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.

[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