IAT resistor

[Grashwi]

I'm going to install a resistor on my Input Air Temp sensor that basically tells the computer that the incoming air is slightly cooler than it really is causing the computer to 'richen' the fuel mix. Here's why. In southeast Wisconsin we can only buy reformulated gas to help with air quality. Along with the 10% ethanol our gas has an additional additive (MTBE?). This has a noticeable negative affect on both MPG and performance. I can even tell the difference in my lawn mower! Now, when I travel up north and come back with unreformulated gas I get significantly better mileage and performance back on my normal commute. Around 51 normally and around 55 with the good stuff. This tells me that the fuel mix, probably biased around emmissions, is costing me performance/mpg. I'll need some time to evaluate whether it makes a difference but I though I'd troll a thread to see if anyone else has experience here. I'm going with the MindBlower chip instead of trying to craft something myself.
Grant

[kohnen]

Don't bother - the computer will eventually catch on.

The reason for the IAT is so that the computer can figure out how much fuel to use when you quickly open the throttle. But, the computer monitors the oxygen sensor to determine what the precise air to fuel ratio needs to be. It then uses that calibration information to change how much fuel it puts in when you blip the throttle.

In addition, you don't want your engine running rich. That means that you are dumping unburned fuel into your cat converter. The cat converter, in burning that fuel, will overheat and become damaged.

[tesla440]

By fooling the AIT sensor, It will make the car run richer. I dought that it will cause a catalytic converter faulure, since the O2 sensor will correct the issue. But what might work would be getting warmer air from the radiator area into the intake. Warmer air needs less fuel to burn at the right mixture. Ofcourse you will have less engine preformance, but the prius has an electric motor to make up for any noticable deficiencies.

[kohnen]

Originally Posted by tesla440

By fooling the AIT sensor, It will make the car run richer. I dought that it will cause a catalytic converter faulure, since the O2 sensor will correct the issue.

The computer will correct the issue by leaning out the mixture.

The O2 sensor will tell the computer that there isn't any oxygen in the exhaust. The computer will compensate by leaning out the mixture (either by opening the throttle plate more, or by reducing the amount of fuel injected). Either way, the air to fuel ratio will ultimately be set to the same stoichiometric ratio of about 14.7.

Air-fuel ratio - Wikipedia, the free encyclopedia

[BT Tech]

This is absolutely correct. In fact, when I had my Prius on our chassis dyno, I connected out wideband 02 sensor and found that the car actually ran at a leaner than normal 15:1 A/F ratio than the normal 14.7.

As this poster already pointed out, modern day engine computers are a lot smarter than people give them credit for. Even if you install a resistor of a set value for the IAT, the 02 sensor will instanlty see the resulting richer fuel mixture and reduce the duty cycles to the injectors so that it maintains its pre-programmed A/F ratio.

In other words, don't bother....

Originally Posted by kohnen

The computer will correct the issue by leaning out the mixture.

The O2 sensor will tell the computer that there isn't any oxygen in the exhaust. The computer will compensate by leaning out the mixture (either by opening the throttle plate more, or by reducing the amount of fuel injected). Either way, the air to fuel ratio will ultimately be set to the same stoichiometric ratio of about 14.7.

Air-fuel ratio - Wikipedia, the free encyclopedia

[Grashwi]

Perhaps and thanks for the insight. I'm still interested in mitigating the affect of the reformulated gas that we have here. If you are saying that the oxygen sensor will override the input from the IAT then perhaps it's beyond my control. Since I already bought it, and it's removeable, I'm going to install and see what affect it has. I'm hoping my IAT has at least as much 'weight' as the oxygen sensor, else why have it? Must be part of the programming or it would be dead cost.

[Rokeby]

It seems some folks come at possible engine mods from the mechanical
perspective. Others come from the electronic angle. Different strokes...

Although I'm not in any way a mechanical type of guy, I'd like to offer some
random thoughts from reading posts here on PriusChat:

Instead of trying to trick the computer, it appears that you can lower the air
inlet temp by 2-4 deg F by piping around the throttle block heater. See these
threads:

tb coolant bypass modification results

TB Hot water bypass

At some point engine modders seem to get the urge to change the air intake
tract. It appears that the inlet tract is highly engineered and even small
changes make big differences -- I guess a Mini-Cooper S hood scoop is out of
the question. As a start, check here:

air intake pocket

Lastly, there are many folks looking into these sorts of things on other
forums. For a quick way to access them, use the search function, and then
choose the Google search option. Most likely you will find some threads on
Ecomodder.com. A very interesting group of max-MPG adherents, most
driving non-hybrids. Some amazing stuff here.

Enjoy!

************************************************** **************

[Edit] A Side Bar: The latter thread about the Prius air resontor raised this
question in my mind: What if you filled the resonator with ice cubes such that
the inlet air temp was significantly lower, say 10 Deg F, than the outside air
temp as shown on the MFD. Would the computer(s) use the intake and outside
temps separately or go into some kind of recursive loop trying to resolve the
differences?

[BT Tech]

Various inputs are "looked" at by the engine ECU such as IAT, ECT (Engine coolant temp) TPS (Throttle position) (MAF )Mass Air Flow, MAP (Manifold absolute Pressure) and a host of other inputs to calculate the correct A/F ratio and ignition timing at any given moment.

When you first start the engine when cold, the system is in "open loop" where it reads these various sensors and matches the said values to a pre-programmed fuel and ignition map disregarding 02 sensor inputs. This is called the cold start value and having a colder or warmer ECT or IAT reading will determine the A/F ratio under the cold cranking mode and while in open loop.

When the engine warms up to a pre-determined point, then the system goes into "closed loop" where it predominately looks at the 02 sensor voltages and adjusts the duty cycle of the injectors to maintain its optimum A/F ratio and ignition timings for optimum effeciency. The other sensor inputs are used as well but the most critical value in determining the final fuel ratio is the 02 value. If the 02 sensor were to fail, the ECU would go back into a open loop status and read the values from the other sensors in an attempt to keep the A/F ratio correct.

Originally Posted by Grashwi

Perhaps and thanks for the insight. I'm still interested in mitigating the affect of the reformulated gas that we have here. If you are saying that the oxygen sensor will override the input from the IAT then perhaps it's beyond my control. Since I already bought it, and it's removeable, I'm going to install and see what affect it has. I'm hoping my IAT has at least as much 'weight' as the oxygen sensor, else why have it? Must be part of the programming or it would be dead cost.

[Grashwi]

Then perhaps I cannot improve on the air quality emphasis of the design. I'm happy with that unless I can trade a portion of air quality for mgp. I'll still try this since I'm not at all sure that anyone has really considered the poor efficiency we get from the reformulated gas we're forced to buy in SE WI. Might be interesting to see if a difference surfaces. To speak to one of the best informers here, I installed a BT stiffening plate on my 2008 touring. Hands down the amount of businessest of the wheel, compensating for wind buffet, is very much reduced. My wife is much more comfortable even, and she wasn't comfortable driving the upper 70s we do going up north. This one mod works in more extreme conditions and I'm hoping I can mitigate the affect of our gas too. If not, ya know, this ain't bad at all...
Grant

[V8Cobrakid]

so.. adding a hood scoop would be complete worthless.. and potentially loud?... or potentially damaging? (i've always been curious)