IAT Sensor Mod Experiment

[davidjh72]

IAT mod rules! I've been averaging 34 MPG per tank previously. 41.1 MPG tank today with the IAT mod done midway through this tank of gas!

I unplugged the IAT sensor and put two 1/4-watt "470-ohm" resistors paralleled into the IAT connector. Scangauge reports IAT 198F. Car drives the same as before, though I keep RPM's below 3500 just to be safe. Ignition timing is the same so there doesn't appear to be any compensation of the timing by the ECU because of the high IAT temp reading. With the engine running leaner now (less consumption), I'm not going to put the engine under and undue strain. Shifting at 2500 RPM. Driving for enconomy!

I found that a 4700-ohm resistor sets IAT to 55F. Perfect for the 47F temp today. IAT is 5 to 10 degrees warmer than ambient temp at-speed anyway. Saves unnecessary disconnect/reconnect of the IAT sensor in A-B-A testing. One resistor for "normal", the other for "super MPG". I need to put in a switch so I can select low/high resistor. IAT 55F, MPG dropped to the high 30's. Set the IAT back to 198F with the 230 resistance and MPG jump to the high 40's, even 52 MPG.

I'll check the spark plugs after a few days to check for signs of "severe lean-burn"

Yesterday, Today, and Current Trip reporting with ScangaugeII...
http://s139.photobucket.com/albums/q...-IAT-52MPG.flv

[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!

[repete86]

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!

[diamondlarry]

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!

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.

[rockouthippie]

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

[Bill in Houston]

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.

[Jim Dunlop]

Why not just remove the IAT from the airbox/intake and move it closer to the engine?

[Lug_Nut]

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

[Snax]

This page illustrates the output behavior of a wideband sensor, and that would be the place to start if you want to start hacking signals on an OBDII car. A simple adjustable voltage divider would allow tuning how the compter responds.

[cheapybob]

this is the same stuff I did a year ago. best economy i can get is with actual intake air temp about 160 (preheated intake) and resistance set for 242 degrees IAT. I had to use a switch because although these settings improved fuel economy by about 15% on the road, they make it hard to start when cold.