Using a potentiometer instead of IAT

Synned · Aug 9, 2006

Well since I have replaced my temp sensor with a resistor, by car is fixed. It used to hesistate and be really sluggish when it was hot out. That is all fixed due to 43k ohms of resistance instead of the IAT.
I was wondering if you guys think it was a good idea to replace the resistors with a potentiometer, so that I can adjust the ohms according to how hot it really is outside.
Would that work for an application like this?
Why does a potentiometer have three connectors? Input output and ground?

reddy351 · Aug 9, 2006

"Why does a potentiometer have three connectors? Input output and ground?"

Not technically "input, output and ground" There is a "tap" that is the third (usually the center) lead. It is the one that wipes across the resistor to vary the resistance. The other two leads are going to always be the same, as these are across the whole resistor.

tjh566 · Aug 9, 2006

somebody did their homework... I dont see why it wouldnt work, you just need to figure out what resistances you need.

OrangeMustangGt · Aug 9, 2006

I'm also interested....anyone know the ideal resistance?

what are the negatives of using a fixed resistance?

urban96 · Aug 9, 2006

im pretty sure those $20 performance chips people try to sell on ebay do the same thing

Synned · Aug 9, 2006

urban96 said:
im pretty sure those $20 performance chips people try to sell on ebay do the same thing

Yeah, they do, but they aren't variable. I think those are one temperature resistors.

I will make markings on the knob, showing the temperature at that resistance.

I'm going to pick one up from radioshack tomorrow. I'm goign to get the 100k ohm, or the 50kohm if radioshack has it. 100k is overkill...

I'll let you guys know how it goes!
BTW I think after changing the IAT to a resistor my mileage increased a ****load as well. But I was having problems.

Synned · Aug 9, 2006

GreenMustangGt said:
I'm also interested....anyone know the ideal resistance?

what are the negatives of using a fixed resistance?

50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms

^^^^Thanks to jrichker.

I think a 50k ohm potentiometer would work great, and i would mark the temperature around the knob. Right now im using 43k ohm and the car is running strong in the heat, no pinging either.

donjohn · Aug 10, 2006

Do you actually need the three terminals? A "rheostat" only has 2 terminals and varies the resistance. A "Multiturn Preset" is like a pot but way more precise.

with the presets and the potentiometers, if you only need a variable resistance, you're only going to use 2 of the 3 prongs

tmoss · Aug 10, 2006

I don't want to dampen your enthusiasm guys, but take a look at how much timing we're talking about due to ACT input..........

Synned · Aug 10, 2006

I am positive that the only thing the act was doing was pulling timing. I fully beleive that for some reason it was also changing the a/f ratio. this did not just feel like a few degrees of timing . . . i know what that feels like . . my car felt like i lost two cylinders . . by the way i am posting from my cell phone coming home from six flags in new jersey . . what a great time .

tmoss · Aug 10, 2006

If the ACT was bad and you went to a resistor, you might feel that big a difference. If you took a good ACT out and put in a rheostat, I don't think the difference would be as great.

You're really wired man.........

Synned · Aug 10, 2006

tmoss said:
If the ACT was bad and you went to a resistor, you might feel that big a difference. If you took a good ACT out and put in a rheostat, I don't think the difference would be as great.

You're really wired man.........

Well see, thats what i would think, but I tried changing the ACT wayyy back and it made no difference to my problem.

But true, if your act is working properly there would be no point to this, but for my application for some reason switching to a resistor made all the difference in the world, even when a new act didn't do anything. Maybe I'll pick up a new new act and try that one.

badstang123 · Aug 11, 2006

I've been extremely happy since I switched to a resistor as well. It has been a noticable difference. All the theories in the world are great but here's a link to someone who has actually dyno tested this and gained 7rwhp on a 4.6.

http://www.dfwstangs.net/tech/cppp/CPPP.htm

tmoss · Aug 11, 2006

badstang123 said:
I've been extremely happy since I switched to a resistor as well. It has been a noticable difference. All the theories in the world are great but here's a link to someone who has actually dyno tested this and gained 7rwhp on a 4.6.

http://www.dfwstangs.net/tech/cppp/CPPP.htm

Did you read the bottom paragraph of the that dyno test?

"I don’t see any need for it on the street, as the computer "learns" your trick in a very short time, and adjusts accordingly, often hurting performance until the next battery reset."

If you erase KAM with a battery disconnect your going to notice more power also.

