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The Free Mod Series - Part 3: Light Ecu Tuning

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So now we've done basic Intake and Exhaust upgrades, but are we taking advantage of it for it's fullest extent? No! Even if we've added next to nothing in power, we can still add a bit more power, and improve throttle response.

The stock ECU's are programmed to run as close to 14.7-1 Fuel Air ratio as possible. This is great for fuel economy and emissions. The drawback is that this ratio is not good for making power, or throttle response. It's too lean. For a N/A engine, we really want October to a 13.5-1 air-fuel ratio.


We need to add fuel to the mixture.

We've all seen the cheap-o Ebay "gain 22hp engine chips" that sell from between $5-$25.

They work by adding resistance to the I.A.T. Intake Air temperature sensor to make the ECU think the temperature is colder than it really is, in response it will richen the mixture.

The Problem

They don't work on Toyota's as discussed many times before. The ECU isn't fooled for any length of time before it reverts back to normal tuning.

The Solution

The intake air temperature sensor signal isn't the only one that can easily be modified so that the ECU changed the fuel mixture.

Enter the E.C.T. Engine Coolant temperature sensor. By placing a 500 ohm resistor on the ECT sensor wire going to the ECU, we can control what the ECU thinks the coolant temperature is.

By RAISING the resistance on the potentiometer, the ECU thinks the coolant temperature has dropped. In response it not only adds the corresponding amount of fuel, it advances the timing slightly as well!


After buying a 500 ohm potentiometer from an electronics store <cough> Radio Shack <cough> electronics store <cough>

Obviously this is a very simple mod, but many will shy away from it because you have to find the wire going from the sensor to the ECU.

Trust me in that if I can wire an 11 wire SMT-6 and tune it with no instructions, or help (and I'm the only one on earth anyone knows of woot!). You guys can cut one wire and solder a dial in.

I suggest looking in whatever manual you have. Toyota, Lexus, Hayes, Chilton. Don't count one book out. They're all equally incorrect on ECU wiring, simply because the wiring can change on what seems like a random basis from one day to another.

Just find the ECT marking on the diagram, and look at which wire it's on.


This is how tuning should proceed.

Obviously everyone's potentiometer will adjust at a different rate. Start with the potentiometer turned off 0-resistance. Crank the car. Then turn the knob slowly until your RPM rasises in 100rpm increments.

The greatest performance increase should be with your idle raises somewhere between 950rpm and 1100rpm. Most will probably split the gains between 1000rpm-1050rpm.


This isn't going to give you a huge amount of power. What it will do is advance the timing between .5 and 2 degrees, and add 2-4% extra fuel to the injectors.

It's not much, but we're talking a $2-$3 part and less than 15 min of work.


The engine reporting a lower than normal temp will not affect the engine's ability to shift the transmission, or rev freely. In the unlikely event you bought the wrong resistance potentiometer and it happens... Turn the dial the other way, or get a 500 ohm potentiometer!


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