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Old 11-21-2007, 05:46 PM   #1
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Slightly different IAT mod

After my first post and thread, here's the idea I was discussing with cheapybob.

I see a lot of ideas about modding the IAT signal with resistors to obtain a certain reading equivalent to a desired temperature to get a leaner mixture. The problem with using a resistor in parallel is that it doesn't change its value and will affect the IAT negatively in some temperature ranges, like the cold temperatures.

I studied electrical engineering for a few years. Adding resistance to a circuit is easy, just putting resistors in series and they add up. Lowering resistance is a little trickier. I played around with the parallel resistance calculations and came up with this idea.

Why not use 2 IAT's in parallel? Yes that is what you are reading. 2 IAT's that are resistors that will both be changine values at the same time. Effectively, what happens when two resistors in parallel of the same resistance effectively total half of that value. I did some calculating and compared them with the corresponding temperatures for given resistance.

this is what I found out. At 0F, the mid range of the IAT is 24K ohms. two of them would divide that in half to around 12K. That falls in the range for +20F. Effectively you are bumping up your IAT reading by 20 degrees.

Now at the high end. At 140F temperatures, the IAT mid range is 690 ohms. Divide that in half and you have 345 ohms, which actually falls between 160 and 180F, call it 170 ish.

One thing cheapybob alluded to was cold start drivability issues when using a resistor in the IAT. I think this dual IAT mod will correct that and maybe even work better than a resistor.

I also did some tweaking of the idea by placing a resistor in series with one of the IAT's to do some further adjusting of the ending resistances at several different temperature ranges.

Anybody care to chime in and ask questions or share ideas, please do. Also, what I'm really looking for is what temperature reading you guys try to obtain in order to maximize your fuel economy. If I know that, I can further tweak these numbers and give you possibly a better way to do it.
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Old 11-21-2007, 08:31 PM   #2
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Sounds intresting but when you fool a fuel injected car into running leaner you run the risk of extremely high in cylinder temps. I'm not sure how much risk there is, but I'd hate to see some burned pistons when you could just raise the IAT through a HAI.
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Old 11-21-2007, 09:10 PM   #3
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I think this is an interesting and worthwhile idea for cars that accept it. I think the O2 sensor will overide the IAT with respect to mixture. For my Saturn I find it more useful not to trick the IAT sensor but just supply hot air to it.
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Old 11-22-2007, 02:09 AM   #4
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I know the electrical aspect behind this, not so much the functionality. I know a little bit about what cheapybob says he has rigged and I figured out that two IAT's paralleled would work much better than a resistor and IAT. I don't know what year his car is, if its OBD I or II, and that too might play a factor on whether fooling the IAT mod will actually work. I thought I'd bring this idea over here where you guys know more about the actual functionality of the IAT. I don't know if anyone has ever tried what I've outlined, and since I have a little bit of EET knowledge, I thought if an IAT mod is something worthwhile, I might have come up with a better way to go about it.
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Old 11-22-2007, 02:23 AM   #5
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Using 2 OEM sensors is a good idea....

With variable resistance (OEM) and static resistance in parallel or series the resistance curve would be different than using variable resistance (OEM) with variable resistance (OEM) in parallel or series.

Somebody should plot these out...maybe 4 different curves?

...

Haven't done it yet...but here are some other ideas

* mod whatever controls the open loop mixture...whether it is a coolant temp sensor or air intake temp sensor or ??? so that you lean things out some during open loop. Do need to be careful because this is also the state the engine will be in during WOT...which is when extra fuel is used to cool the engine. Might replace this cooling effect with water injection?

* also might need to have a cold start mode where the engine will run at OEM specs until warm enough to lean it out during later open loop (which probably occurs even when warm...transients?).

* then when the O2 starts to control the mix in closed loop...you'll need an EFIE for mpg gains.

Some engines go into O2 closed loop mode much sooner than others. I was using an EFIE on a 3 wire O2 and could only lean it out to a limited degree due to cold start issues...ran so lean it wouldn't go from the 1st few stop signs in cool weather.

quote:

"...start with high resistance (10k+ ohms) when putting them in parallel (leaner) and low resistance (100 ohms) when installing them in series (richer). Potentiometers can be used instead of fixed resistors for ease of adjustment."

I think you can lean things out during cold start to some extent...but you'd need two circuits...a leaner cold start and an even more leaner open loop mode for running out of closed loop...when warm and the O2 isn't controlling things. You need a way to switch between these circuits...either manually or a timer or better....a thermally activated switch as found on some parts car.

