Density & Transient Tables?

[super_kev]

Hi all,
I'm new to HPT, so forgive the ignorance but I can't find a solid answer. On the cummins (I've got a '07 5.9) when looking through HPT (running 3.4.23 currently) I see transient tables for fueling and timing (I'm sure they are elsewhere as well). What are these and how does the ECM relate them to other tables?

The only piece of the puzzle I found is that one user said that he heard most tuners put their tune in transient and copy/paste it to a couple other tables as they are most frequently used. Is the transient just used until engine is warmed up (and if so, what is "warm-up" parameter controlled by? ECT?) and then it switches to a non-transient table? How does the ECM select the proper density table?

Thanks for the help.

[Jim P]

Transient tables are used under a wide load change. Not sure specifically how wide of a load change. On my 05 it uses the lowest air density tables during startup and high/extended idle runtime.

[super_kev]

Is there a way when logging with the MPVI interface that one can see when the different tables are commanded?

[Jim P]

I use the smarty touch and UDC Pro, with that it does log and tell you on the display which map it uses. Transient will be used during large swings in load, etc. other than that you will be in the high air density map when at steady. I have noticed it uses the lowest air density map during cranking and during high/extended idle.

[Jim P]

Chances are during your normal driving you?ll never actually use any map other than transient and high air density. Most people just make them the same so the ecm more or less is doing what they want at all times rather then switching back and forth between the transient and high air density maps getting different values from what they are desiring at a given time.

[super_kev]

Thanks for your input Jim. Found this thread over at CF with some more discussion about how/when it's selected. Perhaps I'm a bit dense, but it finally made sense to me when I also found the ECM7590 - Airflow Density Range table (under Airflow - General) showing what was selected starting at what density. For future search results, here is the thread in question - altitude tuning question by steve05ram360 (who is also on this board): http://www.cumminsforum.com/forum/3r...-question.html

[Jim P]

Yea I?m not sure how HPTuners VCM is laid out and what they call all the maps and everything but basically the ecm uses barometric temperature and air temperature to get rough determination of the air density, I say rough because the ecm doesn?t take other factors such as humidity and dew point into account, which does have an effect on the air density. It then compares that determined air density to the ?air density select table? to see which air density table is being commanded for that given air density and uses the selected commanded table for your timing, rail pressure, etc. That air density it determines is also used in other limiter tables.