MAF Scaling - Open/Closed Loop Fueling info

[jvincent]

Sorry, should have added my configuration info.

Stock intake and an OFH. No leaks, since generally things are pretty stable, other that right at that particular load point.

I was trying to figure out which MAF scale to start with as my baseline and noticed the odd behaviour in LTFT, which is when I looked at the MAF table and noticed the voltage scale.

If you look at the scale there are a lot of data points where it is fairly linear and then they actually get further apart (x-axis) right at the knee of the curve. Since we are interpolating data I would want it the other way around.

[thambu19]

@steve99
Any idea why the Takeda MAF scaling isnt proportional all the way? It seems to have a kink half way through. Does not look right to me. If the throttle body diameter or the higher flow rate through a better filter element is causing the higher flow it should show that delta all the way through the range

[phrosty]

Originally Posted by thambu19

@steve99
Any idea why the Takeda MAF scaling isnt proportional all the way? It seems to have a kink half way through. Does not look right to me. If the throttle body diameter or the higher flow rate through a better filter element is causing the higher flow it should show that delta all the way through the range

Scale those parts in CL only and the lump should go away.

[thambu19]

Originally Posted by phrosty

Scale those parts in CL only and the lump should go away.

you mean the scaling only needs to be done for the CL region? What about the OL region then?

[solidONE]

Originally Posted by thambu19

@steve99
Any idea why the Takeda MAF scaling isnt proportional all the way? It seems to have a kink half way through. Does not look right to me. If the throttle body diameter or the higher flow rate through a better filter element is causing the higher flow it should show that delta all the way through the range

The load limits need to be adjusted. With the unmodified load limit tables you will just about always get that lump in the 2.7~3.0 range due it it being the bottom bottom range of OL voltages. Load limits need to be raised to bring up the AFR at that range under OL operation.

[thambu19]

Originally Posted by solidONE

The load limits need to be adjusted. With the unmodified load limit tables you will just about always get that lump in the 2.7~3.0 range due it it being the bottom bottom range of OL voltages. Load limits need to be raised to bring up the AFR at that range under OL operation.

Is this because the Takeda intake has a larger diameter tubing at the MAF location and hence underreports voltage?

[solidONE]

Originally Posted by thambu19

Is this because the Takeda intake has a larger diameter tubing at the MAF location and hence underreports voltage?

I don't think so, although the difference in diameter and lack of air straightener will require different maf scaling and may end up with lower voltages as you said.

That lump is there to compensate for the insufficient fueling cause by too low of a value in the load limit tables under OL operation. Since the load limit will cap the lookup for fueling at say 1.1 g/rev on the OL fueling table, when the actual loads being seen are likely higher (maybe 1.2 g/rev) causing the AFR's to go lean in high load OL operation compared to mid/low load CL operation with the same voltages. So, when you put that lump in the maf scale to compensate it ends up being too rich under CL operation.

From Wayno's thread: http://www.ft86club.com/forums/showthread.php?t=94822



If you look at the load limit values comparing the stock load limit table with the modified ones below it you will notice that they are higher than the stock table from around 3000rpms. And if you were to take a WOT log you will also notice that the MAF voltages where that lump in the table you posted is, it would also be right around 3000rpms. Raising the load limit at that range will allow the computer to look up a richer value on the OL fuel table thus not requiring you to up the MAF scale to compensate.

On my car, which only has an drop in filter panel, the MAF scale will also end up looking a lot like the one you posted with that lump, if I kept the stock load limit tables.

Sorry if I'm not too good at explaining things. lol maybe one of the other guys will chime in with a better explanation.

[thambu19]

@solidONE
So if someone bolts on the Takeda intake without any MAF scaling does the LTFT go +ve or -ve and by how much overall?
I sort of understand the concept a but but perhaps the answer to the above question can make me understand better.

[thambu19]

Under which section of the OFT xml does the load limit table reside? I can't seem to find it. Sorry

[jvincent]

You need to use Wayno's defs to see the load limit tables.

[steve99]

Originally Posted by thambu19

@solidONE
So if someone bolts on the Takeda intake without any MAF scaling does the LTFT go +ve or -ve and by how much overall?
I sort of understand the concept a but but perhaps the answer to the above question can make me understand better.

I posted up some baseline Takeda scaling in the first post in this thread

From memory the guy was getting fuel trims of aprox 15% before i did some quick scaling for him got it down to about 5% .

MAF sensors dont measure the entire quantity of air passing through the intake. They take a sample and then this is used to estimate the total flow of air.

Hence if the size of the tube the maf sensor sits in changes, or even the flow of air past the maf due to its positioning in air flow stream or turbulent flow all effect what maf "sees".

Each intake type is different and just because to have to move the maf scaling up/down does not necessarily mean the intake is flowing more or less, it could just be the positioning of sensor has effected the sample "seen" by the maf sensor to estimate the total air flow.

The MAF reading is then used as an input to generate the "engine load" parameter which is used in many ECU tables to determine ignition timing/fueling and cam timing etc applied at different loads.

So if maf is off it can effect many engine parameters.

[thambu19]

@solidONE
I think I get it now. So there are two ways of making sure the AFR is right. 1. Adjust the MAF with a bump at 3.0V ish or 2. Increase load limit at around 3K rpm.

This is done because if not done the engine will run lean at 3K ish rpm. What about the other engine speeds then? Why would it not run lean at those? Is it because at the other engine speeds the load limit isnt clipping yet? Meaning to say that at 3K rpm the intake performs better than at other rpm?

Would you have a copy of @Wayno xml?

[thambu19]

Originally Posted by steve99

I posted up some baseline Takeda scaling in the first post in this thread

From memory the guy was getting fuel trims of aprox 15% before i did some quick scaling for him got it down to about 5% .

MAF sensors dont measure the entire quantity of air passing through the intake. They take a sample and then this is used to estimate the total flow of air.

Hence if the size of the tube the maf sensor sits in changes, or even the flow of air past the maf due to its positioning in air flow stream or turbulent flow all effect what maf "sees".

Each intake type is different and just because to have to move the maf scaling up/down does not necessarily mean the intake is flowing more or less, it could just be the positioning of sensor has effected the sample "seen" by the maf sensor to estimate the total air flow.

The MAF reading is then used as an input to generate the "engine load" parameter which is used in many ECU tables to determine ignition timing/fueling and cam timing etc applied at different loads.

So if maf is off it can effect many engine parameters.

I agree. If the MAF is causing the engine to use a 15% positive fueling correction the engine will run as if it will bog down because it will be looking up a spark 15% higher which is usually more retarded. Worst would be at WOT where in OL the engine will receive 15% excess fueling for no good reason. I just did not understand that bump in the middle of the curve and I think @solidONE had a neat explanation as to why it is needed.

Edit: I think I was wrong with the assumption that the LTFT will make engine run rich in OL. The LTFT was merely correcting a lean condition in CL caused by under-reported voltage/maf so it basically brought the load evaluation back to square one. If that is the case then it wont make engine look up a wrong load and hence fueling/spark

[solidONE]

Originally Posted by thambu19

@solidONE
So if someone bolts on the Takeda intake without any MAF scaling does the LTFT go +ve or -ve and by how much overall?
I sort of understand the concept a but but perhaps the answer to the above question can make me understand better.

From the looks of the scale you posted, LTFT would go up without changes to the stock maf scale. Higher fuel trims will require the MAF scale values to go up, and vice versa.

The def file provide by Vishnu do not have the Load limits defined. You can download Wayno's def files in his thread and he has the load limit tables defined under the Mass Airflow folder. Have fun!