Sea Level vs Altitude Tuning

[soutthpaw]

Ok I think I am gonna leave all the WHY questions to you now Cody.. then at some point I am going to put them all in one thread and get Jack to make them a sticky... Excellent explanation as usual. I give it

As for my previous post, It looks like the Timing is an actual setting and not a modifier? that's why I thought it should be different for each different map... Here is the Stock sea level vs altitude map

The part that is Highlighted in yellow I thought was interesting.. Reason being is that we know the burn(Combustion) time is a constant at the selected altitude.. so if the engine is turning faster you should need to start the Burn earlier given the same amount of fuel. Right?
so why does the stock setting retard the timing so much in the higher RPM's in that sea level map.. also it seems like there is a mid RPM range that requires retarding the timing a bit that I am wondering the reasoning behind it (is there another modifier somewhere in the parameters that justifies the retarding of the timing that I am missing)

[cleatus12r]

Originally Posted by soutthpaw

Ok I think I am gonna leave all the WHY questions to you now Cody.. then at some point I am going to put them all in one thread and get Jack to make them a sticky... Excellent explanation as usual. I give it

As for my previous post, It looks like the Timing is an actual setting and not a modifier? that's why I thought it should be different for each different map... Here is the Stock sea level vs altitude map

...........we know the burn(Combustion) time is a constant at the selected altitude.. so if the engine is turning faster you should need to start the Burn earlier given the same amount of fuel. Right?
so why does the stock setting retard the timing so much in the higher RPM's in that sea level map.. also it seems like there is a mid RPM range that requires retarding the timing a bit that I am wondering the reasoning behind it (is there another modifier somewhere in the parameters that justifies the retarding of the timing that I am missing)

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.

[soutthpaw]

here is a table I Just made that compares the Offset at altitude compared to sea level of the stock map as a way to look at different patterns.. I may put these values on a map just to see what it looks like in 3D


The highest advance group is at high RPM in the low to mid throttle range Based on the fact that there is a low mass fuel desired value (found in low torque demand situation).. which would most likely be found at high crusing speed... thus more advance under low load and best fuel efficency
oh the 55/2200 value is a typo, its supposed to be 9 not 90 heh

[soutthpaw]

Ok, got out for a test drive this afternoon... the up down shifting issue is gone on both the tune Cody sent me and the one I made. both r are good except both and I even noticed it a bit in the 80HP tune what the the on mild acceleration the Torque Converter is a bit too firm when it locks. still tugs a bit when it locks in 3RD gear ONLY.... so need to figure out how to soften that one lockup then will be good to go.

The other tranny tune I did locking in all gears turned out to require a lot more pedal to move the vehicle than the other 2 tunes that i test ran so I think I would have to change the RPM to Mass Fuel Desired level and maybe the inferred pedal position to get it to work right... also the 1-2 and 2-3 were pretty harsh so need to soften those too... do i lengthen the lockup time or the slip time? it i want the converter to be locked as soon as it upshifts? ill try that later

[cleatus12r]

I'm glad you got it figured out.

If you're still having issues with the firm TC lockup, look at the torque table in the RPM range in which it's giving you fits. I didn't mess with that map at anything above 2000 RPM if I recall...and it's pretty close to stock there along with the Lockup DC%.

[soutthpaw]

Edit: I answered my own question regarding Pedal position and it didn't work just gave me DTC for low throttle position etc

[cleatus12r]

You have a PM, DJ.

[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...