Sea Level vs Altitude Tuning

[Power Hungry]

Originally Posted by cleatus12r

The problem with tuning the 7.3L is that there is no table ANYWHERE that sets start of injection. There are numerous factors that come into play and the the SOI tables are just another "modifier". Injection pressure control, engine oil temperature, boost pressure, etc. all play a part in when the PCM DECIDES to initiate SOI. It's not a simple "oh, 7 degrees BTDC is the "timing" and that's it." The PCM bases fueling rates and SOI on a large number of things.

Here's a hint as to why the timing table has a dip in it. Compare the MFD in the "ICP desired" map. See a trend? As the ICP ramps up quickly, the SOI takes a dip. Increased injection pressure actually advances the ignition point of the fuel in the combustion chamber due to better atomization and higher fuel rate (more fuel in less time).

Higher boost pressures in the higher RPM ranges affect the ignition point as well. More boost = higher dynamic compression = earlier ignition point. So therefore, a slightly less advanced SOI.

'Zactly! Especially the part about ICP vs. SOI. Most people don't catch that relationship and then wonder why their engines suddenly become air-cooled.

[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.

[soutthpaw]

How do I view the Maps by Address such as FN1200 I tried to select all, highlighting a single map etc and cannot get the view by address or ID to not be grayed out? for your explanation to make sense I need to look at those FN's and connect the dots, so to speak.
look forward to more of your explanation when u get caught up...

[Power Hungry]

Unfortunately, Addresses and Function IDs are disabled and I don't have any control over that. At some point, I can put the Function IDs in the description/name.

[soutthpaw]

which one is FN1204 the others u named in your previous reply

Also am I correct in thinking that the weird looking maps for stock are somewhat related to Ford trying to optimize for emissions reasons. most of your maps seem to be a lot smoother and more linear curves.. Which seems to make more sense to me...

[Power Hungry]

FN1204 = Start of Injection Delay. The one that looks like it has a valley running through the middle of it. FN1104 is a similarly shaped fuel pulsewidth multiplier table.

As for Ford's reasoning behind the maps, I don't have a reasonable explanation. You do have to consider that their tuning equipment and software was much less advanced than what we have today. When you consider where we are at with tuning nowadays compared to 6 years ago when 7.3L production was halted, the jumpiness of the mapping makes a little more sense, or is at least excusable due to limited development tools. Also, I'm not sure if they were doing steady-state tuning, loaded tuning, or what, but I'm fairly sure that they would plot along certain points in the maps and the fill in the blanks. That's my guess anyway...

[soutthpaw]

Yay! My Mother-in-Law is here so I got to work on the truck today. Got all the O-rings and seals on the oil cooler replaced plus oil change and cooling system flush done...
Now back on topic, I have reread the posts in this thread a few times and it actually starting to make sense Think I am gonna make a flowchart of how the various parameters interact with each other... Will post it once its done...

to do a decel tune, which parameter(s) get the EBPV to close for engine braking? I have the torque converter lockup points done..