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Old 01-14-2010, 10:43 PM   #41
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I looked for a simplified linear equation.

It's this:

MAPRPM = MAP*RPM / 7000 / 100

voltage = 2.757 * MAPRPM + 2.154

The RMS error is 4.7%, but it's worst at low kPa and especially around idle.

Could you repost the equation I gave you?
Do you still have the raw data?
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Old 01-15-2010, 12:42 AM   #42
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Originally Posted by JasonC SBB View Post
Bad choice of words on my part - I should've said the injector PW's will suddenly drop for a given MAP/RPM combo when the EGR valve opens, because the exhaust gas will displace fresh air.

So if you open the EGR at say 3000 RPM, your map in theory should have a certain inj PW (and timing) at 2999 RPM, and a different PW (and timing) at 3001 RPM (you get the picture).

The other option is to gradually open the EGR valve from 2500 to 3000 RPM (e.g. 0% duty at 2500 and 100% at 3000). That way there's no step.
Oh I see, well the other side of that is, I don't think the MAP sensor would record a massive shift in MAP. The flow rate of the EGR should be pretty low. So while mass flow rate goes up, and fresh air mass fraction goes down, total fresh air mass probably stays pretty much the same.

I think we need to test this theory well because I could be wrong, but while I had the EGR hooked up, I never noticed a rich/lean spike when going over its activation range.
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Old 01-15-2010, 04:19 AM   #43
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Well in theory the EGR would have to displace a significant amount of air, because that's how it's supposed to work! The increase in throttle angle needed for cruise reduces pumping losses which improves MPG. (cooler peak combustion temps reduces NOx too).
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Old 01-15-2010, 10:22 AM   #44
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Quote:
Originally Posted by TravisR View Post
Does the computer get angry when the MAF is maxed out?
Only in the form of a MAF overflow code. Used to get that one randomly after driving hard with the Xede.

There is also an underflow code.
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Old 01-15-2010, 10:23 AM   #45
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Originally Posted by JasonC SBB View Post
Now are you suggesting that you offload the MAF-mimic to a simple uC circuit just like you did your O2-mimic?
That would actually be a really sweet solution. Especially if there were a final 'polished' solution with NB and MAF signal sims in one box. Doeeett!
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Old 01-15-2010, 11:13 AM   #46
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Quote:
Originally Posted by JasonC SBB View Post
I do.

I think you typo'ed but perhaps the voltage is very close to a linear funciton of MAP x RPM. (with clipping at 100 kPa)

Now are you suggesting that you offload the MAF-mimic to a simple uC circuit just like you did your O2-mimic?

i typod. 3000.

I wasn't suggesting to offload the maf mimic, but at that point you now need a bunch of inputs to that circuit. or two 2D outputs (RPM and MAP).

I never had an equation I dont think. I just have the map values.

oh wait, i just realized i made an equation in excel that handles the N/A discontinuity. the spreadsheet is attached. values are in voltages and need to be scaled appropriately into duty cycles or whatever.
Attached Files
File Type: xls mafdupe.xls (55.5 KB, 89 views)
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Old 08-25-2010, 12:40 PM   #47
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I'm thinking of building a uC board that will implement the MAF signal. Among other things, it will improve the factory ECU's idle control, and enable EGR if I wanted to.

For posterity's sake, the original curve fit equation I gave to Matt eons ago which fit data I collected on my TEC3 from the AFM is:

First divide MAP by 100, and call it MAPscaled, and RPM by 7000, and call it RPMscaled (this scales the coefficients to be easier to read, and may make it easier to code if your uC has integer math as opposed to true floating point):

1.6893
+ 1.6504 * RPMscaled
+ 0.90739 * MAPscaled
- 0.88739 * RPMscaled^2
- 0.21516 * MAPscaled^2
+ 1.4595 * RPMscaled*MAPscaled

It may be best to clip MAP to 100 kPa, (MAPscaled to 1) because the factory ECU isn't expecting > 100 kPa's worth of airflow at the various RPM's.
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Old 08-25-2010, 12:42 PM   #48
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Quote:
Originally Posted by JasonC SBB View Post
I looked for a simplified linear equation.

It's this:

MAPRPM = MAP*RPM / 7000 / 100

voltage = 2.757 * MAPRPM + 2.154

The RMS error is 4.7%, but it's worst at low kPa and especially around idle.
Around idle (in the region 750-1000 RPM, 25-40 kPa, the best simplified curve fit is

voltage = 6.123 * MAPRPM + 1.85
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Old 09-10-2010, 02:41 AM   #49
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If the intialization for a sensor passes with the out of the box no modifications Adaptronics hooked up, will it show readiness codes for an emissions test?
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Old 09-12-2010, 06:45 PM   #50
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I'm such a curve-fitting geek. This slightly simpler equation has <1% error vs the original:

1.746
+ 1.639 * RPMscaled
+ 0.6576 * MAPscaled
- 0.8774 * RPMscaled^2
+ 1.465 * RPMscaled*MAPscaled

And pls ignore the curve fits prior to my post #47, I typo'ed.

It takes my prototype 16 MHz Arduino board about 100 us to calculate the above equation, scaled into long integer math.
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Old 09-12-2010, 06:46 PM   #51
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Quote:
Originally Posted by Ben View Post
That would actually be a really sweet solution. Especially if there were a final 'polished' solution with NB and MAF signal sims in one box. Doeeett!
I now have a prototype Arduino Duemilanove board implementing 12-1 -> NB crank trigger signal conversion, as well as MAP+RPM -> MAF. Stay tuned. I just took it to the mountains and drove it 100 miles.
I had to exercise the C-code part of my brain that hadn't been exercised in >15 years!
Maybe we should get Reverant to convert the code from Arduino-C into generic (non Arduino) Atmel code. I can design the PCB layout and build a prototype.
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Old 09-13-2010, 03:02 AM   #52
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Send me the code and the schematics and I'll see what I can do.
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