So, as the title requests, what is it all about?

Obviously, it is an air intake temperature sensor.. most of 'yall have one that lives in a tap in the keg- some have one that lives in the hat of your CAI or 14x3.. Mine lives in the duct halfway between my CAI filter box and TB hat..

I found an article on this thing some time back, but didn't take heed.. it's got my full attention right now.. I'll get to that later.. My present questions are:

1- when does this thing matter? open loop? closed loop? always?
2- how much influence does it have on things such as a/f ratio. timing advance/retard?
3- does it make adjustments in minute increments, or in stages?
4- does it measure air volume passing by it in any manner?

thanks, as always!

 

I don't know how it's used in the engine performance management. I'm presuming it's some form of feedback to alter air fuel/ratio since air density is related temp, see universal gas law.

Our air temperature sensors are transducers which put out an analog voltage that's proportional to temperature. The computer uses it to represent temperature in making it's calculations to determine settings for the various engine performance parameters. Ours are analog as opposed to the digital type which send out digital pulse trains representing temp.

If your asking what the computer does with this info....well I'm listening too. Seems like this info is more closely guarded than fort knox but clearly there are some who figured it out, aka hemifever, B&G chrysler, etc...As the Chinese all say when my company visits and does an install....Can we have the source code? We promise not to reverse engineer your system.

 

Yep. It clues the PCM in as to what the intake air temp is.... The PCM then uses this info to minutely adjust injector pulse-width (and thereby, fuel mixture ratio) mostly in open loop, when it doesn't have the O2 sensor to tell it what is REALLY going on. Once in closed loop, it does have some small bearing on timing on our engines...... but, that's about it. (and it may not even do that....)

Is this some magic bullet that you can modify the signal and eek more power out of your engine? Well, for the few short minutes it is in open loop, sure. But, once the engine hits closed loop.... so much for that.

Will it give up "up to 60 horsepower, and 5 miles per gallon"?? Hell no. If it had the much effect, do you think our trucks would be getting single digit fuel economy from the factory? Wouldn't something like that have shown up on our trucks right from the showroom floor?

The IAT sensor is a very minor player in how your engine runs. It would run just fine WITHOUT it, but, would set a code, and that damn CEL can be annoying. Computers can be real picky about those things. It knows it should have that sensor, so, by god, it WANTS it. A lot like Number 5..... Give me INPUT!!!

 

It is one of the sensors involved in how the PCM controls the air/fuel ratio.
http://www.aa1car.com/library/air_temp_sensors.htm

 

fwiw- here is where I'm at, and why I'm asking:

Since the FI, I've ran cooler.. since I burped it really well, I don't run as cool as I did w/ air in the system.. I adjusted my efan controller higher, and I strongly considered a 195* stat.. then realized- the temperature of the truck isn't that cool, a matter of fact- it's likely no cooler than it was before I pulled the keg.. but I still get a periodic p1281..

I've determined it's my AIT causing the fault.. with the ram air hood and the move from the keg to the CAI duct, that AIT is cooler than it has ever been when the truck is operational..

So- the AIT plays a role in a/f before loop closes, and pretty much timing alone after loop closes.. the o2's pick up the primary role of a/f after loop closes.. but the only place the engine can determine where the spark can be best applied (o2 laden cool air, or o2 deprived HOT air) and advance or retard spark, is the AIT.. I'm thinking the coolant temperature plays a role too, but not as much as the AIT in this regard..

I'm running rich- not terribly rich, but rich.. at WOT, and the engine running Open Loop/lookup tables, it's not rich.. once loop closes and the sensors take over completely, it starts rich'n up..

Given, that air coming into the hat is much colder than most folks have due to the ram air, still- I don't want that kind of gas being thrown at it.. it's counter productive for providing power- what I want is a good ambient temperature reading so that the spark is adjusted correctly.. and less gas tossed at it.. which should improve mileage while improving power (short of WOT, if you can follow that).. I have no use for WOT- I can count the times on one hand I go that deep in the throttle..

you hit close HeyYouNinja- this is the area all those eBay chips attack w/ huge promises.. I don't believe them and won't touch it- especially with a non variable resistance device.. what I'm addressing and asking about is the same principle, but without the BS.. that is where I'm at with this... here is the next series of questions:


Does the AIT measure, through whatever scientific equation residing in the PCM, air VOLUME passing by it? This is a crucial question I'm researching to find out if I should pull the AIT out of the duct and put it somewhere else that won't allow it to be so cool.. If it DOES NOT, I could potentially expect the PCM to adjust by pulling fuel (run leaner) and retard timing.. The retard timing I don't want, the pull fuel I do want..

