Robb235

Back when I owned my '97 4Runner (before some idiot smashed into it in a parking lot) I ran across the ECT mod, and liking the idea of being able to bump up timing slightly, I installed it. The idea is that by installing a variable resistor, you can fool the ECU into thinking that the engine is colder than what it actually is. With the engine being cooler, theoritically the engine will advance timing and also inject a little bit more fuel for an increase in power. Instructions can be found http://www.midiwall.com/4Runner/ect.html and https://www.yotatech.com/forums/f130...ect-mod-75163/

The author of this mod "proves" that this works by showing before and after pictures of engine data, where by having the mod dialed in, the short term fuel trims (STFT's) are slightly higher.

This is all garbage.

First, anyone who's ever put a scan tool on their vehicle and looked at the STFT's can see that the STFT's are constantly bouncing around. Even when the vehicle is not moving and is just idling in the driveway, the STFT's are constantly changing. When I had this mod on my '97, the STFT's bounced around between positive and negative just as much as when the mod wasn't in place. In fact, I don't even think the STFT's are what you should be looking at, you should be looking at the Long Term Fuel Trims.

I've taken my 4Runner on the highway (tried different speeds from 50 to 80) and my LTFT's aren't any different than when the mod is zero'd out (ie. back to stock). I also noticed that there is no difference in timing advance either.

The author claims a "seat of the pants" increase, and claims this is caused by more fuel and an increase in timing. However, I have an alternate explanation. Several years ago I owned a '95 Chevy Monte Carlo that sprung a small vacuum leak one day as I was sitting in traffic. A small vacuum line had popped off and my idle speed went from ~700 RPMs to around `1,500 RPMs. The cool thing about this was that the car "felt" like it had more power when pulling away from stop lights. Did the car actually have more power? No. But the vacuum leak was raising the engine speed making it feel like it did when I was barely touching the gas pedal.

The same thing is happening with the ECT mod. However, instead of a vacuum leak, the modified ECT signal is causing the ECU to open up the Idle Air Control Valve more, raising idle speed. You're not getting more power out of the engine. You're just pressing the gas pedal a little bit more in a round about sort of way. Want the exact same effect that this mod produces, but without splicing in a variable resistor? Press the gas pedal a little more.

These are just my observations. Feel free to discuss.

Inferno451

Interesting, good to see some smart diagnostics!

Texas_Ace

Makes sense, I have watched my wideband during startup and noticed that my AFR's are still ~14.7 even bone cold. I don't notice any difference in the AFR's during driving either.

So I do think we can rule out fueling as a possible reason. Short or long term trims are not how you gauge this anyways.

Timing on the other hand is possible, I did some minor datalogging on this but the data was inconclusive.

What I do know is that my truck has more power when cold, most likely this is due to it being cold and everything not being heat soaked. I go WOT basically every chance I get. While I don't generally do this before it is warmed up I have done it for testing in the past and noticed that the tires lit up easier/faster when cold.