CBR_EGR_Frac_Chi5_Table ]. The initial value plucked from any given table is based on the current speed (rpm) and fueling rate. From there it goes through some upper/lower limiting filters, gets changed based on exhaust temp, etc. the list is long. The frac command is then sent, along with any derates (combustion changes in this case), to the all mighty combustion manager, where other factors of the engine are sent as well. The combustion manager is actually the application in the ecm that does all the work firing the cylinders, changing fueling and charge pressure rates, etc.

I think where a lot of people get lost in these newer ECM's is that they do not look at them as a multitasking platform. Indeed what is going on in most of them these days, is instead of one big 'program', there is in fact multiple applications running at the same time (think of windows, and several desktop apps running side by side). It makes it very confusing, when looking at 7,000+ paramaters inside an engine in this way, when instead, it needs to be looked at in terms of 'Groups'. When you split these thousands of parms into their perspective groups, it starts to become clearer. Most of these groups have an 'Input', or inputs, to their task, and, ususlly a single 'output', sometimes with branches. Narrow what you are trying to change to this way of thinking, ignoring other similer values not related to the 'Group', and it is much easier to edit the ECM Far beyoned simple hunting and poking around.

good luck,,,...Rawze
 

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Fire App. Mech.
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982 Posts
Sounds like it could also be a recipe for thousands of unintended consequences when the various systems of the engine are running in a combination never thought of by the engineers nor discovered on the test track, and then rushed to market too soon.... (Am I describing 2007 here?)
 

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Junior Member
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19 Posts
Rawze, what can you tell me about 870 isx?
I leave that engine to 'J-DAWG' over on TTR. He has taken the time to figure it out, using many of the settings from my document. I don't own one, so there's not much interest in it for me.
 
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