Thread: IAT Density Correction

so im not really good with math an stuff an im having a hard time figuring out whats up with the numbers in the boxes for this...

so what i want to do is add or remove fuel at certain intake temps at certain rpms and loads.. but im not sure what to do?

if i dont use the iat density correction thing do i just add some fuel to the box above it? but wouldnt that blanket the whole tune making everything richer? i did enable it for a short time but i couldnt really tell what was happening.. it seemed to make be super lean or super rich an i just disabled it..

lol i thought speed density was suppose to make tuning easier? sure doesn't seem like it as i am very confused haha!

i've got the maf stuff down for the most part, it runs great on maf cold or warm an gets good mpg's

i know its a temp thing too, earlier when it was warmer i had low to mid 11's AFR, tonight on the way home it was much cooler an was getting low 12's

IAT density correction provides a means to apply a portion of ECT to the IAT measurement to more precisely calculate the actual temperature of the air entering the combustion chamber.
The calculation is:
density corrected IAT = (IAT x factor) + (ECT x (1 - factor))

Example1:
IAT = 80ºF
ECT = 170ºF
density correction factor 100% (from table)
density corrected IAT = (80 x (100/100)) + (170 x (1 - (100/100))) = (80 x 1) + (170 x 0) = 80º

So this means that 100% of the IAT and 0% of ECT is used to calculate density corrected IAT.

Example2:
IAT = 80ºF
ECT = 170ºF
density correction factor 50% (from table)
density corrected IAT = (80 x (50/100)) + (170 x (1 - (50/100))) = (80 x 0.5) + (170 x 0.5) = 40 + 85 = 125º

So this means that 50% of the IAT and 50% of ECT is used to calculate density corrected IAT.

The density corrected IAT is used as the index for the "IAT FUEL TRIM", "IAT IGNITION TRIM", and "IAT DUTY COMPENSATION" tables AND for the IAT trigger values for outputs.

The IAT DENSITY CORRECTION table will need to be tuned for your particular setup. Basically, when the air is moving more quickly (RPM) and at higher pressure (MAP) through the intake manifold, it will pick up less of the ECT heat and therefore the table value will be larger, so a larger percentage of the measured IAT will be used to calculate density corrected IAT.

Dave

Sounds like a better name for this would be something like "Coolant temp corrected IAT"?

hmmm. good info dave thanks for takin time to post that.. however im still quite confused maybe i should just stick to tuning mafs and just use the map/iat as additional information. i was really excited when i found out that this was suppose to be easier to tune then maf, but i dont think thats true at all.. atleast not for newbs like me.

ok i've been thinking and reading an tryin to absorb info...

so at lower rpm and boost or vacuum (slower air speeds) the air has more time to soak in heat from the piping and manifold, Thus will not need as much adjustment as it would at a higher rpm/boost (faster air speeds) where the engines actually using that colder air?

also, the smaller the number the less of the iat readings are being used with ect readings so less adjustment for the ecu?

i think im catching on, i've been reading all over the place tryin to grasp the concept.. it seems that most the stuff your talkin about is also used in other programs/tuning stuff. albeit named differently

It is all in what you are use to tuning .. Speed Density is a lot easier for most people to catch onto because your load values are real world values and are something that you can relate to.

Now, if you are expecting your fuel map to look anything similar then you will have problems.

The best way to go about tuning a speed density fuel table is to keep everything as smooth as you can and make sure you do not have any intersecting fuel lines in your 2D graph. The 2D graph is actually a VERY VERY useful tool when tuning and smoothing out a speed density fuel table and will definitely be helpful to you. If you check out the example speed density fuel maps, you will see what I am talking about there.

NOW, when it comes down to the IAT density correction table .. you don't have to enable this. If you are unsure of how/where to apply it, just leave it disabled and use the regular IAT fuel/ign trims.

But if you want to experiment with it, by all means let use know if you have any other questions.

ok i see what you mean about the 2d graph, thats neat that you can click an drag the little boxes, or use the arrow and +/- keys..

i had a hell of a time untangling those, you gotta make sure that the boxes are in order an shit so when you go up an down through the load it doesn't skip around, it hits each box in order.. i just went from left to right making sure each one was in the correct load spot and that it was fairly smooth.. i havent tested this one out yet tho as it was ALOT easier to do on my pc then my laptop hahaha

here's a pic..



however im having this issue where all of the sudden for what seems to be no reason at all the lines will criss cross on me again and tangle up like a giant ball of christmas lights.. then im back to untangling them its done it on my pc and laptop.. whats even more weird is i can have saved it with everything smooth and when it goes all wonky i can reload it from when i saved it when it was good and its still all fucked up, not sure whats going on there..

You may need to click back onto the fuel table and change a value on the table for it to save, I will look into that though!

Its not reverting to a previous state, it actually changes numbers in several boxes on its own and really tangles the lines up worse then it was and I cant reproduce whats happening it just seems to do it at will lol

I think what is happening is you are selecting more than 1 box at a time, you can verify this by watching the changes you make on the graph while also viewing the table.

I tried to replicate what you are saying and haven't had any issues editing the graph and/or the table together.

I would also say that you might want to try using the "-/+" keys and not dragging right on the graph itself.