 GasSavers_Explorer Resistance 03-27-2006, 07:14 AM
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10-05-2005, 09:13 PM
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#1
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Registered Member
Join Date: Sep 2005
Posts: 144
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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.
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<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.
__________________
Scouring the country for an excellent condition Civic VX
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03-20-2007, 10:41 AM
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#2
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Supporting Member
Join Date: Dec 2006
Posts: 107
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3-15-07
So much for improving MPG with the IAT resistor mod. ScanGauge under-reported gas usage at 7.0 gallons, a whopping 1.465 gallon error. While SG showed 44.3 MPG, I actually got only 36.50. So I've put the IAT sensor back in place.
3-19-07
64 mile commute to work each way. 36 miles country roads, stopping at regularly spaced stop signs every 4 to 5 miles. 26 miles @60 MPH freeway. 65 MPH max. With IAT un-modded, I get the usual MPG and closer reporting of the ScanGaugeII to the actual gallons used. SG reported 9.6 gallons used (35.5 MPG). FE about the same as the last tank, IAT-modded. Proves that at least with my Saturn, tricking the ECU into thinking the engine is breathing hotter air that it actually is, only affects my SG to make me think I'm getting way better FE, until I gas up. SG honest with an un-modded car. Trick it out, and SG tricks the owner!
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03-20-2007, 04:00 PM
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#3
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FE nut
Join Date: Sep 2005
Posts: 1,020
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Quote:
Originally Posted by davidjh72
3-15-07
So much for improving MPG with the IAT resistor mod. ScanGauge under-reported gas usage at 7.0 gallons, a whopping 1.465 gallon error. While SG showed 44.3 MPG, I actually got only 36.50. So I've put the IAT sensor back in place.
3-19-07
64 mile commute to work each way. 36 miles country roads, stopping at regularly spaced stop signs every 4 to 5 miles. 26 miles @60 MPH freeway. 65 MPH max. With IAT un-modded, I get the usual MPG and closer reporting of the ScanGaugeII to the actual gallons used. SG reported 9.6 gallons used (35.5 MPG). FE about the same as the last tank, IAT-modded. Proves that at least with my Saturn, tricking the ECU into thinking the engine is breathing hotter air that it actually is, only affects my SG to make me think I'm getting way better FE, until I gas up. SG honest with an un-modded car. Trick it out, and SG tricks the owner!
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I think that once the Team Challenge is over that I may return my IAT back to stock to test this on my car. I'm getting great mileage now and I would hate to jeapordize that.
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Horsepower is how hard you hit the wall, torque is how much of the wall you take with you.
2007 Prius,

Team Slow Burn
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04-07-2007, 01:08 AM
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#4
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Registered Member
Join Date: Apr 2007
Posts: 1
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This isn't gonna work for most cars. If you have a O2 sensor, the computer probably will override your new mixture settings. This sounds a lot like an oxygen sensor mod I did on a Eagle Talon. It would go like raped batsh*t, but running that rich screwed up the cat converter. It got 12mpg city, but I didn't care.
That's the whole point of this system. To keep the cat converter from getting unburned gas through it. Clogs em up tighter than a drum. 2 cat converters in 3 years taught me the error of my ways.
I think if I was gonna try this, I'd make sure it had a switch for overriding it most of the time. This would give you control over your fuel mixture, if the O2 sensor doesn't override your trickery.
So, if I figure this right, you could either rich the engine out or lean it out with this trick. Being too lean will burn valves. Being too rich will clog the cat converter up. Neither is going to pass DEQ.
If you guys want to really beef up your fuel injected stock rods, you should use a bigger throttle body. It's pretty much "bolt on" 25 hp. I got an aftermarket one for my Lincoln for $200.
Kevin
retrovision.tv
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03-20-2007, 03:45 PM
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#5
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Registered Member
Join Date: Nov 2006
Posts: 358
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When I tried it in my Accord, it murdered my FE. FE dropped to almost 30 mpg at 55 on the highway, which is about what I used to be getting at 80 mph with the AC on!
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04-07-2007, 03:23 AM
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#6
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Registered Member
Join Date: Mar 2007
Posts: 1,138
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I think I know what you are saying as far as the O2 sensor and closed loop mixture control. However, I think that the thought is that some ECUs will allow a leaner condition at some IATs than at others. For example, my ECU might say it's okay to run lean when the IAT is 80 deg, but not when it's 30 deg. So on a 30 deg day, the mod gets me to a lean-burn condition that I would not have otherwise been able to achieve.
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05-24-2007, 03:13 AM
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#7
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Registered Member
Join Date: May 2007
Posts: 125
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Why not just remove the IAT from the airbox/intake and move it closer to the engine?
__________________

Team: Right Lane Rollers
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05-26-2011, 03:49 AM
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#8
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Registered Member
Join Date: May 2011
Posts: 1
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Re: IAT Sensor Mod Experiment
Quote:
Originally Posted by Jim Dunlop
Why not just remove the IAT from the airbox/intake and move it closer to the engine?
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because you a MIL and it reads -40F if you do.
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05-26-2011, 06:39 AM
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#9
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Site Team / Moderator
Join Date: Sep 2008
Location: Northern Virginia
Posts: 4,744
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Re: IAT Sensor Mod Experiment
Quote:
Originally Posted by happybobcat
because you a MIL and it reads -40F if you do.
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Huh?
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05-24-2007, 04:34 PM
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#10
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Registered Member
Join Date: Oct 2006
Posts: 557
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The VW TDI diesels apparently respond to increased resistance (colder apparent temperatures) by advancing the initial injection. These are direct injection engines with the fuel injected into the combustion chamber at or very near to TDC, not duty cycle dependent injectors spritzing into the intake tract before the intake valve. This difference (injection timing vs. duty cycle) may be why the colder apparent reading in the TDI is desired for improved mpg, rather than warmer temps for gassers. This TDI version was developed from owners of converted TDI running on heated veg oil discovering a reduction in fuel economy related to retarded injection timing as the waste fat fuel heated up.
I'm still not entirely sold on the idea, although for the admission price of a pack of five resistors, it's a cheap experiment. I'll post if I think it's worthwhile after a suitable trial phase.
Details on the TDI "FAT" Fuel and Air Temperature mod, also known as "KFC" Kerma's Fuel Cooler can be found by using the search feature at www.TDIClub.com
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