Like I said, if it pulls fuel- my power should increase a small degree, which is good, but the fuel usage should also curb a touch..

bottom line: the eBay gadgets are BS.. but not pure BS.. there is a sliver of truth to the principle, though they blast right pass that and focus on the BS.. I wanna address that sliver and see what happens.

sorry for the novel.. there is a lot to address with this thing as it turns out.

 

I dont really see a reason that it would need to measure air volume. Due to the earths atmosphere being largely the same pressure; a given volume of air's only density variable is temperature, which is where the AIT steps in.....If that makes any sense at all...... I know what I mean, explaining it is the hard part


EDIT: to put this better: a cubic centimeter of air is always going to be the same volume (1cm^3), but how many molecules of air are in it (density) is determined by the ambient temp (and altitude). Same goes for a cubic yard, etc., etc. In the case of the engine, knowing the VOLUME is not very important (the needed volume constantly changes depending on throttle location), but knowing the DENSITY is. The MAP measures needed volume, and adjusts a/f accordingly.

 

yeah, I'm thinking the MAP handles all those concerns, and not the AIC.. it would be a difficult task for the PCM to crunch the info and adjust quickly enough to make the adjustment by using the AIC (by my reckoning).. but I thought I'd ask..

I'm going to move that rascal..

 

Mad nailed it. The IAT sensor plays a role, along with MAP (manifold absolute pressure) sensor to determine air flow. (or, the "mass" of the air.)

Pressure X Volume = Mass X a constant.... X temp. (PV=MrT)

Volume, temp, and the constant are known here, so, the PCM just shuffles the equation to determine mass, and adds gas accordingly. (granted, changing manifolds also changes volume, and that may skew the calculation.....) However, in closed loop, the O2 sensor should figger it out. If you are running rich under normal circumstances, I would take a long hard look at the O2 sensor first.... and if its questionable, replace it. (don't use bosch, they suck) NTK (NGK?), or OEM is the way to go here.

At better than somewhere between half, and three quarters throttle (not necessarily wide open throttle....) the PCM will drop into open loop in any event, and run off its tables. Being a little richer here after a manifold swap isn't really surprising. You would need to adjust whatever variable/table/value/whathaveyou to correct that situation. (I haven't dug that deep into custom tuning YET.... so, don't have hard data for that.)

 

man, if it were manifold alone I wouldn't worry about it at all- the 'puter would figure that out in short order.. My problems are bigger than that.. but even said, the issues aren't hurting my feelings.. explanation:

in addition to the FI, and the ram air, I also upgraded injectors.. I run the genIII 4 hole furd racing 21#r's.. which according to fiveO were direct replacements, but it turns out it was NOT.. those injectors aren't rated at industry standard 43.5psi, they are rated at 39psi.. we know our trucks run 49psi.. the math isn't constant I've learned.. in short: if you had two injectors rated at 21# at 43.5psi, and jumped the pressure to 49psi, you may have one now producing 26#, and the other 23#.. the increase/decrease isn't constant between differing injectors..

So, Sean- aka HemiFever, did the math on my injectors and determined I'm pumping 11% more juice to the cylinder.. he curbed it 5% and got me close.. I've yet to install the WB A/F that's sitting in my tool box, but the USB/OBDII tells me I'm pretty close to 12.3:1- which is rich, but not terribly rich..

My thoughts are centric to basically moving the AIT to better serve me in closing the duty cycle some on those injectors- if I can..

don't get me wrong now.. I'm getting 13.5mpg overall mileage.. that is with 35"x12.5" tires, and 4.56:1 gears.. But- the science of the matter tells me I can get better yet by leaning down the a/f, and getting an accurately adjusted timing on the thing.. if that is as simple as moving the AIT to a place where it will get a hotter read than what is actually happening, I'm all about it.

see where I'm coming from now?

edited to add: I'm running cool too.. that may simply be a matter of the AIT, or the coolant sensor.. BUT- it may also be a result of running rich.. running rich means running cooler as opposed to running lean- hotter/more powerful explosion..

 

I think you want WOT ratios around 12.7 or so in any event, so, you are damn close.

Isn't there an adapter between the intake, and the TB? Removing that, and drilling it for the sensor might get you closer.... putting the sensor into the plenum (what little there is of it on that manifold...) would be closer to the 'ideal'... but, can you do that without removing the intake?