03whitegsr

iTrader: (8)

You are disregarding the fact that your baro reading drops as you are at WOT because of Bernoulli's law. It's not uncommon to see baro drop 5-10kPa on a pull, which is a signifigant change (5%-10% density change).

D-VO

iTrader: (1)

Lower pressure = higher air speed then and lower air temps right?

D-VO

iTrader: (1)

Doesn't air density and air pressure have a direct relation? If the air pressure goes down 7% at 2000ft won't the density do the same? That's why i fugured a 7% difference in the AFR's at a 2000ft elevation once the airlfow Hz table values are correct. I'll give up if you say I'm wrong.

03whitegsr

iTrader: (8)

It has to do with dynamic air pressure and energy conservation. Air speed causes a dynamic pressure to develope, the higher the velocity, the higher the dynamic pressure.

Your air source (ambient air) has a total pressure of 14.7 PSIA (at sea level). As you acclerate the air up to the inlet velocity at the meter, static pressure drops and dynamic pressure increase, but total pressure remains constant (neglecting pressure losses).

The pressure sensor in the MAF is a static pressure transducer. Thus, as the air flows into the meter, the static pressure drops with increasing airflow rates. There should be a baro compensation table that deals with this directly as it is relevant to all MAF frequencies and not just 200Hz and below. This should correspond to a table that is a correction to the MAF calculation based on MAF freqeuncy that will likely be non-linear.

The theorectical equation is Dynamic Pressure = 1/2 * air density * (air velocity)^2

It could be built into the MAF scaling though?

I think this table mentioned above is only meant for light loads and is probably a correction to improve part throttle driveability. I think the main table that Mitsubishi meant for IAT correction is the table mentioned in post #58 and #68 by Mattjin. I could be wrong, but it looks like what I would expect for IAT correction once you multiply them together. Dissassembly would verify the operation of these two maps, but I have no skills on that.

mrfred

iTrader: (50)

I finally took a look at the code that calls those tables. They don't play a role in WOT fuelling. Without spending a day looking at the code, my assessment is that the code that goes with these tables is either some sort of limp home code for a dead MAF or are startup related.

03whitegsr

iTrader: (8)

That sucks.

There has got to be some enrichement for IAT some where though and it just doesn't seem right to mix baro and IAT together in one table then have it zero'd out at higher loads from the factory.

mrfred

iTrader: (50)

The values from that table will carry to high loads. The last row of values will be used for all MAF frequencies ≥ 201 Hz.

D-VO

iTrader: (1)

Hey guys. How about changing the verticle cells? Say to value's of 0,300,600, ....... , 2400. With factors of 300, it ends up taking up all 9 cells. The factory MAF sensor reads up to 2500Hz right? Also, the fraction values on the table are exactly the same anyway except for the cells 0 and 25 (which you never see unless your starting up). So, it would look something like this:

What do you guys think?

mrfred

iTrader: (50)

There's nothing technically wrong with doing that, but is it needed? The MAF Scaling table should handle what you've done with the example table in your post.

D-VO

iTrader: (1)

Well, I figured I can get much more control over the AFR's for all MAF readings at all MAF temps. I found a thread a while ago about re-scaling the MAF scaling but it didn't make sense to me. Actually is still doesn't. Does MAF scaling help with air temp compensation as well or just how it reads?

honki24

iTrader: (23)

Very good point. I haven't been logging Baro. Suppose I'll need to.

Did some more math though.

*Perhaps a table makes this more clear than equations do.

80F and 15psia =~.149 lb/ft^3

Looking at logs from my pulls and assuming worst case as you've said (10kPa drop):
air temps increasing from 80F up to 110F =~21% density decrease
air pressure decreasing by 10kPa (1.5psi) =~5% density decrease

So over the course of a hot pull I can expect the ECU to see ~26% decrease in air density with temperature having 81% influence.

As you can see, again, I prove that baro is much less significant. It is 4 times less significant. That extra 5% loss in density is far too detailed for this very low-res table to even attempt to compensate for.

03whitegsr

iTrader: (8)

Yeah, I understand that. Just typically, when you see a map that tapers off to 1.0, it typically means it a correction for a non-typical running condition. Like when coolant temp enrichment tapers off to 1.0 as it approaches the 70C range. It's meant to turn off the correction at some point.

Maybe it is the only IAT correction, but typically your AFRs should vary with intake temps independantly from baro/MAP.

03whitegsr

iTrader: (8)

honki,
Maybe it wouldn't help as much on a road course, but when using an insulated cold air box that sources air from the front of the car, I was always able to keep IAT within a few degrees of ambient. Maybe improving your intake track to source air from a cold place would fix your varying AFRs and provide a boost in performance.

I agree that temp change poses a more significant role absolutely, but I've been able to keep intake temps well under control in my car where baro is a significant source of density change, relative to temperature changes.

honki24

iTrader: (23)

Yeah, I hear you. I really was just trying to use the track as an example. What I see as more of an issue is when I tune my car at 32F and then go race a couple months later at 110F. My AFR is not where I want it. It's through the floor. I suppose I should have stated it this way:

I live at sea level. I race at ~650' max.
I may tune at 50F. I may race at 110F.

The difference between when I tune and when I race, considering the above, would be this:

11% decrease in air density due to temp rise.
3% decrease in air density due to static pressure drop.

So what I'm saying is that when temperature is more than 3X more important than baro I would be inclined to ignore baro changes all together. I find it doubtful that many face the situation where their air temp is the same from day to day (unless you're in san fransico) and then the baro change due to intake velocity is more of a concern. I'd be willing to bet that the ECU should be nearly well tuned for that situation. Surely they've taken that into account somewhere. Perhaps the ECU even ignores baro changes in this calc when load exceeds "x" or something like that. Then the x-axis would be merely a function of temp.

I do agree with you though that I find it odd that we can't uncover a dedicated IAT only fuel trim table. There's gotta be one.

l2r99gst

iTrader: (2)

Well, I don't know all of the details as well as mrfred or jcsbanks who have or are going through the ECU code, but the ECU calculates the mass airflow and then the injector pulsewidth is calculated based on that. The mass airflow incorporates temperature and baro.

So, I don't know if there are specific tables that do exactly what you are looking for, but temperature is accounted for in the mass calculations. There seems to be additional trims for timing for excessive conditions, where timing may be pulled a few degrees for IAT (tables already found and posted), for example.