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LE. I was wrong.
With a lot of help from people years ahead of me in terms of software, I was educated on how these 3 tables work and what they mean.
First let's define some stuff:
0) (zero because computers count from 0 ) There is only 1 kind of load. The value is on 16 bitsm then it gets corrected and turned into a float. That is what the ECU uses in all its tables. Say engine rpm vs engine load, well that's the load I mean. I shall call it from now on, simply, LOAD.
1) What ME logs as Calculated load... under OBD2 pid at 0X04 is an 8 bit truncated value of load and scaled to be from 0-255 to 0-100%.
2) What ME logs as Absolute load... under OBD2 pid at 0x43 is the full engine load you see in the tables. It is a 16 bit unsigned value, 0-65535.
3) Both "calculated load" and "absolute load" are calculated from the same variable the ECU works with(remember, the one above ! ^^^^^^). Absolute load is the entire variable and the only one used in the ECU tables. Calculated load is the most important part of it.. if you may.
4) "True" load is really how much load there is, with no one limiting it. If you'd run 5 times the athmospheric pressure and in an ideal fashion, then load would be 500%.
If "true" load is under the load limit...then true load = load and is used properly by the ecu. You always wanna be in this area!
How load is computed... the ecu does some math based on maf, rpm, VE, etc etc. It comes up with a percentage. Like 154% for example.
Then these 3 tables come into play. These 3 tables form a load limiter. Multiply the numbers in the 3 tables and you'll get a result like, say, 98.6%. This is our load limiter. Oops, our load is higher than the load limiter ? Then, our load is the load limit itself!This means that the load the ecu needs to use in an engine load-based table, it will use this capped value of load. Load = load limiter.
When the ecu uses the load limiter and not "true" load:
Less fuel will be injected(because, say you have 154% worth of air in the engine, but inject only 98.6% instead of 154% worth of fuel).
Ignition timing won't be adjusted properly for the "true load" we're getting. You may have set a timing for, say, 154% which is retarded compared to say, 98.6% which is much higher.
Any and all load-related tables will be capped at the load limiter.
Thus the question is... what does it mean when you see Calculated Load flatline at 100% on your logs? It means that the ecu has computed a load which is above its maximum load limiter. Thus, it reports the maximum digits as being all 1s -> 255 -> 100%.
Why is this so easy to spot, and why 100%... the answer lies in data representation. I wont nerd you with the details but you can math it out if you don't believe me. 8 bits truncated from 16 bits. MSB first representation.
What to do when chasing more power?
Max out the "calc load max" table... the name is wrong. It should be "Load limiter base value". Set it to 200 % in the areas where you expect to hit more load than stock.
Set IAT and BARO tables to 1.1 for starters. This will allow you to go to 200 * 1.1 * 1.1 = 242%(THIS is your load limiter) which should be plenty for what this engine can take.
Do your tuning and observe load, under the parameter "Absolute engine load". It should never reach 242%. Say, it reaches 170-180%. Then set the limiter to 200% and that's it.
You now have the ecu never reach the load limiter under normal conditons, but if your MAF acts up or anything else implausible happens, then the ECU won't go crazy with it.
Why not set the load limiter to 42342% if we can?
It is a load limiter in the sense that it caps fuel injection and timing and so on(recall, every table where engine load is used). If you let it go crazy the ECU can max out the injectors at any time the MAF tells it to... such as a break in the wiring, bad MAF, crazy scaling etc.
There, the more you know.
Last edited by ciprianrx8; 11-12-2023 at 12:57 PM.
Reason: new knowledge
Just noticed this. Glad you came back and sorted it out as you had me 2nd guessing myself for a while. I always increase the Max calc load on modified N/A rx8 by 15% with the thought that it is actually useful if the maf sensor stops functioning. With FI tunes I set the table to 200% but leave values below 2000rpm at a much lower setting as no boost is typically made there.
This has only become totally clear to me recently.
.
The Baro compensation map is only used by the ECU in this calculation for 'max. calculated load' .
I am in the learning process and oh boy the learning curve is steep
The first thing to clarify the barometric pressure sensor is used in combination with an air temperature sensor to correct the MAF reading.
ECU needs to know the input air temperature and local atmospheric air pressure to ETA mass of air.
Also, note that there is a curve and they are not linear, not sure why are linear on ME screenshot?
