I want to know do the gm computers, more specifically 727/730, round the map and rpm values to truncate them

so if you are running at 46kpa and 3150 rpms

does to go to cell 40kpa and 3000rpms - Truncation

or does it round up to 50kpa and down to 3000rpms?

Thanks,
Dan

 

It interpolates linearly between the two (i.e. a straight line).
It is not a Tunercat thing. It is how GM wrote the ECM code.
J

 

I still did not get the answer I am looking for, kind of sounds like it rounds the numbers. What I want to know is if I at running at

so if you are running at 46kpa and 3150 rpms (for example)

what values is it referencing in the tables

 

It may not be the answer you were looking for, but it is the correct answer for your question. The 3D table lookups use 16 point linear interpolation. This thread has a section with an explanation and an example:

https://www.thirdgen.org/techbb2/sho...hreadid=317768

RBob.

 

What there trying to tell you is that both your provided options are wrong. It synthesizes the values it needs based on where you are between the two table values. To dramatically assume the cell on the low side is 1.0 and the high side is 2.0. If you're current location is half way between the 2 cells, then the value is 1.5. If your 25% of the way between them, then the answer is 1.25. Over simplified, but does that help?

 

Looking at the SA table you have 2800 and 3200rpm, 40 and 50kpa. We have 4 cells containing the 46/3150. 3150 is really close to 3200 and far from 2800 so you would probably want to weight the 3200rpm higher than the 2800, same with the 50kpa as apposed to the 40.
Here is the break down of the ~% weight;
The ecm uses those 4 cells weighted like I just showed you to come up with the value whatever formula it uses...
So let's say the values in the 4 tables where as follows;
For 46kpa and 3150rpm the ecm would use;
SA=(.13*11)+(.18*17)+(.32*15)+(.37*18)=15.95degrees.
I think the answer you're really looking for is that you need to modify more than just 1 table value. It's good practice to adjust the surrounding cells to smooth out the table.

 

Gotcha, that was the third option I forgot about. I completly understand.

Sorry about that junkcltr


Thanks to everybody who answered.

Now I gotta go get my GORD running, seems a ford 351 does not like the VE tables for a GM much.