Synned · Aug 11, 2006

tmoss said:
Did you read the bottom paragraph of the that dyno test?

"I don’t see any need for it on the street, as the computer "learns" your trick in a very short time, and adjusts accordingly, often hurting performance until the next battery reset."

If you erase KAM with a battery disconnect your going to notice more power also.

This wasn't even close to 7rwhp...it was more like 50... and I'm not exaggerating.
I don't know why it was like this, but something when it was hot out triggered my car to get killlllled. No throttle response whatsoever, and then huge missing power throughout the rpm range.

Using a resistor fixed this, I don't know exactly why though. I'm going to get another act as I said and see if it clears up, but I doubt it I have the EXACT same problem with this new one. And it can't be the wiring, cause the resistor works great.

MLC Stang · Aug 11, 2006

Guys,

The ACT and ECT sensors have a much, much greater effect on A/F ratios than on spark. In fact, the two sensors combined perform the job that used to be done by the choke on a carburetor.

Here’s ten pages out of the Charles Probst book with complete info on the ACT and ECT sensors. (I posted this information some time ago, and it’s still out there.)

http://www.usnaaaa.com/pingisgone.pdf

At any rate, be careful what you calculate. The ACT and ECT are both thermistors, which have a negative temperature coefficient, i.e. their resistance DROPS as the temperature increases. That’s the opposite of a standard resistor. (This is due to an internal fixed-value resistor wired in series with it.)

You can see by the chart on page 275 that if you put a 50 K-Ohm resistor in place of the ACT, the computer will think that the incoming air temperature is always about 58 or 59 degrees F. So, when it’s really hot outside, your engine will be running pig rich.

You could do a much better job of this (controlling A/F ratios) with something like a Pro-Flow Remote Optimizer.

Just some thoughts. But, hey, if the resistor is doing the job for you… great!

Synned · Aug 11, 2006

MLC Stang said:
Guys,

The ACT and ECT sensors have a much, much greater effect on A/F ratios than on spark. In fact, the two sensors combined perform the job that used to be done by the choke on a carburetor.

Here’s ten pages out of the Charles Probst book with complete info on the ACT and ECT sensors. (I posted this information some time ago, and it’s still out there.)

http://www.usnaaaa.com/pingisgone.pdf

At any rate, be careful what you calculate. The ACT and ECT are both thermistors, which have a negative temperature coefficient, i.e. their resistance DROPS as the temperature increases. That’s the opposite of a standard resistor. (This is due to an internal fixed-value resistor wired in series with it.)

You can see by the chart on page 275 that if you put a 50 K-Ohm resistor in place of the ACT, the computer will think that the incoming air temperature is always about 58 or 59 degrees F. So, when it’s really hot outside, your engine will be running pig rich.

You could do a much better job of this (controlling A/F ratios) with something like a Pro-Flow Remote Optimizer.

Just some thoughts. But, hey, if the resistor is doing the job for you… great!

'
You know, after reading that a lot of things make sense.
I think I might have extra resistance somewhere in the act circuit. That would make sense, because I also have horrible cold starts. Does anyone know the pin locations on the ecu so I can check the resistance of the resistor there and see if it is still around 43k ohms?

I'd love to figure out this problem, I'm glad I just figured out these hard cold starts are probably directly related to my weird act problem. I want to figure out the resistance of the act at the ecu.

BlackVert · Aug 11, 2006

Synned said:
Does anyone know the pin locations on the ecu so I can check the resistance of the resistor there and see if it is still around 43k ohms?

http://www.innovatemotorsports.com/resources/1994_1995_Ford_Mustang.php

badstang123 · Aug 11, 2006

tmoss said:
Did you read the bottom paragraph of the that dyno test?

"I don’t see any need for it on the street, as the computer "learns" your trick in a very short time, and adjusts accordingly, often hurting performance until the next battery reset."

If you erase KAM with a battery disconnect your going to notice more power also.

I did read the whole thing. And that is part of the reason I thought it was a good write-up. It showed both the up and downside. It's much better than a one sided view. It's working well for me...so I'm leaving it for now. Plus things could react differently on the 5.0 computer as opposed to the 4.6's.

Synned · Aug 11, 2006

BlackVert said:
http://www.innovatemotorsports.com/resources/1994_1995_Ford_Mustang.php

I would just check voltage there, right, since I can't check resistance?

Thanks
Joe

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