This has only become totally clear to me recently.
I know there are a few people out there that shared my struggle to understand this ,so thought it worthy of a new thread to dispel some of the misinformation that has surrounded this subject.

So
What does the 'Maximum calculated load' map do ?
Nothing mysterious at all - contrary to suggestions by a well known tuner to portray it as such .
Basically it forms a ceiling for the amount of fuel that can be injected ,mostly (but not only) under wide open throttle situations .
If the max set value is 100% and actual load was 110% the fuel injected will be the same as it would have been at 100% . So - engine runs 10% leaner.
End of story !

Why does it do this ?
This , I am less sure of, but my best guess is that it is used to prevent gross over fueling in situations where there is some fault in the system . EG Maf faulty , maf tube issues etc.
Mazda knew how much air their engine will ingest under all circumstances so it is easy to make sure it doesn't get more fuel than it needs.

Why is this an issue for us ?
If the engine is modified substantially (eg, porting or FI) all of a sudden this max. calc load map limits our ability to add the correct amount of fuel unless we alter it .
The issue for turboed engines has been when we reach the maximum limit of the Max calc load map - which is 200 % . This has limited tuning to around 12-13 psi above 6500rpm.
Edited:
How can we around this?
Multiply all values on the 'baro calculated load compensation' map by whatever value you need to. IE if you want 220% multiply by 1.1 200x1.1 = 220

 

I don't remember seeing that map in my Access Tuner. I'm at work so I can't look at it to confirm. I'm assuming this is a ME only option?

 

nope - you have both maps shown above ....

 

we have the maps, it just doesn't work this way with the Cobb ATR program, it appears to be capped at 200% regardless


edit: while I could edit values in ATR, I couldn't actually test the high loads and therefore I was wrong in my assessment of the situation.



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Good stuff Brettus thanks.

Sooooo ummm

On a boosted application are suggesting that you flatten the baro table?

If so then flatten it with the multiplier you would like for Max Calc Load?
For example if you were happy with 200% calc load you would flatten the baro table to 1 or 1.5 if you wanted 300% load?

To me it would seem like you wouldn't want to mess with the Baro table to much after tuning.
(Set it once and leave it)
This is more like a table you would setup before you began WOT tuning, yes?

FWIW my current tune has the Baro table flattened at 1

 

I don't see why it would be any different for ME vs ATR .

I have tested the above scenario . ie setting the baro table to 1.5 and it had zero effect on the reported calc load or the actual air fuel ratios . That combined with the info i gleened from slashs' thread lead me to the conclusion that the baro table only effects max. calc load and therefore can be manipulated to give you any max calc load you want .
I also researched 'hot wire maf' and there was conflicting information as to whether air temp or baro pressure were needed to determine air mass . Most evidence i found suggested that they weren't.


with any luck Slash may be able to test ATR to confirm .

 

Exactly


I think the whole reason this subject has taken so long to unravel is that the thinking (promoted by you know who) was that Max calc load was somehow important to tuning . My belief now is that it isn't at all . The reason for the table I came up with above is only a guess but .. it's plausible.
If you accept that it isn't important then all you have to do is make sure it doesn't interfere with the tune .
BTW I have always set max calc load to 200 flat and have never seen any issues in the rpm ranges that go nowhere near that load .

 

edit: while I could edit values in ATR, I couldn't actually test the high loads and therefore I was wrong in my assessment of the situation.



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Can you elaborate on what you actually did ,what you measured, and what results you got ?

 

When I was testing this idea of increasing the baro and IAT tables to increase the max calc load, I found that it just changed the reported value, with all else being the same.

What seem to happen is the system determines its calc load then go to the AIT see the temp then do the multiply. Then again for baro. So by changing the tables, it basically just changes the reported calc load erroroniosly.

 

*I think* the difference is modifying both IAT and Baro vs just Baro alone. I would like to log this.

 

would be nice if this did work on the AP. Looking forward to Team's response and Slash's testing.

