Variables of Ignition Timing in a Stock TJ

[SSTJ]

Here are some examples from a 1997 XJ JTEC PCM:

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I wonder if I'm interpreting these cells correctly.

For the two RPM-vs-MAP tables, the numbers are larger and are all positive, so I think these are absolute—meaning "X degrees of rotation before top dead center (BTDC)".

For the MAP-vs-IAT and MAP-vs-ECT tables, the numbers are both positive and negative, and are relatively smaller. So I suspect that these are relative—meaning, "shift the base table by X degrees of rotation".

 

[TEZZA]

I wonder if I'm interpreting these cells correctly.

For the two RPM-vs-MAP tables, the numbers are larger and are all positive, so I think these are absolute—meaning "X degrees of rotation before top dead center (BTDC)".

For the MAP-vs-IAT and MAP-vs-ECT tables, the numbers are both positive and negative, and are relatively smaller. So I suspect that these are relative—meaning, "shift the base table by X degrees of rotation".

Yes.

 

[SSTJ]

I've updated the original post with my understanding so far.

 

[SkylinesSuck]

I think you are getting your head wrapped around it (at least as far as I understand it but I am no expert). I think having a broad understanding of the inputs and their affects is important, but also a large part of tuning is experience on both the platform and with the specific vehicle. After watching a couple of different tuners do their thing first hand, I think it's equal parts experience and voodoo with a splash of trial and error thrown in for good measure. But if you don't know what affects what, you'll always be chasing things in the wrong direction, or in the right direction but for the wrong reasons.