# Modelled fuel - What does the IAT correction table do?

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Hey,

So for modelled fuel, the charge correction function is part of the equation.

But this needs to know IAT, so its already part of the equation.

So for the IAT correction table, should this be left blank? Or is it redundant on modelled fuel. Or does it just trim it even further.
Should I have IAT correction just turned off?
Thanks.

Edited by Davidv
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Normaly/theoreticaly set to zero. But it might be nessesairy to have some small adjustments on it anyway. Same applies to the warmupenrichment.

(When chargetemp approximation is on)

If you need some ideas on how to tune the chargetemp correction table look over at hpacademy.com. There was a webinar not to long ago on this

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The Main purpose of this feature is to control the fuel better when the air is at a slower velocity through the intake system. Some cars have Composite intake manifolds while others have Cast Aluminum type. The air while at slower speed tends to grab the latent heat. This can cause the IAT to heat soak and the values for the correction may start to change as the air speeds up. But the IAT may not always react as fast as we need it to. So we have this algorithm that allows us to manipulate how the ECU calculates the multiplier for IAT and ECT. A higher velocity of air through the intake system (depending on the type) will have a better fuel calculation for charge temp. via IAT as it does not soak as much heat and is more consistent (i.e ECU can calculate the charge temp. much better). When there is very low velocity of air through the intake system. We tend to look at ECT for our fuel charge temp. corrections as the ecu knows that there will most likely be more heat for the Charge temperature. Each car and system tends to be different in the 3D table for this function.

I have tuned multiple cars using this and find that in traditional mode. You will see the car no matter how close you get it in closed loop every so often shifting -5 +5 on fuel trim depending on the day. Which is not a bad thing. But when I have done the Modeled equation you can get very close and it is very accurate when setup properly. The only thing I wish we could have added is a little more resolution in the 3d table to change the values of X and Y axis. Especially when tuning twin charged vehicles.

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Thanks,

The reason that I ask is that since changing to modelled fuel, I cleared the values in the IAT correction table and have been expecting the car to run leaner when cold & vice versa. As I was looking to build my own IAT compensation table, by seeing how the car actually reacts without it.

But I have been experiencing very slightly the opposite!

However if IAT correction is indeed built in even when the table is blank, then this makes sense.

Modelled fuel is pretty awesome, I initially managed to get the car running nice enough to drive just from a guesstimate basemap.

Edited by Davidv
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Just to add to what Rich and Steve have said. If you are using any value in the Charge temp approximation table, other than 100, then the current IAT value is having an effect on the fueling. If the charge temp table is set up perfectly then the warm-up enrichment table and IAT fuel trim table are not required, meaning they can be zeroed out. However they are available for use, and as the axis are configurable they could even be used for purposes other than originally intended.

Scott

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Hi Scott,

the documentation says

"Normally the higher the engine speed the lower the value needed in the charge temp table. Also the higher the engine load (MGP or TPS) the lower the value needed in the charge temp table."

I'm running ITBs (no MAP sensor) and I was wondering how I could change the load axis to TPS. The context menu item "Axis Setup" is diabled.

Or does it make no sense to use this function when using "Modelled" mode with "Load=BAP" ?

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Hi Fant,

It does make sense to change the load axis on the charge temp table to TPS in your situation. Unfortunately this is not something that can be done due to current firmware/PCLink design, a request has been put in with the engineering team to change this.

The best option for now is going to be for you to put the same value in each column (engine speed) regardless of MGP), this will make the charge temp table behave as a 2D table dependent only on the current engine speed.

Scott

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• 2 years later...
On 6/21/2016 at 3:39 AM, Scott said:

Hi Fant,

It does make sense to change the load axis on the charge temp table to TPS in your situation. Unfortunately this is not something that can be done due to current firmware/PCLink design, a request has been put in with the engineering team to change this.

Scott

Hi Scott, has the engineering team done anything about it yet?

Fant

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