 

suggest you do the same test I did and set Baro to 1.5 .

You should be able to see if it does anything at idle . If idle and cruising is not affected then WOT wont be either .

Also : there is more than 1 load parameter you can monitor . Try monitoring all of them .
The key thing is : Does AFR change ? If not (at a potential 50% extra load) , then you know it is having no effect .

 

I will try to do this tomorrow

 

So I just logged this, same tune back to back. One with stock Baro and one with Baro comp set at 1.5 across the board. Calc load was pretty much the same between the two. It was a little off, talking 187.7 vs 190.5, but not by 1.5X. So it seems the Baro table is not actually used in modifying the load? This is interesting. But my question at this point is, ok, we can set the Baro artificially high without affecting reported load, but how do we know it will allow us to play in areas above 200%? We tried this back in April, but by modifying both the Baro AND IAT tables and we found that the Calc Load would go up *mostly* proportionate to whatever values we plugged into BOTH of those tables. For instance, at one point we had both the Baro and IAT set at 1.03 for all values originally below 1. Calc load was reported at 189.73. Then we raised Baro and IAT to 1.05 and in that log load was reported at 200.7. So if you multiply the load by 1.02 (the difference increase between 1.03 and 1.05) then you get:

189.73 x 1.02 x 1.02 = 197.4

Intake temp was also down by 3.6F degrees in the second log. Other factors are probably contributing to the difference not being exactly spot on between runs as per the calculation. Anyone with a better understanding of how these tables inter-operate please feel free to jump in and make sense or call nonsense

As we continued to tweak with this we were seeing calc load in the 210-220 range, albeit artificial, and fueling/timing was where we wanted, so it seems it is possible that the ECU can deal with it. The bottom line is that modifying both Baro and IAT yielded noticeable results, while modifying Baro alone did not seem to impact the numbers. Perhaps it was only the IAT table that was artificially increasing our reported load and other factors were throwing it off far enough that it appeared Baro was part of the equation. Guess it is time to turn up the boost and experiment

 

/\ I strongly suspect this is what you were seeing :

Actual load (with elevated maf) was lets say 220% , but max calc load was limited to 200 x whatever the compensation would have been .
So lets say you saw 200% reported on one setting then you increased baro comp to 1.05 . Next run you would see 210% reported . But increase baro to 1.5 and now your ceiling is way above actual so you see the correct figure of 220% reported .


As an aside : I believe I know why mazda went to so much trouble to make the 'max calc load map' - It is to stop over fueling as mentioned in the OP but the reason for that is to protect a very expensive item that could cost them a lot of warranty if it failed ...................................... the Cat !

 

Ahah, so in essence it was revealing what was previously hidden.

 

Exactly . It was giving you the impression that the baro table was affecting calc. load when it actually wasn't .

 

So this actually may give a new lease on life for the usefulness of the Cobb for me... Aside from reaching the load ceiling my only other big issue was not being able to log an external wideband. At this point though I am caring less about actual AFR. I just look at the VD graphs. If power is increasing I continue in that direction. If it starts to fall off I just go the other way. As long as I know I am staying out of danger the actual specific AFR value is not so important.

 

Excellent . And thanks for testing this and reporting your results BTW.

It would be very handy but not essential . So long as you don't go up in too much of a leap each time you increase the boost , you should be fine.

 

No problem, this is cool stuff and I am happy to participate. Appreciate your work on this!

 

Cheers
BTW : I suspect that the temp comp. table doesn't affect reported calc. load either and works exactly as the Baro table does .
I have not bothered to test this.

 

^ - If the weather holds I will try to log this tomorrow...

 

I loaded up a file with the Baro and IAT both flat at 1.5 and max Calc Load flat at 2. It started pouring down rain, so no high speed logs, but so far normal driving all looks normal. Fueling and timing are right and Calc load is as expected. Hopefully it will be dry tomorrow...

 

Maybe I gave up too soon.
Still seems odd though I think its just changing the calc load reported