AFR gets leaner with higher IAT
05-13-2007, 10:27 PM
#1
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AFR gets leaner with higher IAT
My AFRs get substantially leaner as IAT goes up. For example, I can go out for a drive do a bunch of tuning, think I have things dialed in. Then I park the car for like an hour, IAT goes from about 80 up to about 120, and CLT goes from about 205 down to 175 (not sure my sensor is calibrated properly). Then I restart the car and suddenly my idle and low-speed (10-15mph) AFRs are really lean until the IAT comes down again.
The only two things I can think of that would be affecting it are IAT-related timing (because timing can affect AFR), and maybe an incorrect Req Fuel that is causing the ECU to make too large of a pulse width change for a given IAT change. My Req Fuel is 13.0, and I'm using 2000 injectors (240cc according to one of the FAQs here, haven't verified). Bigger injector = smaller Req Fuel. Smaller Injector = larger pulse width change to achieve a given fuel delivery change, right?
Any ideas?
-Mike
The only two things I can think of that would be affecting it are IAT-related timing (because timing can affect AFR), and maybe an incorrect Req Fuel that is causing the ECU to make too large of a pulse width change for a given IAT change. My Req Fuel is 13.0, and I'm using 2000 injectors (240cc according to one of the FAQs here, haven't verified). Bigger injector = smaller Req Fuel. Smaller Injector = larger pulse width change to achieve a given fuel delivery change, right?
Any ideas?
-Mike
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05-14-2007, 12:02 AM
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Where is your IAT located? Sounds like it is heatsoaking. If your sensor is reading a higher temp than is actually being ingested, you will run lean. Hot air is less dense, so less fuel is required.
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05-14-2007, 12:10 AM
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There aren't any IAT-based fuel corrections on the megasquirt, are there? Only the spark adjustments?
-Mike
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05-14-2007, 12:43 AM
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Lex was talking about this in Reverant's "Occasional rough idle" thread. In MS2 I can change IAT based enrichment/enleanment. I'm pretty sure you can do this in MS-SnE, too. I added 1% at 100 degrees, 7% at 130 and 12% at 160. Those numbers are crude and could stand some tuning, though, and I haven't seen intake temps higher than 120 so they're just a guess beyond that.
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05-14-2007, 04:16 AM
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I found the IAT adjustments, though. They're buried deep under "Coolant-Related Air Density". Then you hit settings "Coolant-Related Air Density", change "Air Density Correction" to "Corrected", and then change "Correction Based on" to IAT corrected.
I'll give that a whirl at some point.
Is it normal to have VEs up around 115 at high load and high RPM at about 12.5:1?
-Mike
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05-14-2007, 07:15 AM
#9
yes it is you have a turbo after all 200% would not be impossible at some point. Trust me if the sensor is heat soaking then it will keep you lean on inittial start up as you wont have much compensation in that coolant range there is adjustment all the way up to 74 degrees celcius for that.
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05-14-2007, 12:02 PM
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yes it is you have a turbo after all 200% would not be impossible at some point. Trust me if the sensor is heat soaking then it will keep you lean on inittial start up as you wont have much compensation in that coolant range there is adjustment all the way up to 74 degrees celcius for that.
Haven't turbo'd yet.-Mike
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06-19-2007, 04:53 AM
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I finally got my 440cc injectors in, and have the car running again, but I still see this problem where the AFR leans as IAT goes up, and I also need about 117 VE to get about 13.0:1, which seems way to high for an NA motor.
Can anyone share all their misc .inc files? Also, what's the difference between airdenfactor.inc and matfactor.inc?
-Mike
Can anyone share all their misc .inc files? Also, what's the difference between airdenfactor.inc and matfactor.inc?
-Mike
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06-19-2007, 07:48 AM
#13
dude you should be way richer than 13-1 what is your DC? I would recalibrate my 02 sensor and then try my afr table. 
GL Just becouse you hit 117 VE doesnt mean you are overcompensating if the DC and everything else is normal then you migth just be making some nice power. try theses AF's in autotune and see how they work for ya.
GL Just becouse you hit 117 VE doesnt mean you are overcompensating if the DC and everything else is normal then you migth just be making some nice power. try theses AF's in autotune and see how they work for ya.
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06-19-2007, 08:31 AM
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Jim
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06-19-2007, 12:21 PM
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I'm running a GM open element sensor.
My airdenfactor.inc looks like this:
Which column is the percentage I'd want to change?
