BLM behavior linked to CCP in EE
here's the story and all i know about it so far
EE uses RPM vs MAP as boundaries for BLM cells instead of what i'm used to (RPM vs AFGS) for regular driving operation.
this is probably because it's dual purpose closed loop maf and speed density, so long terms can be used in either mode. cells 0 through 15 are used for regular driving
there are three other "special" cells that have always been a bit mysterious
what was previously thought:
- cell 16 is activated @ closed tps at 0 VSS (stopped idling)
- 17 is used for closed tps at >0 VSS (rolling idle or decel)
- cell 18 is preferred when the EGR is at higher duty cycles or something like that
although the behavior ends up matching those specs, the reasoning behind it has proven to be possibly incorrect
the code actually enters these cells based on CCP duty cycle (not tps) when the CCP system is below a certain duty cycle. this just happens to coincide with low TPS, since the CCP appears to be largely TPS based. the correlation between ccp duty cycle and switching to cells >15 is consistent
it also explains why ordinary BLM cells are never used while the car is still warming up, and the CCP enable temperature hasn't been reached yet. it also explains why raising the CCP enable temperature out of operating range will leave the blm system stuck in cells 16-18.
the duty cycle threshold at which it switches from 'regular cells' to 'special cells' is actually a previously unknown tuneable constant, which will be going into the next revision of tunercat's definition file. the guy from tunercat has helped me figure some of this out too, so thanks a lot to him. we've found moving this duty cycle threshold to zero will cause cells 16-18 to never be used under any condition.
there is also a (fairly undocumented) transient fueling map that the LT1 has, that is rumored to have corrections in it to account for the unmetered air of the CCP duty cycle.
my theory is that the programmers wanted seperate learn modes for when the transient fuel map is enabled or disabled, as it would create bad averages otherwise, and that's why the special cells were created. only 3 cells were necessary for the alternate mode, since the ccp is only inactive during warm-up and closed TPS. apparently tunercat will have the ability to disable this map in its next revision too
tune-by-mail guys have known about the transient fueling map for years, evidenced by the fact that i found it was already disabled in a binary that i got from a certain tuner... but was enabled in all the stock bins available.
most other closed loop PCMS dont have those special cells, and have no problem learning idle and decel. perhaps its because they dont have a transient fueling map like the LT1 does... or maybe they really wanted special idle and decel cells, and this was a convenient way to code it?
could anyone offer any more info?
