IAT Sensor Mod Experiment

[lca13]

I been thinking about doing this... pretty easy to try... I have a 5K pot to use and would just run it into the cab and using an ohmmeter, set it initally to what it should be based on air temp, and then adjust "small amounts" after that.

But the O2 sensor has the final verdict... all the inputs are for the ECU to guess correctly then verify after the fact, so I am under no impression that I can simply move the AF curve left or right much with this simple mod.

Another idea.... how about an oscillator that applies a voltage or ground to the o2 circuit peridically, thus overriding the actual output... the frequency could then be increased to send increasing "rich" signals to the ECU... has anyone tried this?

[parasonic]

There is no need for an oscillator. The value coming from an O2 sensor is DC.

[lca13]

>>There is no need for an oscillator.
>>The value coming from an O2 sensor is DC.

No,, not was I was thinking.... a motor or oscillator that could close a circuit with a certain adjustable frequency to ground the output of the o2 periodically... something that would allow an increase in the fequency of the "rich" reading feedback to the ecu... something you could adjust from no change to a little to more... etc.

Wonder if something like that would work... just thinking about it.

[Snax]

There are piggyback fuel computers that can do just that. I believe most of them offer rpm and pressure dependent compensations.

[88HF]

I think the potentiometer idea has merit. If you had a pot that only controlled the range of acceptable values the IAT would send.

[kitcar]

Originally Posted by 88HF

I think the potentiometer idea has merit. If you had a pot that only controlled the range of acceptable values the IAT would send.

Taking the IAT out of the circuit completely and replacing it with a POT would work great! Even if the O2 sensors sneak the mixture back up, you'll still have an ignition timing advantage over the stock sensor.

I've been reading this tread with a lot of interest. I did the IAT deal on my '99 Dakota; it's an old trick for Dodge trucks and Jeeps for a few free horsepower and torque. The problem with most of these things is that the colder the air, the higher the resistance so when you add a POT or resistor to them they think it's colder, so they advance the ignition timing, thus you need to clip the wires and make a manual IAT or even just have a series of switches with different values. Turn them all off and you're at 0k and the vehicle thinks it's a million degrees.

I had a couple of scares when I had mine hooked up. In cold weather with the adjuster turned all the way down to 4k or so, the thing would stall from lack of timing and fuel - so care has to be taken when using them. First time it happened I thought I threw a rod.

This is the Dodge/Jeep/Chrysler baseline for the IAT; most should be similar.
Air temp........resistance
32 deg. 29,000 to 35,000 K
50 deg. 17,990 to 21,810 K
68 deg. 11,370 to 13,610 K
77 deg. 9,120 to 10,880 K
86 deg. 7,370 to 8,750 K
104deg. 4,900 to 5,750 K

[dieselbenz]

I'm reviving this old discussion after I put together my own IAT sensor pot and wiring harness.

I haven't installed it yet but I'll update here as it progresses.
According to my BMW repair manual, the AIT sensor in this car outputs 2.5k ohm at 68f and 830 ohm at 122f. I'm using a 5k ohm pot.
http://farm4.static.flickr.com/3104/...8bf16fe5_o.jpg
The repair manual goes on to say that the ECU uses input from the IAT sensor to retard spark timing as air temperature increases. So in theory at least, colder IAT signal should increase both power and fuel economy... slightly. The beauty of using a pot instead of resistor is that I can check my instant fuel consumption at both extremes of the temperature range and everywhere in between simply by turning a knob.
I mapped out the pot for the 2 known data points. BMW claims that at operating temperature, the intake air temperature should be between 122-158f. Because of the high intake temperature, high compression ratio and lack of knock sensor, BMW requires minimum of 91 octane at all times. My goal of this project is to be able to run the car on 87 octane without compromising fuel economy or performance. The first step was to bodge together my own cold air intake through the inner high beam headlight. Its a sealed forward facing intake that takes advantage of the oncoming air for better throttle response and bit more power. According to some, this kind of intake can also improve fuel economy but I'm not quite sold on that front.

With just the intake, I already have it running on 87 octane without a hitch. Now we'll what happens when I take manual control of the AIT signal.

To be continued.
Justin

[happybobcat]

Originally Posted by Jim Dunlop

Why not just remove the IAT from the airbox/intake and move it closer to the engine?

because you a MIL and it reads -40F if you do.

[Jay2TheRescue]

Originally Posted by happybobcat

because you a MIL and it reads -40F if you do.

Huh?

[GasSavers_Erik]

Given the meaning of MIL, the topic (IAT sensors) and -40 degrees, here's the way I understand it:

"If you mess with the IAT sensor on your mother-in-law's car and it runs poorly afterward, she will likely give you the -40 degree treatment".