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Old 02-25-2007, 11:07 AM   #1
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Intake Air Temp resistor experiment.

My Intake Air Temperature resistor EXP

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Intake Air Temp resistor experiments
Copied from general discussion.

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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.

Summary
136 ohm 61.0 mpg
10k ohm 43.3 mpg
136 ohm 63.9 mpg
10k ohm 44.1 mpg

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:
70 mpg
40 mph ave
63 max
28.7 miles

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.

Ernie
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Old 02-25-2007, 02:43 PM   #2
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Nice report

Quote:
Originally Posted by usedgeo
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.
So what do you think EGR is doing? It was my understanding that by making the ECU think its inhaling an inferno it will use less fuel at the cost of power. But you are saying that its not driving noticeably different?
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Old 02-25-2007, 03:32 PM   #3
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Quote:
Originally Posted by Red View Post
Nice report

So what do you think EGR is doing? It was my understanding that by making the ECU think its inhaling an inferno it will use less fuel at the cost of power. But you are saying that its not driving noticeably different?
I would not say I that I am not losing power. I really haven't used hard acceleration lately. I meant to say that it is running very smoothly with no bucking or hint of a lean condition. This was just beyond my wildest expectations.

With respect to the EGR it is partly used to limit detonation and control peak combustion temperature. When the engine is fed very hot air both of these will increase. I think the EGR ratio is increasing and this is lowering the throttle loss. The only instruments I have that could give a verdict on this are the TPS and MAP sensors. It was just too much to watch in my excitement.

Ernie
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Old 02-25-2007, 03:47 PM   #4
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I've been meaning to do this, but I'm not sure of exactly how to perform this modification. I'm pretty useless under the hood. I couldn't even find the IAT sensor under the hood. What exactly should I be looking for?
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Old 02-25-2007, 03:56 PM   #5
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You would be looking for a connector on the tube that let's air into the air cleaner box. I suppose that some manufacturers may put an IAT after the aircleaner but, on my Saturn, it's near the end of the tube that extends outside of the engine compartment.
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Old 02-25-2007, 04:01 PM   #6
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IAT sensor

[QUOTE=What exactly should I be looking for?[/QUOTE]
It is a small connector on the other side of the aircleaner from the pipe to the manifold. It is down about 3 inches below the cross stucture just to the front of the air cleaner. You can just reach it. I chose to pull the aircleaner assemble to get my hands on the wires. There were three 10mm headed bolts holding the air cleaner in on my car. Here are some excellent instructions. These are just for a different purpose and a different car but the principle is the same.

http://kingenterprises.net/IAT-Timing-Tricker.htm


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Old 02-25-2007, 04:04 PM   #7
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Thanks alot!
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Old 02-25-2007, 05:40 PM   #8
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I gotta believe that you are forcing an extra lean condition that the O2 sensor feelback can not compensate for and are producing a lot more NO2 emissions as a result. Pretty impressive results however.
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Old 02-25-2007, 06:30 PM   #9
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That's interesting. That's been discussed here before and it seems to work with the Saturns but not with those kinds of results. I wonder if you have something else going on with the engine. Maybe pull the plugs after a few more trips to see what they look like. You have hit the mother load . Keep us posted.
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Old 02-25-2007, 07:11 PM   #10
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Too bad the SG doesn't show short/long term fuel trim - that would answer some questions.

JanGeo: if the O2 sensor wasn't able to correct for a lean condition, I'm pretty sure it would throw a code, wouldn't it?
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