I saw some postings and some mentions but not too much on IAT resistors. Almost everytthing on the net is about more power not fuel economy. I apologize if this has been beat to death years ago.
I just went for the gold. I put in the lowest resistance that the computer would accept without setting a code for Intake Air Temp out of range and compared that with a 10k resister. Here is a little range of experiments and the intake temp I see on the Scangauge. I just used the nominal values of the resistors rather than measuring them. A co-worker tried to tell me about these "chips" a year ago or so and I just totally discounted it. This is darn near the stuff of urban legends. These resistors are 99 cents for a pack of five at Radio Shack. I have never done so much so cheaply before in my life. This is on my 2001 Saturn SL.
10k ohm IAT 28 F
940 ohm IAT 198F
136 ohm IAT 233 F this is two 68 resistors in series.
068 ohm IAT 279 F set an out of range code.
I did an ABAB experiment on the same 8.5 mile loop trying to drive identically. The lights did not cooperate 100% but I judge the experiment valid. The two runs with the 10k ohms were 43.3 and 44.1 mpg. The two runs with the 136 ohms were 61.0 and 63.9 mpg. The average speeds ranged from 29-31 mph. The difference between the average mpg's is 18.75 mpg giving an increase of 43%. The 10k ohm resistor was a slight handicap as the actual temp was 40 F. It was not far off since when I filled up yesterday my tank average was 46.2 mpg and this is just a little better than the 43.7 average of the two 10k runs.
Average difference 18.75 mpg or 43% using the 10k ohm mileage as the base.
I then went out on the freeway and made a 16 mile total loop at 60 mph and got over 60 mpg without any engine off coasting. I just drove easy. I did a bit of idle coasting on the last bit coming home as I could see the average was at 59 and wanted to break 60 mpg.
This morning I did the trip to work starting with a cold engine, I did not need to go to work it is just a familiar route. Against the slight grade and more than slight wind I made 53.8 mpg to work on the freeway at 61 mph. There was no drafting. The instantaneous mileage was between 55 and 60 mpg. I never shut off the engine but reset the current trip at work and started home. I came home on secondary roads so I could drive slower and pulse and glide with the wind to my back. By the time I got to near 1/2 way home my average was 112 mpg. I then lost a bit on as the lights would not turn green until I triggered them myself in the light Sunday morning traffic. I had to get into 2nd gear at several lights. At the stop sign at one road I botched the takeoff and lost about a mile per gallon. I only mention this because the trip home averaged 99.6 mpg. Darn it all anyway. The round trip averaged 70 mpg at an average speed of 40 mph. Here is the "today" summary:
40 mph ave
My car obviously has a sensor that tells it when I am in fifth gear. The instantaneous mileage makes a distinct jump now when I hit fifth gear. Something beyond the usual expected with a shift. I can accelerate decently on a slight upgrade at 40 mph in 5th gear and get 50-60 mpg during the acceleration. This does more than just adjust the timing. I can watch the timing and while it changes some with the resistor the change is not that great and something else is going on. Some think it leans the engine out but it is running closed loop. My current theory suggests EGR. I have run engines lean and ruined one turbo 2.3 Ford engine running it lean. This does not feel lean. Drivability is not suffering in the least. I am excessively short shifting to get into fifth gear as soon as I can because I see the immediate benefit.
The only aero mods to my car are blocking the grill and removing the spoiler. I have not even proven that removing the spoiler is a good thing.
This is pretty unbelievable. Nothing will be really confirmed until more distance passes and I have to fill up and check the calibration again on the Scangauge. Last check was within 0.5% yesterday. I hope this is for real. It sure looks that way. I suspect that the exhaust temp is probably not warm enough to keep the catalytic converters on line. Just speculation at this point.
If someone else was writing this I would not believe it either.
Sorry about putting this out three times and twice in the wrong place. I hit some control key and jumped thread without realizing it and don't know how to remove this thread once started.
Thanks for making a new thread on this. I keep imagining a "clicking dial" on my dashboard that goes from "off" to different resistor settings that mess with the IAT input. Different cars can have different resistors. I don't think a potentiometer would work because the resistance range is too great (right?).
1 - For car ECU/PCMs that like this mod, I think it makes a big difference. I also think that, if possible, it would be nice to know what the emissions are. For the purpose of an experiment, anything goes, but I also want to know the long term effects are on the emissions.
2 - You'll burn your valves out! Ha ha ! This is the "A Christmas Story" argument, aka "you'll shoot your eyes out!". How is you engine doing? Can you gauge the engine temperature with and without the mod? Since we are "driving gentle" I don't think the engine is at risk, but I would like to know that the long term effects are on the car and what the "danger zone" is.
It is true that lean running stresses the exhaust valves and can ruin them if it is done to excess. Airplanes use exhaust gas temp gauges and the pilot adjusts mixture strength accordingly.
Does this sound like a legitimate test (I can't find the URL where I read this!!!)? I think it sounds inline with what you just wrote because it is related to exhaust gas temps :
1 - Get a high temperature thermometer that is rated to about 1000 degrees.
2 - Install it post catalytic converter. EDIT : INSTALL IN EXHAUST HEADER, NOT POST CAT
3 - Run the car as normal without the IAT mod.
4 - Run the car with the mod.
In step 4 you *should* see the temperature increase as compared to step 3. If the temperature increases 180 degrees F over the temperatures in step 3, then you are in danger of damaging your catalytic converter (EDIT : YOUR ENGINE, NOT YOUR CAT). For me, that would mean shooting for a "safe" maximum of 100 degrees F over step 3.
EGTs (exhaust gas temps) are usually measured right on the headers, usually the 3rd (I think) on a honda, because the firing order causes the third to be the hottest, or something such. I would think the cat would mess up and accurate temp readings, at least in reference to engine performance.