Cylinder Charge Temp Bias and Charge Temp Multiplier tables - How do they work?

[SteveE]

My set up:
6.0 Gen iv (E38) Swapped into a BMW - 2 bar MAP (converted from 12607218, if that matters?). IAT is being measured in the inlet runner just after the air filter. Tune is speed density only. It has been dyno tuned and the VE table is mapped well enough. Air Fuel Ratio is being measured by a wideband (AFX).

What's happening:
For a month I've been running on the VE table only and observing the AFR changes. (all fuel trims are turned off- short term, long term, decel)
-On a cold morning; say 10 degrees C, it typically reads an AFR of about 14.0
-On a warm afternoon; say 33 degrees C, it reads an AFR of about 14.7
I was expecting a few % of variation, but i'm easily seeing 5% on the same day so something is not right. Curious at first too, because colder air is denser, so for the same fuel delivery one would expect a leaner mixture because the air is denser, but it's the opposite; colder air is creating a richer AFR.

What i'm going to do:
I've searched and one part of the puzzle can be found in the "Cylinder Charge Temperature Bias table". It varies the air charge temperature value used in the VE/Fuel delivery calculation between:
1. Intake Air Temperature value
2. Engine Coolant Temperature value
based on the user adjustable bias value (0-1). Lower numbers biases more towards IAT.
So, right now the PCM is over correcting and that means the bias number needs to increase. So, I've changed the value of the bias by +10% as a starting guess and i'm about to go and experiment.

So what's the problem?
I'm guessing. I don't know the calculation protocols the PCM is using. That means i'm in trial and error mode and it just sucks up time, plus it just sucks not knowing how stuff works.

...and I've noticed another table, the "Charge Temperature Multiplier table", which multiplies the VE table value in relation to the charge temperature. One axis is temperature in Kelvin and the other is the multiplier value and the whole table is currently set with a multiplier value of 1.0. Basically it sitting there doing nothing. I checked some stock tunes and they are all the same - the multiplier value is 1.0

So what's going on? I'm thinking the PCM is already making adjustments in the background based on temperature because the AFR changes, albeit the wrong way, but what is this "Charge Temperature Multiplier table". Is it a secondary table layered on the top of the other built in table which i'm assuming is just based on those standard gas laws we all probably studied in high school which define the relativity of pressure, temperature & pressure?



Has anyone got any experience with these two tables.
1. "Charge Temperature Multiplier"
2. "Cylinder Charge Temperature Bias"
What has your experience been?
...and can anyone say for sure how the calculations are done?
...and does anyone know how the air charge temperature value used normally in the VE/Fuel delivery is done?

It just pisses me off playing around not knowing properly what is going on.

I'll post the outcome of the changes I make to increasing the "Cylinder Charge Temperature Bias " table by 10% and any subsequent changes after that, but it wont be straight away as i have to wait for the weather to change and go through a few cycles.

Anyway, if anyone can help now that would be good.

[ttz06vette]

My set up:
6.0 Gen iv (E38) Swapped into a BMW - 2 bar MAP (converted from 12607218, if that matters?). IAT is being measured in the inlet runner just after the air filter. Tune is speed density only. It has been dyno tuned and the VE table is mapped well enough. Air Fuel Ratio is being measured by a wideband (AFX).

What's happening:
For a month I've been running on the VE table only and observing the AFR changes. (all fuel trims are turned off- short term, long term, decel)
-On a cold morning; say 10 degrees C, it typically reads an AFR of about 14.0
-On a warm afternoon; say 33 degrees C, it reads an AFR of about 14.7
I was expecting a few % of variation, but i'm easily seeing 5% on the same day so something is not right. Curious at first too, because colder air is denser, so for the same fuel delivery one would expect a leaner mixture because the air is denser, but it's the opposite; colder air is creating a richer AFR.

What i'm going to do:
I've searched and one part of the puzzle can be found in the "Cylinder Charge Temperature Bias table". It varies the air charge temperature value used in the VE/Fuel delivery calculation between:
1. Intake Air Temperature value
2. Engine Coolant Temperature value
based on the user adjustable bias value (0-1). Lower numbers biases more towards IAT.
So, right now the PCM is over correcting and that means the bias number needs to increase. So, I've changed the value of the bias by +10% as a starting guess and i'm about to go and experiment.

So what's the problem?
I'm guessing. I don't know the calculation protocols the PCM is using. That means i'm in trial and error mode and it just sucks up time, plus it just sucks not knowing how stuff works.

...and I've noticed another table, the "Charge Temperature Multiplier table", which multiplies the VE table value in relation to the charge temperature. One axis is temperature in Kelvin and the other is the multiplier value and the whole table is currently set with a multiplier value of 1.0. Basically it sitting there doing nothing. I checked some stock tunes and they are all the same - the multiplier value is 1.0

So what's going on? I'm thinking the PCM is already making adjustments in the background based on temperature because the AFR changes, albeit the wrong way, but what is this "Charge Temperature Multiplier table". Is it a secondary table layered on the top of the other built in table which i'm assuming is just based on those standard gas laws we all probably studied in high school which define the relativity of pressure, temperature & pressure?