Instead of using resistors...you can buy a grab bag of pots at RS or online to allow adjusting things in the cabin as you drive. I have a few that have ~2 turns from 0 to 10K ohms.

note: this info is mostly from reading and not experience.
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Old 11-22-2007, 02:39 AM   #6
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Quote:
Originally Posted by ZugyNA View Post
quote:

"...start with high resistance (10k+ ohms) when putting them in parallel (leaner) and low resistance (100 ohms) when installing them in series (richer). Potentiometers can be used instead of fixed resistors for ease of adjustment."

I think you can lean things out during cold start to some extent...but you'd need two circuits...a leaner cold start and an even more leaner open loop mode for running out of closed loop...when warm and the O2 isn't controlling things. You need a way to switch between these circuits...either manually or a timer or better....a thermally activated switch as found on some parts car.

Instead of using resistors...you can buy a grab bag of pots at RS or online to allow adjusting things in the cabin as you drive. I have a few that have ~2 turns from 0 to 10K ohms.

note: this info is mostly from reading and not experience.
Those problems outlined in the quote with cold running are exactly the reason why I suggested using two IAT's because their values will always directly related to the actual temperature. On the low end, having two paralleled only sets it off higher by 20F. This might be manageable at cold running.

IAT's and CTS's are thermistors, resistors that vary with temperature variations. I've got the chart that outlines the resistance range for a specific temperature. Pairing two IAT's takes the guess work out of what value resistor to use because you will always know what the sensors' values should be at a given temperature. I've played around with the formula for awhile and the math behind this is sound. I welcome anyone currently using a resistor in parallel to their IAT to give me the specific parameters they are trying to get to, actual temperature and the desired readings, and I will figure out how to get to it with two IAT's, and if needed, a resistor in series with one of them to tweak it. BTW, pots are resistors, adjustable ones.
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Old 11-22-2007, 02:41 AM   #7
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Pardon my ignorance, but what is an EFIE? I know cars, but am not familiar with the acronym.
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Old 11-22-2007, 04:06 AM   #8
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Quote:
Originally Posted by froggy81500 View Post
Also, what I'm really looking for is what temperature reading you guys try to obtain in order to maximize your fuel economy. If I know that, I can further tweak these numbers and give you possibly a better way to do it.
http://www.gassavers.org/showthread.php?t=2160

"With the Scangage, if you watch IGN, you'll see it drop and feel the engine get real sluggish if actual air or water temps get above about 210. I think that's because it was retarding spark significantly when it detected preignition. It also seems to happen if I try to run it tricked to 242 degrees before the intake air is up to 80 or so, so I usually run it straight from the sensor a few miles to warm up before switching it to 242."

Depends on the car?????

EFIE:

http://www.eagle-research.com/products/pfuels.html

"Increasing the combustion efficiency of an engine increases the exhaust oxygen percentage. Most fuel injection engines use an oxygen sensor to infer the air/fuel ratio of the engine, the increased oxygen content in the exhaust is 'read' by the computer to be a lean mixture in the engine. The computer then adds extra fuel to bring the pollution back to 'normal'.Fuel Savers EFIE device

This problem led to the development of the Electronic Fuel Injection Enhancer (EFIE, pronounced Ee-Fy). The EFIE allows you to apply an offset to the voltage coming from the oxygen sensor, so your vehicle's computer is completely unaware that the oxygen content of the exhaust has increased."

http://www.brightgreen.us/feverbus.htm
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Old 11-23-2007, 05:00 AM   #9
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Well, my goal of looking at this mod from a different angle was to come up with something more automatic, something that wouldn't need any user input or adjustment. Some of the numbers I've seen for temperatures, both actual and modified, show me this needs some further thoughts and inputs.

I have some electrical knowledge to work a theory. What I lack is the equipment and time to try some of these ideas. I have the desk and the calculator, I just don't have the laboratory. This is why I've brought forth this here, to give a different perspective to those of you who have things like scangauges and the like to actually monitor these types of mods.

Some of the data I'm looking for are this. What is the typical normal operating temperature (engine warmed up) of both an unmodified air intake, and a warm/hot air intake? This is the baseline I need to know to work this from, the starting point. Also, what are the desired "modified" air temperature readings for optimal economy? I've seen 242f out there but issues over that I've also read about.
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Old 11-23-2007, 06:21 AM   #10
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I would first relocate the IAT sensor to different areas under the hood to see what gives you the best results...then I would leave well enuff alone...just my opinion.
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