Air Density Adjust

[AH64ID]

What does everyone do with these?

How does the ECM average the tables between base and each Air Density table?

Thanks..

[Dmaxink]

I leave mine stock (assuming your talking about table [E2554])...this table is a reference back to the other 1-4 timing tables as a reference of your altitude. So if your sea level (14.69 baro) you would be in table 1..rather it is in reference to timing or fuel pressure... I actually set all my tables up the same base, 1-4.

[DoghouseDiesel]

I do tweak mine to more realistic levels as the factory ones are pretty far out there.

What I look at for air density is this. Make the tune for where you live, so like Kory said, you CAN pretty much make all the tables (1-4) the same, if you want. MOST of us don't travel that far from home and MOST of us don't go up or down more than 4000 ft to make that much of a difference anyways.....at least here on the east coast anyways.

Factory tune...yeah, they gotta vary it quite a bit because they have to fit such a wide spectrum of operating environments.

My air density gets calculated for approx 500' and I vary the temperature between 20 - 110*. That should cover me all year and I can go from here back home to NY and not have any major issues.

For MY tune in the MY truck, most of my air density is calculated between .068 - .080

[AH64ID]

So if in a given year I drive my truck from sea level to 9K feet and vary in temps from -10° to 110° I should probably not have 1-4 the same?

Just trying to understand some of the tables better.

Thanks!

[comnrailpwr]

Correct, if your driving differs that much u need to adjust all tables to accomidate your desired adjustments. otherwise it will reference back to stock during altitude changes.

Jake

[Dmaxink]

Maybe i misunderstood you Jake, but when the altitude changes.. it will just go on to the other table that represents its current density. Here is one thing to think of....typically it is our lower baro pressures that require the lower timing...so say if your 50%btdc timing (or whatever) works (no rattle) at low altitude..chances are you will not have problem at higher altitudes. At least in my experience...

[DoghouseDiesel]

So if in a given year I drive my truck from sea level to 9K feet and vary in temps from -10° to 110° I should probably not have 1-4 the same?

Just trying to understand some of the tables better.

Thanks!

Correct.

The more varied the environment your truck gets used in, the more varied those tables will need to be to compensate for it.

Hell, you're a pilot, I know I don't have to explain air density altitude and all that BS....you outta be explaining that here.

If you look in the "Gift Tune" I posted, you'll see that all those tables are the same. Simply becuase that tune gets used here in Alabama and that truck really goes no where else except from Atlanta to Panama City, FL and the air density only changes by a maximum of about .012.....MAX

[AH64ID]

So if there is a base table and 4 altitude tables, does it blend the base and appropriate altitude table?

[DoghouseDiesel]

No, it will use one table at a time.

The only thing the ECM knows is the data it's fed. If the sensors says the density is .XXX, it doesn't look 1/4 mile up the road and see that we're still going up a hill and have the next map ready.

If it was trying to use multiple tables for the same data it would be getting mixed signals.

Let's think of the Cummins ECM like a man.....one track mind. It's time for breakfast, let's eat breakfast, no idea yet what I want for dinner. :grin:

[comnrailpwr]

Maybe i misunderstood you Jake, but when the altitude changes.. it will just go on to the other table that represents its current density. Here is one thing to think of....typically it is our lower baro pressures that require the lower timing...so say if your 50%btdc timing (or whatever) works (no rattle) at low altitude..chances are you will not have problem at higher altitudes. At least in my experience...

I was basically saying if he builds a tune for say sea level and doesn't touch adjustment in say table 4. his adjustments will not be present when he hits 9k feet because The ecm will take the commands from the unadjusted table, 4 in this example. I think I'm right, the truck I tune stays local and made them the same. But while we're on this whats the point of a base table if It'll always be using one of the altitude adjustment tables? Do we know when its using which one because I when efilive first came out I saw smartys tablets and I think theirs were stock? How would that work when that tune would change altitude? The smartys timing doesn't revert to stock upon altitude changes.. maybe I'm wrong and they were modified, haven't seen one in a while.

Jake

[Dmaxink]

Jake, i gotcha now bud.:cheers:

Rich, I understand density tables and do not disagree with you...but is my statement incorrect in saying if we are going for a certain % at sea level..that it should not do as well @ 9k? I know at least in dmax world i had no issue running the same table from here to there... I'm completely understand that this may not work in others applications as each truck is different...

I could see the event of a guy running very conservative timing wanting to step it up as alt changes...but generally everyone is going for the most efficient "higher timing" setup...

[DoghouseDiesel]

Kory, you are correct.

The biggest problem with not correcting for altitude is going to be a dirty tune and higher EGT's.

The truck is going to perform regardless. Bottom line, you're making your own atmosphere with a turbo anyway so its no nearly as critical as it is on a NA gas motor. But, for the sake of fuel economy and just plain good tuning, you'd want those tables adjusted.

Without actually living and testing in one of those places, it'd be hard to do. It's a lot easier for a manufacturer that trlests all over the place to collect that data tha ln it is for us to build a hypothetical table.

It's like we talked about with the different size injectors. There are ways to compensate for them and we all do it, but it takes a little dialing in on the receiving end to get it right on.

[comnrailpwr]

Makes sense les, never thought about us creating our own atmosphere being turbocharged.

Jake

[DoghouseDiesel]

You are creating you own atmosphere, but still, less oxygen is less oxgen. We're just much less susceptible to bad air. / fuel ratios than gas motors are.

A diesel may range from 125:1 at idle to 18:1 at peak power where a gas more needs to stay in a very narrow 10.5:1 - 17:1 to run at all and even narrower to run correctly.

A small variation in the AF ratio isn't going to effect a diesel very much, as long as you're not going too heavy on the rich side.

