Kelivin kPa

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Kelivin kPa

Postby Charlescrown » Thu Jan 31, 2019 4:05 pm

Just looking through a 411 bin file and have a question relating to the main ve table. What is a Kelivin/kPa? Can I assume it's air pressure?

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Re: Kelivin kPa

Postby vlad01 » Thu Jan 31, 2019 4:22 pm

Probably ideal gas law scalar. Absolute temp vs absolute pressure.
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Re: Kelivin kPa

Postby delcowizzid » Thu Jan 31, 2019 7:45 pm

Kelvin is temperature
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Re: Kelivin kPa

Postby Charlescrown » Fri Feb 01, 2019 6:25 am

That was my first thought till I did a google and noticed it was not kelvin but kelivin. I know the scaler is what someone wrote to represent a scale but I have never heard of kelivin. It sure looks like air pressure starting at 0.08 and ending up at 1.2 so I assume that's bar. The same scaling (not labeled) is used on the spark table and both against rpm.

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Re: Kelivin kPa

Postby vlad01 » Fri Feb 01, 2019 10:59 am

It would be a scalar for the amount of temp increase with air pressure. As pressure increases the temp goes up automatically and vise versa. Sounds to me a scalar for temp offset depending on air pressure. It should be part of ideal gas law calculations looking at it.
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Re: Kelivin kPa

Postby Charlescrown » Fri Feb 01, 2019 2:02 pm

Yes I understand what Kelvin is and pressure and temperature but kelivin is unheard of for anything. Maybe it's an error and meant to be kelvin but to put it in a part of the VE table and Ignition map.
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Re: Kelivin kPa

Postby vlad01 » Fri Feb 01, 2019 3:15 pm

looks to do what I thought. Would be just a typo
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Re: Kelivin kPa

Postby NSFW » Fri Feb 01, 2019 4:37 pm

I agree, it's a typo.

Coincidentally I am just (barely) far enough into disassembling my car's OS to be able to find the code for this stuff. :)

At address 456DE there's a function that gets called to look up PID 000B, manifold absolute pressure.
That function reads a value from address FFADB8 in RAM, so I labeled that value Pid_000B_ManifoldAbsolutePressure.
That gets copied to address FFADB6, which in turn gets copied to address FFADB4, which I renamed to VE_MapAxisInput (you'll see why).
It divides the value by 51 before returning it, so I guess the units are 51ths of a kPa, but I wouldn't stake my life on that claim.

There's a function at 456D2 that gets PID 000C, engine speed in RPM.
That function reads from FFA0C0 and divides it by 5, so I labeled that Pid_000C_EngineSpeedIn5xRpm.

The code that uses the VE table reads the Pid_000C_EngineSpeedInRpm and ensures it's between 400 and 8192.
Then it reads the VE_MapAxisInput value and ensures it's at least 15kpa, but it doesn't appear to enforce a max value.
Then it passes those two values and the address of the VE table to a function that does the actual lookup.

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