[Power Hungry]

Okay... time to wear my fingers out.

The first thing you may notice is that the SOI table (fn1200) is curved while the altitude table (fn1201) is (more or less) linear. This is because fn1201 is an altitude adder to the base SOI. The amount added is not constant, but instead is a percentage value based on altitude. To be honest, I don't have a definite explanation on how the percentage is calculated in relation to altitude which is why in most cases I leave it alone and work with fn1200 instead. I'd be inclined to think that calibrations that have had to remove timing when dropping to sea-level may have had both tables modified and the PCM could no longer compensate for the change in altitude.

The "dip" in the main SOI (fn1200) map, as Cody indicated, is because of the inherent shift in SOI due to the increase in injection pressures. It is quite complex how all the maps interrelate with each other and overlooking any one component in the process can result in catastrophic failure. This is why I try to keep changes as simple and as few as possible.

Consider this...

10 years ago the only changes we made to diesel calibrations were functions 1104 and 1204 and we made 100 HP. Many people in the tuning business complain that this is NOT the way to tune engines. Part of me agrees, and part of me disagrees. The agreement comes from the fact that there is no RPM compensation for SOI so you may end up with excessive SOI at lower RPMs in order to achieve the desired SOI at higher RPMs.

The benefits from using these tables are quite clear. Since these tables are related to EOT, you can easily control at what temperatures the modified power curve comes on and this helps prevent excessive power output when the engine is below operating temperature. Also, since the fuel table (fn1104) is curved based on ICP, you can maintain a stock profile at idle/low throttle and progressively curve the fuel delivery based on driver demand.

There is no clear cut explanation on how to properly handle tuning these processors because the dynamics of tuning these engines is a bit more complex than people realize. P-pumped engines have much fewer tuning issues because the relative pressure of the injected fuel doesn't vary nearly as much and the timing curve is constant. Of course, P-pumps are louder throughout the RPM range while HEUI engines are relative quiet in comparison.

Anyway, I hope this helps a little bit. I'll get a bit more involved in this discussion as I get caught up on orders.

Take care.