The logs on dyno/ local/unchanged altitude would not show any changes, however, changing those values would affect the engine behavior in all ranges and most importantly destroy the calibration of MAF on a trip/ change altitude.
That is you saying that, not you actually testing it ..... I would have thought so too. Which is why I actually tested it before stating the above.
I did not say that it is written in all books. That is how the EFI designed since '90s.
ECU even before starting the engine would measure the baro sensor and use a calibration table to read/interpret the MAF reading which is a voltage.
MAF sensor is dumb and can not tell how many grams/pound of air is coming to the engine, it only measures the flow of the air, and can not count how actual grams/ mol are on that air unless looking to other inputs to ETA local air density. Even the molecular weight of air would change corresponding to air humidity, a deep rabbit hole...
As I said you cannot measure this on dyno or log in with convention methods. However, I can produce isolated tests if you want ?
I did not say that it is written in all books. That is how the EFI designed since '90s.
ECU even before starting the engine would measure the baro sensor and use a calibration table to read/interpret the MAF reading which is a voltage.
MAF sensor is dumb and can not tell how many grams/pound of air is coming to the engine, it only measures the flow of the air, and can not count how actual grams/ mol are on that air unless looking to other inputs to ETA local air density. Even the molecular weight of air would change corresponding to air humidity, a deep rabbit hole...
As I said you cannot measure this on dyno or log in with convention methods. However, I can produce isolated tests if you want ?
You seem to be saying that what I said (ten years ago) after doing multiple tests to come to that conclusion... is wrong. What I'm saying is ..... don't just say it ...........prove it!
You seem to be saying that what I said (ten years ago) after doing multiple tests to come to that conclusion... is wrong. What I'm saying is ..... don't just say it ...........prove it!
No worries I will
to clarify one last time, you want to see the correlation between the other sensors namely baro and temp on the MAF reading?
No worries I will
to clarify one last time, you want to see the correlation between the other sensors namely baro and temp on the MAF reading?
Yes, prove that the IAT sensor and baro sensor actually have an effect on the maf reading. Not through what Joe bloggs said in some book .............. by actually testing it!
Here is your " proof " . Sorry for the delay, working full time as a dentist doesn't leave me lots of time for hobbies.
Baro sensor has hole inside of plug and I am not willing to destroy sensor for prove of earth is not flat, so I can not hold vacuum but still it is visible how linear is the changes on maf reading when I pull vacuum. Engine is not cold and rpm is stable until I pull cavum and maf reading goes all over the place where the engine wants to stall.
Had a bit of an epiphany this evening.
The baro sensor does alter the maf sensor values .................. however the chart I originally referenced (and tested) in post 1 of this thread ...does not. That chart is the 'baro calculated load compensation map' and has nothing to do with the actual sensor readings.
So, oy original suggestion to use this chart to raise the calculated load cieling and thus allow higher loads than 200% ............. is still valid!
The first thing to clarify the barometric pressure sensor is used in combination with an air temperature sensor to correct the MAF reading.
.
Looks like you were correct about the baro sensor but wrong about the IAT sensor :
First 5 seconds : steady air sensor temp, air flowing through maf tube.
5-19 seconds : air temp sensor heating up to it's max. (in a separate airstream) , air flowing through maf tube
19 seconds on : air temp sensor cooling down, no air flowing through maf tube
Nice work. I'll take that on the chin and correct my error re the baro sensor. Are you doing something similar with the temp sensor?
No worries mate. I am not planning to do any changes on other sensors or any sensor per se. Why should I use the back door when I have full access to the front door ? it's worth fooling around if you don't have access to tables to do so " pigback" as I believe many other turbo kits do. What I found is that the out of the box versatune already did changes to tables as seen on screenshots. interesting one the "unknown table"
This is an OEM table inside N3ZHEC calib. which states that depending on baro pressure, the reading from the wideband o2 is corrected. This comes from a guy much smarter than me, on par or above the guy which made mazdaedit. This is not specified anywhere else so f*** knows what else is tied to whatever else and no one found out yet.
Last edited by ciprianrx8; 04-19-2024 at 04:41 AM.
05-26-2023, 04:04 AM
) There is only 1 kind of load. The value is on 16 bitsm then it gets corrected and turned into a float. That is what the ECU uses in all its tables. Say engine rpm vs engine load, well that's the load I mean. I shall call it from now on, simply, LOAD.
