DTN

This is the only thing I could find on the entire HMA Service site. I recreated this formula from the TSB.



It's listed under this TSB http://hmaservice.com/local_viewer/default...p;title_num=331

What sensors go into calculating load?

Albuquerquefx

Ah, something I can help with laugh.gif This was my forte back in the day...

There's an immediate problem with the formula given: not many cars have both MAF (air density) and MAP (air pressure) sensors; the RD's are all equipped with MAF sensors. Second, "peak" air flow is a bit of a misnomer; peak according to what? If you define "peak" as the total volumetric flow of the stock engine at maximum possible load, then when someone slaps on a cold air intake, a new set of cams, and whatever else, the computer should simply give up!

Let's knock out the obvious bits:

"Peak airflow" on a stock MAF-equipped computer-controlled car is entirely limited by the ECU lookup tables and the capabilities of the MAF sensor. We don't exactly know where the stock ECU or MAFS craps their respective pants, but we can make some educated guesses...

"Current airflow" on a stock MAF-equipped computer-controlled car is based on (obviously) the MAFS and the IAT. The MAFS determines air mass by how quickly a heated element is cooled, but you also need a temperature to compare to. Colder yet lower-density air may cool the MAFS element quickly, but perhaps not as fast as slightly warmer and yet higher-density air.

Lastly, obvious answer is obvious: "Atmospheric pressure" and "barometric pressure" are impossible on a car not equipped with manifold or barometric pressure sensors.

So, what does this leave us with in terms of that equation? In reality, the only "unknown" component of calculated load is the quantity of air that is filling the cylinders. The computer already knows RPM, temperature, throttle position, coolant temps, blah-dee-blah. Thus, the only two sensors that calculate load would be the MAF and IAT sensors.

DTN

^^ thank you. From what you said I was able to get more information to fill in the blanks on this equation. I found a chart explaining effects of air temp on pressure and was able to find the value of sea level pressure. The TSB stated that the airflow is 100 gallons per second max. So that leaves the only variable unknown as curent airflow, which is about 3 gallons per second at idle.

Here's the modified chart.



to get Celsius, ((Fahrenheit degrees - 32) * 5) / 9
so an average day = 70F or 21.1C
20C is closest value on the chart
chart says: 20C = 1.204 kg/m³
convert to lb_m/ft^₃:1.204 /16.02 = .0752
airflow at idle = 3gpm, max airflow = 100 gpm
to get airflow ratio: 3gpm / 100gpm = .03
sea level = .074887lb_m/ft³, air pressure = .0752lb_m/ft³
to get pressure ratio .074887lb_m/ft³ / .0753lb_m/ft³ = .9958
so airflow ratio =.03 and pressure ratio = .9958
so to get total load on the engine we multiply the ariflow ratio and the pressure ratio and multiply by 100 to get percent
load= pressure ratio times airflow ratio = .03 * .9958 * 100 = 2.9874% load at idle

wow. it works.

Albuquerquefx

LOL, I'm not gonna double-check all your math, but that doesn't sound unreasonable.

Glad I could help smile.gif

DTN

Here's a snapshot of my car driving in 3rd gear, and about 6200 RPM.


According to the calculations laid out by Hyundai, my car was actually running 118% maximum load?

I'm guessing that Hyundai would have had to modified the ECU's software since the TSB was written in 1996 . Maximum airflow must be around 115-120 which would put my readings right on the line of 100%.

DTN

I found this while searching the internet http://www.racecarbook.com/pdfs/36airdens.pdf

<div class='quotetop'>QUOTE </div><div class='quotemain'>CALCULATION EXAMPLE -- PRESSURE & TEMPERATURE EFFECT:
(1) Assume a local barometer reading at Norwalk is 30.05
(2) Determine an uncorrected value. Either find that value from a source that has uncorrected
barometric pressure in inches of mercury or convert the value from a correction
table or chart. The correction for 700 feet elevation is approximately - 0.7 inches or mercury.
The uncorrected value is: 30.05 - 0.7 = 29.35
(3) Assume a temperature of 90 deg. F
(4) Convert to absolute: 90 deg. F + 459.67 = 549.67 deg. Absolute
(5) Air density % = 1,736.86 x 29.35 / 549.67 = 92.7%</div>

This value could be used to replace the 2nd fraction with barometeric pressure at the top by using the uncorrected value. This eliminates the table and the X 100.

It can be simplified because the car always assumes sea level
Air density % = 52192.643 / (459.67 + temp in F)

Our IAC can correct for

<div class='quotetop'>QUOTE </div><div class='quotemain'>temperature - Voltage
0 (32)3.3-3.7 V
20 (68)2.4-2.8 V
40 (104)1.6-2.0 V
80 (176)0.5-0.9 V</div>


I'd say it would be safe to say my car's intake temp should be lower then 136F on a really hot day. So It would be safe to increase the resistance accordingly. So at 50GPM, an average take off, on a 70F day, your car would read 49.24% load. However, if the IAT was tricked to think it was 110F, it would read, 45% load....

I am so going to get slammed for this calculation........

So.... um..... Ebay modchip inline with the IAT, reducing the voltage, would lean out the fuel ratio, thus yeilding more power and better fuel economy for our cars which run too rich?

REDZMAN

1. Get a spoon.
2. Weigh it.
3. Shoot your load in said spoon.
4. Weigh it.
5. Subtract the weight of empty spoon from weight of load filled spoon.

Load calculated.

load filled spoon weight - empty spoon weight = Load Calculated.

...

Sorry.

WTF would make you think I'd know any of this DTN? LOL I'm anti math.

tanc

DTN, simply leave it alone. You are not going to re-engineer our ECU's. If you really want to play with stuff, go get a standalone and stop thinking of loading resistor boxes. What ever gain you get, it will not be anything significant to justify what work you put into it. Go get a standalone if you want to play with real values.

DTN

A wideband like this:
http://www.rdtiburon.com/index.php?showtop...256&hl=load

and a potentiometer like this:


can potentially answer any a/f problems in low boost applications.

Stocker

So . . . you concluded in April last year that you wanted to reduce the IAT voltage, so you put a potentiometer on the MAFS, completely unbalancing the wheatstone bridge and possibly frying your ECM. Right.

Dude, if you want to drop a half a volt, just slap a diode into the IAT signal line and call it a job. Tinkering as shown above with the MAFS lines seems a very bad idea.