Has anyone got any experience with these two tables.
1. "Charge Temperature Multiplier"
2. "Cylinder Charge Temperature Bias"
What has your experience been?
...and can anyone say for sure how the calculations are done?
...and does anyone know how the air charge temperature value used normally in the VE/Fuel delivery is done?

It just pisses me off playing around not knowing properly what is going on.

I'll post the outcome of the changes I make to increasing the "Cylinder Charge Temperature Bias " table by 10% and any subsequent changes after that, but it wont be straight away as i have to wait for the weather to change and go through a few cycles.

Anyway, if anyone can help now that would be good.

May want to do a forum search on this topic if you haven't already...been others who have done experimentation with this table. I tried shifting the bias more toward IAT but did not get good results. Ended up going back to stock and focusing on transients. Then again I am MAF tuned.

[schpenxel]

Don't run it in open loop if a 5% change with that big of a temp change is an issue..

What I would do is put the IAT on the intake manifold then use the ZR1 filter/bias tables

I ended up using the injector flow rate vs. IAT multiplier table to correct for temp changes. Works quite well.

[GHuggins]

Is there a set multiplier amount that you use for the IAT multiplier schpenxel? Such as .95 to add 5% fuel or .995 to add 5% fuel? Just wondering because I've found very small changes to this usually makes decent changes to the fueling - just wondering if others see that too?

[SteveE]

This is an update about the changes made to increasing the "Cylinder Charge Temperature Bias " table by 10%. It produced an effect in the right direction:-
Before the change, the AFR swing was typically 0.7 points.
After making the change to the table, the AFR swing is about 0.3 points (Morning temp today was 12C and this afternoon 31C)
OK, that looks positive, so the next step will be to index the table up another 10% to see what happens again.
(And the stumble that typically happens in the first 10 seconds of driving after a cold start due to running a bit lean was not present. Both in the morning and afternoon - Chance? Dunno yet.)

By the way, thanks for the suggestions. I'll keep going with this f this works

[schpenxel]

Is there a set multiplier amount that you use for the IAT multiplier schpenxel? Such as .95 to add 5% fuel or .995 to add 5% fuel? Just wondering because I've found very small changes to this usually makes decent changes to the fueling - just wondering if others see that too?

I haven't gone too crazy with testing it but basically goes from 1.03 at 32*F to 0.94 at 158* and is pretty well smooth in between. Seems to do a pretty decent job of canceling out changes I used to see with temp swings..

[SteveE]

Update 2:
Bias table increased by 20%. Driving along the freeway steady at 102km/h, no incline.
this morning: 16C: AFR 14.33
this afternoon: 32C: AFR 14.37
OK, to be thorough I need to log, but that's one point on the VE table that looks good. For what it's worth, in the tune generally, it felt like the afternoon's AFR readings were a bit higher more often than this morning. To be sure, logging is required, and at a range of temperatures - for Melbourne say 0 to 40C, and when heat soaked, and on cold starts. Feels like for the moment the influence of ambient temperature swings will be reduced because of the changes to the bias table, so I'll put all that extra logging effort on ice and go with this bias table, fine tune the VE table a bit more, the just keep an eye on it. In a few weeks, if nothing strange shows up, I'll switch closed loop back on and revisit it when the season changes, say in May.
Thanks for the input so far. I hope this info might help others.

[BigDaddyCool]

I zeroed out my charge temp tables......... I just use the Injector vs IAT. Its so much faster to sort out that sort of issue. You'll be chasing your tail with those charge temp tables.

[griffincox]

I zeroed out my charge temp tables......... I just use the Injector vs IAT. Its so much faster to sort out that sort of issue. You'll be chasing your tail with those charge temp tables.

With the location of his IAT sensor, this table will provide value.

The closer the IAT sensor is to combustion the less useful and effective this table is.

As mentioned above, one option is move the IAT sensor into the manifold and disable the table.

With the sensor a good ways up the plumbing from the engine this table will be needed IMO

[ERIKGUNNAR]

Hi.

I am N/A in SD tune and ZR 1 bias(0) and filer(1) setting. Do I need to adjust for different weather temperatures. Best to do that at the Charge Temp Mult or on the injector side - Injector vs IAT or no need at all?

[NotSure]

Stumbled on this post in searching for a question related to using an interchiller (uses a/c system) on a PD blower. I don't see a MAT sensor on a GENIV truck application, so if an interchiller, such as activeinterchiller.com sells, what do you tune for? I would not want to tune for the chiller when it is working correctly and then, I dunno, the a/c system fails and true manifold temps jump way up. At least with the standard water to air heat exchanger you will still have some correlation to ambient temp. The chiller, much less.

[NotSure]

I guess this 5 year old post is where I should have went to, just found it.

https://www.hptuners.com/forum/showt...hlight=chiller

[07GTS]

manifold temp is the average between ECT and IAT on the bias table, if its zeroed out and IAT in after blower in manifold then that is the same figure used for manifold temp, any number grater then zero in bias it starts to calculate with ECT also, but if ur blown with IAT in manifold set to all zero