IAT Resistor/Modules Vs. Performance Chips
What are those infamous IAT resistor mods and performance modules and how do they compare with real EPROM racing or performance chips? Need a guide to try it out by your self? Find out here…
What are performance chips (Real EPROM or ROM Chips)?
Chips = Memory Chips = EPROM or ROM (Erasable/Programmable Read-Only Memory)
ECU = Car Computer (Engine Control Unit)
Just like your PC, car computers or ECUs have a CPU (Microprocessor or Microcontroller), RAM memory and a boot device. In their case, EPROM chips serves as the boot device, instead of a hard disk. These EPROM chips contain the ecu’s operating system and operating parameters data, and hold it even if the power is removed from the ecu for any amount of time, even years, due its internal architecture.
<– Real EPROM Chip
These EPROM chips were used on Non-OBD (1988-1991) and OBD-I (1992-1995) cars. In the case of the newer OBD-II cars (1996 and later), manufacturers use a different approach, being either an EEPROM (also called E2PROM) or (more commonly) FLASH ROMs. Both methods are very similar to an EPROM device type, but with newer features, like on board re-programming for example. All types of these ROM, EPROM, EEPROM and Flash memory chips, or simply “chips”, are called memory chips and so we will call them in the rest of this article.
Once you put your car key to “ignition” or “on” position, it powers up the ECU, among some other circuits, and right after it is powered up, it immediately boots from the memory chip and reads the operating system from it, which is the program that will run and control the ecu itself and the engine. It does things like reacting or responding to the various sensor readings. The ECU will also read from the same memory chip, the parameters data, which is the data that will tell the ecu how much fuel to inject, how much ignition timing to apply, what to do if the engine is hot or cold, etc.
What changes these real chips do:
When an aftermarket memory chip is installed in your car’s ECU, you are changing the program or operating system running it. It could be either slight changes or a major reprogramming, depending on the intended purpose and the chiptuning Company. The new parameters programmed on that new memory chip will hopefully affect the behavior of the ecu and its response to the different signals received from the various engine sensors in a positive way, aimed in the direction of more power, or to accommodate new engine hardware like a Turbo system, aftermarket camshaft, or any other modification that require an ECU reprogramming. The result will be a change in performance that will depend on the program written in the chip.
Some of the changes done to these aftermarket memory chips are (1) disabling the vehicle speed limiter or governor, allowing the vehicle to reach its maximum natural speed, (2) the RPM limiter or revlimiter is slightly raised, allowing higher engine speeds for an extra punch when shifting and (3) the fuel and ignition tables (maps) are are changed or “remapped” for optimum fuel delivery and ignition firing.
What about the IAT resistor kit, IAT mod, etc?
IAT Sensor = “Intake Air Temperature” sensor
AFR = Air/Fuel ratio, ideally it would be 14.7 units of air to 1 unit of fuel or 14.7:1 (lambda 1)
The IAT sensor is a passive or discrete electronic component that will simply vary its resistance depending on changes in temperature (also called a thermistor). It has a negative coefficient, meaning that the higher the temperature is, the lower the resistance it will offer to the current flow and vice versa.
Different IAT sensors (external to the MAF):
When a voltage is applied through a resistive network (shown below) of which the IAT sensor is part of, the output voltage from that network (“To ECU” in the drawing) will vary or “swing” according to the temperature of the air passing through the IAT sensor. This swing is caused by the mentioned variation of resistance of the IAT sensor, that at the same time causes variation in voltage drop. The voltage fluctuation at the output of the resistive network will be interpreted by the ECU as a direct reading of incoming air temperature variation.
So why the ecu needs to know the incoming air temperature?
The answer is a simple fact of physics. Cold air is denser than hot air, having higher mass by volume, meaning more oxygen content. The importance of this, is to allow the ecu to modify the Air/Fuel Ratio (AFR) to acceptable levels, so combustion inside the engine can be kept at optimum levels, allowing optimum engine power, preventing engine from knocking and having lower nitrous oxides (NOx) emissions. It helps to the understanding of this, knowing that a mixture of air and fuel (gasoline in this case) will only be highly flammable at certain proportions. Too much air, too explosive. Too much fuel, will burn too slow or won’t ignite at all. The engine will theoretically need around 14.7 grams of air to every gram of gasoline.
