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Old 11-28-2003, 04:09   #1 (permalink)
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Intake Air Temp Sensor - what are the resistances?? - i have an idea...

hey peoples, i need to know the resistances of the intake air temp sensor that ford uses on the I6, as i had an idea.

ok, so we know that most falcons run rich at WOT, even more so with cams and such.

the EECIV uses manifold pressure and air temp to figure out how much fuel to put in the cylinders, and i think if we can fool it (like you guys with autos fool the comp when you fit that shift kit) so it thinks the air is a lot hotter than it really is, by varying the resistance of the IAT sensor we can crudely adjust the air/fuel mix.

im hoping that the sensor has a low resistance for cold temps and a high resistance for high temps, that way with a but of mucking about we can figure out what resistor to use, and just solder it in series with the IAT sensor, which should lean the engine off a bit, by making the computer think the air is hotter than it really is (hotter air = less oxygen = less fuel)

this should give a couple of KW at the top and a bit better fuel consumption as well, and might even help the guys with cams get a better idle and power curve?

if it has a high resistance at low temps and a low resistance at high temps we will have to put a resistor in parralell with the IAT sensor, it would prolly have to be a pretty stout one, and might be a bit harder to figure out what resitance is needed.

any thoughts or comments or tech specs?
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Old 11-28-2003, 05:26   #2 (permalink)
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Re: Intake Air Temp Sensor - what are the resistances?? - i have an idea...

Resistance Ohms Temp degrees C

58750 10
37300 20
24270 30
16150 40
7599 60
3843 80
2069 100
Not a good idea to meddle with as you will move away from the optimal fuel air mix.
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Last edited by Aussiblue; 11-28-2003 at 05:34.
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Old 11-28-2003, 07:06   #3 (permalink)
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Re: Intake Air Temp Sensor - what are the resistances?? - i have an idea...

sure it will help at WOT, but what about closed loop lean burn cruising. It will run even leaner, i dont want to be the one with a burnt piston.
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Old 11-30-2003, 03:47   #4 (permalink)
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Re: Intake Air Temp Sensor - what are the resistances?? - i have an idea...

58750 ohms at 10 degrees??? shite....you sure its not 58.75 ohms?

Quote:
Not a good idea to meddle with as you will move away from the optimal fuel air mix.
that was my point - at the moment most of our (6 cyl) cars (mine especially) run too rich at WOT, if we can lean it a little we get more power as well as less fuel consumption - i think the guys at the SA dyno day all saw hp gains on a dyno with an adjustable fuel pressure reg on their cars, set to less pressure than stock = leaner mixtures.

Quote:
sure it will help at WOT, but what about closed loop lean burn cruising. It will run even leaner, i dont want to be the one with a burnt piston.
dont have to worry about that - at cruise the car is in closed loop mode - it pours in the fuel then checks the exhaust gasses to see if its too lean or too rich, then adjusts accordingly. the comp will learn fairly quickly to add a little more fuel than it thinks it should.

or you could put a switch on your throttle pedal that only adds the resistor to the circuit when the car is at WOT - easy.

i believe the optimum AF ratio for the I6 is about 12.7:1 or 13:1 of thereabouts, gotta figure out what amount of degrees temp above actual to send the computer to get it to go from 10:1 (which it is atm) to that figure...i suppose we would need to look at the fuel maps in the computer to get it right....or buy a few resistors and organise some dyno time, and just go trial and error.

is anyone keen to do this? i have a an aftermarket computer on order so its not a big deal for me, but if somone wants to save themselves the cost of a fuel pressure reg it might be the go.

what if we tell the comp that the air temp is 40 degrees instead of 30, we would need to get the resistance down from 24270 to 16150...anyone know how thats possible using a paralell circuit? i have totally forgotten how to work it out..
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Old 11-30-2003, 15:27   #5 (permalink)
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Re: Intake Air Temp Sensor - what are the resistances?? - i have an idea...

By putting a 48271 ohm resistor in parallel you would get 16150 ohms at 30 degrees. This is how the other temps would be effected:

Base temp : new resistance : new temp

10 : 26498 : 28
20 : 21041 : 34
30 : 16150 : 40
40 : 12101 : 50

While the 48271ohm resistor might be fine for the higher temps eg: 20-40, at lower temps the jump might be to high.

Keen to hear the results if anyone attempts this.
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Old 12-01-2003, 01:43   #6 (permalink)
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Re: Intake Air Temp Sensor - what are the resistances?? - i have an idea...

yeah...i thought as much - that it would affect the other temps too much.

48271 ohms eh...might try and pop in to jaycar tomorrow arvo and see what the prices are like - from memory resistors are pretty cheap?

weeman can you please post up the equation you used to arrive at that number?
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Old 12-01-2003, 01:51   #7 (permalink)
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Re: Intake Air Temp Sensor - what are the resistances?? - i have an idea...

Unless your buying a variable resistor the closest you will probably get is 47k. You should be able to pick one of these up for 5-10c.

Formula:

RT = (R1 x R2) / (R1 + R2)

or for more than two resistors:

1/RT = 1/R1 + 1/R2 + 1/R3 .....
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Old 12-01-2003, 04:17   #8 (permalink)
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Re: Intake Air Temp Sensor - what are the resistances?? - i have an idea...

Definately ohms. BTW there is also a voltage relationship:

3.9 V at 0 degrees, 3.1 volts at 20 degrees and 2.2 volts @ 40 degrees.

If you are close by I have a 4 litre bucket of variable resistors and could give you a few to play with.
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Old 12-02-2003, 01:36   #9 (permalink)
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Re: Intake Air Temp Sensor - what are the resistances?? - i have an idea...

Aussieblue: thats strange that the voltage goes down as resistance goes down - usually the way sensors work is they are fed a constant voltage (about 5V usually) and then earthed through the computer, which measures the voltage coming back to it, from whence it determines the temperature.

if it drops voltage at the same time then thats just stuffed us up big time.

and im in brisbane so im not exactly close by lol. thanks for the offer though!
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Old 12-09-2003, 17:00   #10 (permalink)
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Re: Intake Air Temp Sensor - what are the resistances?? - i have an idea...

hey daneil,

lets give this a go eh?

i'll get this clappa ea up and running, i've got a varible resister here, that has a knob on it that turns the level of resistance up and down,

we'll chuck it on a dyno, and have a bit of a play with it eh?

i'll sort the car our first then we'll give it a go,

here's hoping the engine will blow.lol

cheers.joe.
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