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Old 10-05-2005, 10:13 PM   #1
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IAT Sensor Mod Experiment

This experiment is for the IAT sensor mod in which the signal from the IAT sensor is bypassed with a fixed value resistor. The value of the resistor is chosen such that the ECU reads a temperature hotter than the IAT sensor is reporting.

The theory: Fuel mix is determined by a very large number of factors and is directly controlled by the length of time the fuel injectors stay open. Each factor is supplied to the ECU through all the engine's sensors. The ECU then takes each value to a lookup table which will return a constant multiplier for a given input. For example, if a lean condition is detected from the oxygen sensor, the multiplier will be greater than 1, resulting in a richer mix next cycle. The same thing goes for the intake air temperature. If the sensor is reading a hot temperature (hotter than normal) then the lookup table for the IAT sensor will report a multiplier less than 1. By tricking the ECU into thinking it's always reading a very hot temperature from the intake, the ECU can be forced to reduce the length of the pulse controlling the fuel injector by manipulating one of the many factors controlling fuel mix.

I used the same resistors SVOBoy showed. The two 220 Ohm resistors measured 107.8 Ohms in parallel. This should produce a reading of approximately 240 to 250 degrees F. The coolant temp gauge read the same temp as before the mod. It does not appear that the leaning effects of this mod has enough effect to overheat the engine.
<br>
<table border="5" cellpadding="5">
<tr>
<th colspan="2">
<b>10/5/05 - IAT Sensor Mod Trial #1</b>
</th>
</tr>
<tr>
<td>Fuel economy:</td>
<td>35.3 mpg</td>
</tr>
<tr>
<td>Previous fuel economy:</td>
<td>34.0 mpg</td>
</tr>
<tr>
<td>Percent difference:</td>
<td>+3.82%</td>
</tr>
<tr>
<td>Trip:</td>
<td>79.35 miles</td>
</tr>
<tr>
<td>Fuel used:</td>
<td>2.245 gallons</td>
</tr>
<tr>
<td>Fuel grade:</td>
<td>Shell V-Power 93 octane</td>
</tr>
<tr>
<td>Driving type:</td>
<td>Highway</td>
</tr>
<tr>
<td>Target speed:</td>
<td>65 mph</td>
</tr>
<tr>
<td>Tire pressure:</td>
<td>40 psi</td>
</tr>
<tr>
<td>Temperature:</td>
<td>79 degrees</td>
</tr>
</table>
<br>

The previous fuel economy used was from Trial #4 of the tire pressure experiment. I'm averaging the temperatures for the trip there and back to get 79 degrees, which was tonight's temperature.

I don't know if I'll do any more trials because I really want to get started on acetone. It is possible that Honda uses different resistences for temperatures than other manufacturers. I'll try and research this to see if another trial is worthwhile.

Everyone else conducting this experiment, please post your results.
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Old 10-05-2005, 10:19 PM   #2
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Can you post exactly how to

Can you post exactly how to make this so I can make one? Including part numbers or schematics if possible.
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Old 10-05-2005, 10:33 PM   #3
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Well it's pretty easy. Go

Well it's pretty easy. Go to Radio Shack and buy a pack of 220 Ohm resistors for $0.99. Take two resistors, place them side by side, and twist the leads together. Refer to SVOBoy's picture for exactly what it should look like. Next find the IAT sensor for your engine. Mine was sitting right on top of the intake maifold in a black plastic box. There should be a two wire connector coming out of the sensor. Remove the connector and stick the ends of the resistors into the female plug. Wrap some electrical tape around everything and you're done.

Twisting the resistors together in parallel will make the total resistence lower than the individual resistences.

1 / TotalResistance = (1 / R1) + (1 / R2)

For R1 = R2, total resistance equals R1 / 2. In this case, two 220 Ohm resistors in parallel would yeild a net resistance of 110 Ohms.
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Old 10-05-2005, 10:39 PM   #4
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Very cool This will be on my

Very cool

This will be on my list of things to test when my acetone test is done.

I have a few questions, but I'll address them elsewhere and leave this for posting results.
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Old 10-06-2005, 11:42 AM   #5
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Concerns

My only concerns with this that I think are worth mentioning here is that I think flatland should've figured out the resistance crap for honda, because I'm almost sure that honda will use different ratings than saturn. When I get my hands on a multimeter tomorrow I hope then I will measure the resistance across my sensor at like 70 degrees, and then mehbe try to boil it and measure the resistance at like 200 degrees. I think that if flatland only got that much increase that the resistance wasn't changing it to 240 degrees, but mehbe like 120 degrees or something. I dunno though, that resistance needs to be figured out.
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Old 10-06-2005, 11:52 AM   #6
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Re: Concerns

Quote:
Originally Posted by SVOboy
My only concerns with this that I think are worth mentioning here is that I think flatland should've figured out the resistance crap for honda, because I'm almost sure that honda will use different ratings than saturn. When I get my hands on a multimeter tomorrow I hope then I will measure the resistance across my sensor at like 70 degrees, and then mehbe try to boil it and measure the resistance at like 200 degrees. I think that if flatland only got that much increase that the resistance wasn't changing it to 240 degrees, but mehbe like 120 degrees or something. I dunno though, that resistance needs to be figured out.
I'm fairly certain this information would be in the service manuals. Perhaps one of us can track one down and try to get the needed info.
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Old 10-06-2005, 12:17 PM   #7
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I have a saturn. So I will

I have a saturn. So I will probally do this when i have the time.
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Old 10-06-2005, 02:46 PM   #8
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Honda information

I looked up the IAT part of the 88-91 manual and the closest it said was measure it and if it was from 1k-4k ohms it was still good. This seems way high, especially considering flatland got an improvement with 110 ohms. I guess it'll just take testing.
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Old 10-06-2005, 09:03 PM   #9
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I'm guessing the 1k to 4k

I'm guessing the 1k to 4k thing is for checking when cold. That should cover temperatures from about 10 degrees F to 100 degrees F according to a chart I have (although I think it's for Toyota's). I'd imagine that the resistences used are pretty standard for these sensors.

I might go outside in a little bit and measure the sensor when cold, then get it up to operating temp and see what it gives.
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Old 10-06-2005, 09:33 PM   #10
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Re: I'm guessing the 1k to 4k

Quote:
Originally Posted by Flatland2D
I'm guessing the 1k to 4k thing is for checking when cold. That should cover temperatures from about 10 degrees F to 100 degrees F according to a chart I have (although I think it's for Toyota's). I'd imagine that the resistences used are pretty standard for these sensors.

I might go outside in a little bit and measure the sensor when cold, then get it up to operating temp and see what it gives.
I'm guessing you could actually hook up the multimeter to your IAT and then drive around for a while and see what it says. Put the multimeter in your car and run the wires through the firewall to see what the resistance is.

But then again, finding a suitable shop manual might be better.
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