Few ECUs will use the signal from the IAT sensor alone, to modify the ignition and / or injection to slightly compensate for the incoming air temperature variations. So making the computer “think” the incoming air is cold will make it do small adjustments to ignition timing and / or fuel injection and there is where the IAT Mod ideal originally came from.
It is accomplished by putting a fixed resistive value (fixed resistor) instead of the regular IAT sensor, simulating a cold intake air situation. Going back to the facts above, “the higher the temperature, the lower the resistance”, to benefit form this modification, we would need to make the resistor value high enough to make the computer “think” that the temperature is low enough. That would hopefully induce the ecu to inject more fuel and advance ignition timing accordingly, in an attempt to compensate the supposed incoming cold air.
The problem with the IAT modification:
Even more and more people that have bought those IAT mods are claiming that it does nothing. It is probably attributed to the fact that not all cars depend only on the IAT sensors alone to make the necessary changes. So, it is very probable that modifying the IAT sensor of your car will do nothing, or at least nothing noticeable.
If you successfully modify the IAT sensor and the engine makes some noticeable changes, remember that the air will not be truly colder or denser, so no extra oxygen will really be present, ending up in a richer mixture, higher emissions and very probably lower performance, unless your car is already running way too lean because any previous modification or any existing engine problem and a richer mixture will benefit its performance.
If you live in a cold area, you will notice no difference as the original IAT sensor installed in your car will already be in a better resistance value than the one you would insert. If you live in a hot area (tropic, desert), it will be worse than the ones in a cold area, as even less oxygen will be available for the combustion. If you live in a high altitude area, you will have similar or worse luck that the ones in the hot areas as oxygen and pressure progressively decrease with altitude, even if it’s cold.
Regardless of the all mentioned above, if you finally make the car computer do a positive modification by installing that 10 cents resistor, remember that changes will be on the factory program range limits or specifications anyway, as the chip or computer program is still the factory installed one. All changes made by sensor modifying (any sensor), will stay in the factory specs since sensors can be read but can not bypass or override functions in the ECU, unless a memory chip with a modified program (performance chip) is installed.
Don’t take my word!!!
Please, don’t just take my word about this. You can experiment it yourself if you are a little skeptic about this or just want to try it (I would do).
Do it your self:
All IAT sensors resistance, average from about 4700 to 5000 ohms (4.7K-5K) when the air temperature is cold enough to make an adjustment on ignition timing and / or fuel injection. The trick is to replace the IAT sensor by a resistor with a “cold temperature” equivalent resistance value, similar to those mentioned above.
NOTE: For easy calculating the resistor you need, just use the online resistor color code calculator: Resistor Color Code Calculator
All IAT sensors have two wires, but though many of them are installed alone in the incoming air path elsewhere after the air filter, some of them are incorporated inside the MAF (Mass Air Flow) sensor assembly. In that case, the MAF sensor connector will have 4 or 5 wires, where 2 of them will be connected to an internal IAT sensor. You will either need to find the stand alone IAT sensor in the incoming air path or identify the wires connecting to it on the MAF sensor connector if it is internal.
In the first case, the installation is done by disconnecting the plug to the IAT sensor and inserting the resistor leads, making contact with the IAT sensor plug connections (the part that goes to the ECU and NOT the part that goes to the sensor).
In the internal IAT sensor case, you will need to cut the two wires that connects to the internal IAT sensor to some length, to attach the resistor. Using the picture bellow as reference, if for example the IAT sensor is connected to wires 1 and 3, you should cut where the two green crosses (“X”s) are in the picture and attach, either by soldering or by using wire nuts, the fixed value resistor you chose for your car at the pair of wires that go to the “ECU” direction. You must cover the other remaining two cut wires with electrical tape or better, with a terminator connection for protection. Please note that the below example is just that, an example. Wires connecting to the internal IAT sensor can be any on every different MAF type.
You will be able to easily locate the internal IAT sensor by looking at the picture below. This will help in (1) knowing where to spray with the component cooler can when measuring for best value and (2) you can determine what wires are connected to it by using an ohmmeter, measuring between the IAT sensor leads and the connector wires.
Remember, you will electrically replace, but not physically replace the IAT sensor. That is, you will connect the resistor to the cables going to the ecu, but will leave the sensor in its place. The resistor, the same as the IAT sensor, has no polarity. That means that you can connect either wire with either resistor lead.