-Mike
My airdenfactor.inc looks like this:
Code:
; Generated using EasyTherm4.exe, ; ; GM AIT ; ; File generated for use with stock 2490 ohm resistor at R4 ; ; Steinhart-Hart coefficients: A= 1.625488E-03 B=1.953101E-04 C= 3.009536E-07 ; ; Input Data: Temp, degF Resistance ; 1.1369377661552E-14 25000 ; 100 1800 ; 210 185 ; AIRDENFACTOR: ; ADC Temp, degF DB 100T ; 0 Sensor Failure - 100% applied DB 61T ; 1 407.84 DB 65T ; 2 352.81 DB 67T ; 3 323.23 ... DB 98T ; 136 80.82 DB 98T ; 137 80.17 DB 98T ; 138 79.53 DB 98T ; 139 78.88 DB 98T ; 140 78.24 DB 98T ; 141 77.59 DB 98T ; 142 76.95 DB 99T ; 143 76.30 DB 99T ; 144 75.66 DB 99T ; 145 75.01 DB 99T ; 146 74.36 ...
-Mike
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06-19-2007, 01:13 PM
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The second column, the one that says 100T, 99T, 98T. That number is the actual percentage of the time to squirt. Ie:
For 73.36 degrees F, squirt 99% of the calculated pulse width.
For 323.23 degrees F, squirt 67% of the calculated pulse width.
To find item your ideal temperature, start a cold datalog and let the car warm up. Watch the AFR as the car warms up. When the AFR starts to lean out, write down the temperature. Let the car idle until the IAT rises no more - ie its fully heatsoaked. Give it some revs if you feel you need to change more areas. Once you have the datalog, open it up and notice at say, every 10degF increments how much off is the AFR. Calculate how much more you need to open up the injectors in % (dont' forget the 1ms opening time) and note the numbers down. Open up airdenfactor.inc, and for each 10degF increment, add the percentage to the second column, taking care NOT to the delete the capital T character. Once you are ready, recompile the code (run 'compile.bat') and you will end up with a file inside the "src" directory called "msns-extra.s19". Copy it to the parent folder (there will already be one there, overwrite it) and download the newly created firmware to your Megasquirt (connect the laptop to your MS and run "download-firmware.bat").
You may need to fine-tune the figures a second time using the same method, but you should be pretty close the first time around. Hope that helps.
Jim
For 73.36 degrees F, squirt 99% of the calculated pulse width.
For 323.23 degrees F, squirt 67% of the calculated pulse width.
To find item your ideal temperature, start a cold datalog and let the car warm up. Watch the AFR as the car warms up. When the AFR starts to lean out, write down the temperature. Let the car idle until the IAT rises no more - ie its fully heatsoaked. Give it some revs if you feel you need to change more areas. Once you have the datalog, open it up and notice at say, every 10degF increments how much off is the AFR. Calculate how much more you need to open up the injectors in % (dont' forget the 1ms opening time) and note the numbers down. Open up airdenfactor.inc, and for each 10degF increment, add the percentage to the second column, taking care NOT to the delete the capital T character. Once you are ready, recompile the code (run 'compile.bat') and you will end up with a file inside the "src" directory called "msns-extra.s19". Copy it to the parent folder (there will already be one there, overwrite it) and download the newly created firmware to your Megasquirt (connect the laptop to your MS and run "download-firmware.bat").
You may need to fine-tune the figures a second time using the same method, but you should be pretty close the first time around. Hope that helps.
Jim
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06-19-2007, 02:03 PM
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Thanks for the detailed explanation. You answered a bunch of questions I hadn't asked yet. Should I turn off warmup enrichment while the car warms up for this test?
I think I'll upgrade to 29v at the same time, since I don't have the source for 29t (I just got the .msq).
Do you realistically expect this to bring my high load high RPM cells down to something more reasonable? I looked at your .msq (don't remember where I got it), and your highest VEs are in the low 90s, which makes more sense for an NA motor.
-Mike
Should I turn off warmup enrichment while the car warms up for this test?I think I'll upgrade to 29v at the same time, since I don't have the source for 29t (I just got the .msq).
Do you realistically expect this to bring my high load high RPM cells down to something more reasonable? I looked at your .msq (don't remember where I got it), and your highest VEs are in the low 90s, which makes more sense for an NA motor.
-Mike
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06-19-2007, 04:49 PM
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1) Don't turn off warmup enrichments.
2) Yes, airdenfactor.inc affects the entire RPM range so it should bring them down. Mine (VE) reaches 95% on the max torque cell.
Jim
2) Yes, airdenfactor.inc affects the entire RPM range so it should bring them down. Mine (VE) reaches 95% on the max torque cell.
Jim
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06-21-2007, 04:50 PM
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Reverant, can you share your .inc file with me? I want to compare it against mine and the one that comes with 029v. Mine is extremely close to 029v (within about .5%), which is set up for a (the?) GM sensor. So I'm wondering if I have something else going on, like incorrect bias resistors or something. I've got a few mods to do to my board (TPS, Boost Control, Fan Control) so I'm going to poke around with the multi-meter a bit before I do a reflash.
-Mike
-Mike
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