That's what trips gas guys out at the track when my hood is up. 1 - they have no clue what they're looking at and 2 - when they see 2 turbos and the nitrous they think you're gonna burn a hole in a piston and you have to get into the whole long discussion about diesels being polar opposites of gas motors.

[2007 5.9]

How does one determine density?? I live at sea level 14.5-.7...I frequent Tahoe 7500ft...how do I know the density in Tahoe so I can adjust accordingly??

~Les

[DoghouseDiesel]

Density is roughly based on temperature and pressure.

There are a bunch of calculators out there that all you have to do is punch in your altitudes and temps and they give you the densities.

Just google air density calculator and you'll get a 100 of them. You'll also get a few that pop up with the actual formula if you want to hand jam it.

[AH64ID]

I guess I'm still confused about the relationship between the base table and the air density adjust tables. This is from the base table "Start of Main Injection base table. These values will then be further adjusted by the air density adjustment tables.
"

The you to air density table select pages and there is nowhere it talks about using the base table.. So looking at the verbage on base table page it looks like the air density adjust is a mix from base and air density adjust, but you guys are saying they don't mix... Is base table ever used?

[DoghouseDiesel]

Give me a little bit, it'll be easier to show with screen shots than it will to explain....

[DoghouseDiesel]

Okay, this is going to take me a few.

I'm kind of doing this along my EFILive for Dummies style, but I'm building an Air Density chart from -20 to 120 degrees and from sea level to 10000 feet, so give me a few minutes.

[killerbee]

Don't know if this will help, a link to a non-cummins application with calculations. The atmospheric part is no different. There are 3 pages, tabs, to this spreadsheet, fyi.

http://killerbeeperformance.com/download/thermal_feedback_lly/Turbo%20Calc%20spreadsheet.xls

[DoghouseDiesel]

Okay, first, before we start looking at how the tables are used, we have to ask ARE they even used. To see if they are used, first lets look at just what we are dealing with as far as air density goes.

Please keep in mind, this chart is DRY air density. It does not take into account dew point, relitive humidity, etc....so all you pilots out there, don't smack me in the knee caps.

This is your air density. I put this together from sea level to 10,000 feet and from -20* F to 120 F. What you see with some of the colorations are where you'll see some pretty significant power gains or losses if not adjusted for, especially in a naturally aspirated motor. Our don't get quite as badly affected, but they are affected none the less. The areas you see in the darkest green are the areas that if a vehicle is placed on a dyno, would fall within SAE correction numbers for density (sea level and 68*), which is around .075. As you can see, the colder and lower you are, the denser the air is. Hot and high is not your friend.

http://i288.photobucket.com/albums/ll189/Cumminalong/Dohouse Diesel Pics/EFI Live Screen Shots/Slide1-19.jpg

The screen shots below are from an OEM file simply so we are looking at a common file.

Now, how do these number relate to the air density tables that the ECM uses. Actually, they relate VERY little.....at least for the OEM tables. The tables are so far out of whack, other than the base table and table 1, which are almost identical, than the other tables are on the extreme ends of the spectrum (hot and high) and don't get used very much, if ever.

Here are the fuel limiters for the base tables and tables 1 - 4. Look at the curves for the base table and table 1. Look at the table....same thing.

http://i288.photobucket.com/albums/ll189/Cumminalong/Dohouse Diesel Pics/EFI Live Screen Shots/Slide4-7.jpg

Now, look at the selection criteria for the tables. The selection criteria is completely skewed to table 1 and VERY small part to table 2. Tables 3 and 4 are Mt McKinley dropped in Death Valley. Table 4 actually doesn't even register on the chart I built. So, to answer the original question, yes, the base table does get used, but 99% of the time, unless you've modified the selection criteria, you're in table 1. But if you look at the chart below, if you didn't know how to interpret the air denisty, you would think you were using table 4 a lot, which you would probably never use once in the trucks life span.

http://i288.photobucket.com/albums/ll189/Cumminalong/Dohouse Diesel Pics/EFI Live Screen Shots/Slide2-19.jpg

http://i288.photobucket.com/albums/ll189/Cumminalong/Dohouse Diesel Pics/EFI Live Screen Shots/Slide3-9.jpg

[DoghouseDiesel]

Here is the air density chart in PDF format that I did if anyone wants it.

Please double check the numbers.....there's a reason I'm working at home today.

[killerbee]

That was a nice approach, and rationalle.

These are what we used to call, "peripheral" algorithms. Meaning they don't concern the mainstream power tuning audience, if they don't impact the track time. The point I am making, is that as EFILive exposes parts of the ECM, they have not always been validated as working. We came across some of these, for example, 3 years after the 04 dmax OS was supported. It is not a criticism, just some beta facts of life: nobody cared, until somebody cared, and evolution depends on the end user not assuming too much.

Consider validating the tables with experimental settings, before assuming that they are functioning.

Air density is pretty important to everything, IMO...timing, and boost especially. It can be very easy to destroy the turbo at 10,000 ft, with numbers it is otherwise happy with at sea level.

[AH64ID]

Thanks guys.. think it's getting a little more clear.

[06redram]

I remapped my air density setting for my zone. It works great for this hot and cool weather we are having. Truck no longer changes with the weather. Thanks to DogHouse :)

[06redram]

Screen shoot of how I setup my air density table:
http://tapatalk.com/mu/601a5f88-1156-6b06.jpg
http://tapatalk.com/mu/601a5f88-1283-f626.jpg

[DoghouseDiesel]

Sweet!

Glad it's working for ya.

The factory map is WAY out of whack.

[06redram]

It is way off the map! Big thanks again I hope the screen shoot are ok to put up to help others