Your A/F ratio should actually go the other direction if you are trying to link IAT to air density.

60 deg F air has a density of 1.22 kg/m3.
90 deg F air has a density of 1.16 kg/m3

The higher the density the leaner the charge if fueling stays the same. With that said, your car should be richer when it is 90 deg F out than when it is 60 deg F out.

If your A/F is going the other direction I would chalk it up to MAF error, O2 error, or ECT skewing.

 

Heatsoak...


That's still my theory at least. I've relocated the IAT to get rid of that and get a true IAT reading. Now, the trick is setting the Charge Temp Blending table correctly. That's what Marcin's working on. Hopefully, his math skills will have us an answer (procedure) to do this properly.

 

I'm subscribing to this one.I too have relocated my IAT sensor to the airlid in my F-Body.I have a Z06 maf that has it built in but instead of using it I decided to use the one in the stock location instead.I've gone back and forth between the one in the maf and the stock location and see an upwards of 10 degrees hotter through the maf.I'm waundering how much this helps me out if any?Traver

 

I get faster, lower temp readings after relocating the IAT sensor to just in front of the air lid. This captures the temp of the air entering the base of the lid/filter. Any increases in temp should be taken care of with the Charge Temp Blending tables.

 

Thats also what i've seen. Normal running temps from 80-110 degrees the car pulls timing and im slower. When I put the resistor in it says its 57 degrees and no timing is pulled and I can keep up better with my buddy.

 

Fact. Moreso in Mafless tunes that rely on the VE table (and/or backup VE table) exclusively.
VE table values in GM units are specified as: g*K/kPa.

Where g = grams of air
K = temperature of air charge in degrees Kelvin
kPa = Manifold pressure

g is calculated based on the stored VE table value, K, kPa and RPM. With incorrect IAT values, K will be inaccurate, and subsequently fueling will be incorrect.

 

who cares what the air temp is at the front of the air lid there is alot of heat soak there suprised that mine is better next to the throttle body,also changed my bias numbers so the pcm doesnt respond as fast to temp change.

 

Well...I guess it depends on where you put the IAT. The natural flow of air through the front bumper is rather decent. You don't have to have a ram air hood to get decent IAT temps. A simple test....after a drive, pop the hood and feel around just behind the washer fluid reservior. It stays nice and cool becase of the airflow.

 

why not adjust bias accordingly instead of setting it to some arbitrary values?

 

i actually got the idea of changing my bias from you and JIMMYBLUE i put thermo couples in a few spots in my intake tract before i moved my IAT everywhere gets heat soak some faster some slower i just wanted to know the exact IAT of the air entering just before the engine thats all.

 

Yes the PCM uses the IAT to adjust fueling, but it is not a significant difference for most driving conditions.

Theoretically the IAT should skew fueling +/- 6.2% (0 to 40 deg C)

With charge bias this value drops below 5% for nearly all driving conditions.

This is a drop in the bucket considering a 5 kPa change in MAP is a 7% shift in density/fueling alone.


Yes it affects it, but it isn't going drive your tune far off if your IAT isn't exactly on. Like I said, my IAT isn't even connected and I'm 3bar SD.

 

i'm not seeing how you arrive at these numbers, care to elaborate?

 

Air Temperature Effects on Air Density (Ideal Gas):

Air Density = (Pressure * Molar Mass) / (R * Temperature)

65 kPa @ 0 deg C

Air Density = 0.65 * 28.966 / 0.083144 * 273.15
Air Density = 0.829 kg/m3

65 kPa @ 40 deg C

Air Density = 0.65 * 28.966 / 0.083144 * 313.15
Air Density = 0.723 kg/m3

Deviation +/- = (1 -(Low / High)) / 2
Deviation +/- = 1 -(0.723 / 0.829) / 2
Deviation +/- = +/- 0.0638 --> 6.38%


Air Pressure Effects on Air Density (Ideal Gas):

Air Density = (Pressure * Molar Mass) / (R * Temperature)

60 kPa @ 15 deg C

Air Density = (0.60 * 28.966) / ( 0.083144 * 288.15)
Air Density = 0.725 kg/m3

65 kPa @ 15 deg C

Air Density = (0.65 * 28.966) / (0.083144 * 288.15)
Air Density = 0.7858 kg/m3

Deviation = 1 - (Low/High)
Deviation = 0.07692 --> 7.69 %

 

Because I'm bored I made a chart that shows the change in air density for MAP and IAT.

I tried posting a picture of a log which shows how my the a/f of the car hovers around the the target a/f of 14.2 even though the IAT is flatlined at 14 deg C. The day was an 80-90 deg F day even though the car was tuned in a 60-70 deg day.

 

Here is my target a/f. Note the flatlined IAT. The spikes are me shifting.

I always connect the IAT for all of the other SD tunes that I do.

I left mine out temporarily when I first did the tune and then just left it out because oddly enough the a/f hardly even notices it being jumpered.