Now, since the resistor has a fixed value and the IAT sensor is out of the circuit, resistance will no longer vary with temperature. The car computer will permanently think that incoming air is very cold as long as the modification is in place.
After connecting the resistor, just make sure it is covered with tape or any other insulator and you can leave it hanging in a safe area on the engine bay as long as it doesn’t receive too much heat.
Now just do a test drive. How was it? Anything? No? No problem, you are not the only one.
As mentioned before, the resistance values of the IAT sensor averages between 4.7k – 5k, but if you want to try the exact optimum value for your car, just take out the IAT sensor, if it is the stand alone version of course, and put it in an ice bath prepared in glass or cup. Leave it submerged for 1 or 2 minutes and measure the resistance across the two connecting wires or terminal with an ohmmeter, preferable a digital one, in the 20K or equivalent range.
The measured resistance will be the optimal for your car. Probably you won’t find an exact commercial value that matches the measurement, but you can get the closest one. For example, if it measures 4633 ohms, then a 4700 ohm (4.7k) is a very common commercial value and will do the job just fine. Color rings for a 4.7K resistor will be Yellow – Purple – Red with either a Gold or Silver fourth ring. Check on Google for other resistor values color code if need any other value; Key word = “Resistor Color Code”.
If your IAT sensor is the MAF type (5 wires) you can not submerge it as it will be damaged, but you may find a component cooler spray sold for electronic circuits thermal troubleshooting and spray it directly over the IAT sensor inside the MAF assembly and then measuring it with the ohmmeter before it warms back up. The only thing is that such spray will go lower in temperature than a simple ice bath.
Make sure that the MAF sensor is completely dry before installing it back, since cold spraying it will make some condensation moisture.
Now do the test drive.
I know, probably it was the same or worse. That is the result of 90% of the cases. The remaining percentage? Well, an 8% is placebo effect and the other 2% maybe people that succeed in putting fourth of an extra horsepower (1/4 hp) and are content with that.
What about those mysterious boxes called performance modules?
Those shiny small boxes called “performance modules” that comes for a variety of models and model years, mostly with 4 wires coming out of it or even with a power select switch or rotary power control are the same cheap resistor, boxed, given fake attributes and some of them added a fancy control (variable resistor or potentiometer) along with the fixed resistor or a switch to select from different resistor values or “power ranges”.
People no longer wanted to buy a 10 cents resistor for $15-$70, so they boxed it to make it look cool and hide it at the same time to avoid recognition, making people think that it is something way much more sophisticated than a simple, cheap and most of the times, non working resistor. Some sellers went farther than that, making people believe that the resistor was “tuned” specifically for your car model. There is no way of tuning a fixed part! Others use a resistor network chip and wire two of the leads to the outside of the box. Those chips are not semiconductors or anything alike. They just have several internal resistors in parallel of the same resistance value to save space in circuits. They just hook one of the internal resistors to the IAT.
The results, the same of the resistor alone… NOTHING!
Many people is asking me about what’s inside of the adjustable boxes. The truth is that it is all the same and results won’t change, but to satisfy everybody’s curiosity, they just add a variable resistor or “potentiometer”.
It is used to adjust the total resistance of the circuit. That is, instead of having a fixed 4.7K resistor as a total and absolute value, it is made adjustable by placing a potentiometer in series with the circuit.
Below is an example of this. In this picture, it is shown both pictorial and schematic versions for better understanding, along with direction of maximum and minimum resistance.
This time it is selected a resistor with lower value to be fixed as the minimum circuit value. That is, if the person doing the scam knows what he is doing.
In this case, minimum resistance will be the value of the fixed resistance, which is 220 ohms (equals to hot incoming air) and can be adjusted by turning the potentiometer all the way up to the sum of both resistors, which in this case will be 220+10,000 ohms = 10220 ohms, making it equivalent to very low temperatures.
Well, I don’t know about you, but I think this can called “IAT Module Demystified”…
You are welcome to leave comments.
Thanks for reading,
For real performance chips (not resistors) that will make your car pull real hard, visit the page below:
These are real and tested. Trust us when we are saying that you won’t find anything alike on internet. We will soon post about the truth about big chip companies. Keep “tuned”.
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