IAT

[Special Ross]

I heard that if you unplug the IAT sensor and run premium gas, you will gain more power and run faster. I think my buddy told me he looked up his IAT temp with the sensor unplugged and it was at -40 degrees. Does anyone know when the computer thinks its that cold how much it advances timing? Would that "hurt" the engine in any way?

Thanks

[GrandAmGT99]

Courtesy of 60 Degree V6
http://www.60degreev6.com/index.php?p=pages&pid=18


IAT stands for Intake Air Temperature. It is a simple thermistor that changes its resistance according to the temperature it is at. The idea beind this modification, is that by changing the resistance to that of a cooler interpreted reading, you will get more fuel. While it is true that you will dump more fuel...its false that this is a good idea. Running rich is bad for performance, so you are just wasting your time with adding more fuel in this fashion.

The stock computer already compensates fuel as it is, so trying to trick it into giving you more fuel is completely worthless. If you dump too much fuel, via switching to a colder resistance on the IAT while driving, you may even notice a puff of black smoke out the exhaust. Then, the O2 sensor will detect the overly rich mixture, and reduce the injector pulse width. This totally defeats the purpose or the IAT mod.

[lrymal]

Go here for another viewpoint:

http://www.grandamgt.com/forum/showthread.php?s=&threadid=198&highlight=iat

Personal experience, for what that is worth, is that it helps for partial throttle acceleration only, giving a "crisper" feel of the accelerator. According to the tech manual, colder temperatures will cause a higher resistance on the sensor, which in turn will cause a bit of a timing advance. There really isn't that EXTREME of a fuel dumping, or so the manual sez.

You won't get full throttle rocket launch benefits. I have played with the IAT mods for about 60K miles, from relocation to bridging the sensor with approximately a 2K ohm resistor. Any higher resistance hammers the computer brain too much, at least on my car. For reference, the sensor's resistance increases with lower temperature, and decreases rapidly during summer temperatures.

I would think (opinion only and from dealing with my car), that the practical way would be for the resistor to be used during hot summer, and use a RELOCATED sensor to the front intake by the headlamp during the winter and rig a simple switch to go between the two.

The relocation idea is a good compromise and gets the sensor closer to the air, rather than having it in an environment that soaks up internal engine bay heat, especially when the car is sitting in traffic. But, the problem with the relocation idea is that summer time road surface heat can be bothersome also, thus nearly defeating the relocation idea. BUMMER! Sooooo, the resistor idea sounds good again since the sensor is not active when the resistor is used.

Both methods have their merits.

So, I have used exclusively the 2K ohm resistor, but the idea of seasonal SWITCHING between the relocated sensor and the resistor is compelling. A simple switch could flip from the relocated sensor to the resistor. A problem with a switch is that the car's computer will take a few minutes to accept the new value readings. You wouldn't just flip back-and-forth, back-and-forth.

And I know what the internet sites say about the IAT mods. The resistor idea, in theory, when working with the car's emissions and mixture brain, just doesn't sound like a good idea. It does indeed seem VERY contradictory in the theory but for me. But for me, it works judged not by sound, but by the crisp feel at the accelerator pedal.

My Grand Am has high mileage and there is no carbon or indicator of richness when the plugs were pulled for replacement. Plus the car passes all the tailpipe and computer emission tests. And gasoline tank mileage has always been 270 to 330 in town, nearly 380 to 420 on the highway.

Anyway, that is what has happened with my car. I'd say give it a try for a month, keep the resistor's value slightly lower than what the mod sites say. If you don't like the change, it is VERY simple to put everything back.

[GrandAmGT99]

Good explanation...it's always good to have a healthy argument. I have not done this mod, and don't plan on it, so I can't give you a personal POV, but i was more convinced with the "Don't
Do It" argument...Either way, it's great to see these things being posted again.

[lrymal]

Originally posted by GrandAmGT99
....I have not done this mod, and don't plan on it, so I can't give you a personal POV, but i was more convinced with the "Don't
Do It" argument...
Actually, I was convinced not to go with it but had this nagging issue with the car's in-town acceleration (just normal traffic) during hot weather. And it was irritating because during winter time, the car really zinged in city traffic.

For me, the feeling was like a car from a couple of decades past that didn't have its vacuum hose line attached to the distributor. Therefore, the car was consistantly retarded on its timing during acceleration. Reattaching the vacuum advance hose would restore timing advance which would occur on acceleration. That honestly is the feel that I had.

Soooo, I played with IAT relocation which really worked nicely, but the car became sluggish on hot city roads during the summer since the intake was sucking in hot road surface air.

In comes the dreaded resistor mod. There are so many arguments, pro and con, all seemingly good in their discussion. Anyway, I played with various resistor values and for my car, the 2.2K ohm resistor was the happy value. The two most accepted values are 3.3K ohm and 4.6K ohm. Those are just too extreme and I *think* (pure speculation) they advance the timing too much during city-acceleration. The knock sensor probably goes on the attack since there is probably detonation at those resistor's values and lowers the timing, thus defeating the modification. Still just guessing.

But at about 1K ohm to 2.5 or less, there really seems to be a crisp feel to city-acceleration and the feel is like what you get during winter time acceleration. I don't detect any real full-throttle benefit. The car feels "peppy".

This certainly has worked for me for all these thousands of miles.
Either way, it's great to see these things being posted again.
And I agree, pro and con discussions are healthy and good. Lots of issues can come up which flushes out the facts and truths.

Sorry about the lengthy replies. I really have run-of-the-mouth on the keyboard.

[Special Ross]

Well...I went to the track on wed. nite and I made a run with the IAT sensor plugged in, then on my second run I unplugged it and my SES light came on (expected) and I gained a tenth of a second. On my third run, I cleared the code in the staging lanes bumped up my psi on my back tires and made my run which was a tenth of a second slower than my second run and my MPH went up by 1 MPH too. BTW, right before my third run, they had to clean the track of syntheic oil spilled by someone. Could someone please enlighten me about this?

Thanks