IAT resistor hack - JeepForum.com
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post #1 of 34 Old 07-13-2019, 04:28 PM Thread Starter
BilletHorse
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IAT resistor hack

Decided to try the mythical IAT resistor hack that tricks the ECM into dialing in a little more timing by lying to it about the intake air temperature.
The claims are all over the place in the Internet, from a mere 1-2 MPG and a 5-10HP gain all the way up to 20-30HP (which I don't believe for a second!)

Went to the boneyard this morning and snagged an IAT sensor from a dead soldier plus the connector.

Cut off the thermistor and soldered on two wires to turn it into a plug.

Soldered in a 4.7k ohm resistor (the value most widely talked about) in line with the red wire.

Soldered on the connector, giving me essentially a removable pigtail to I can go back to factory if needed.

Fired up the Jeep and checked the IAT readings before and after the pigtail install.

Hopefully I will notice some results. Will be listening carefully for pinging!

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post #2 of 34 Old 07-13-2019, 04:43 PM
jtec
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do volunteer work with that extra time you have.
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 34 Old 07-13-2019, 04:48 PM Thread Starter
BilletHorse
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Quote:
Originally Posted by jtec View Post
do volunteer work with that extra time you have.
Ouch?

Was a quick deal, worth a little time if it works.

Should I not be posting stuff like this?
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post #4 of 34 Old 07-13-2019, 05:00 PM
Oktavius
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Quote:
Originally Posted by BilletHorse View Post
Ouch?

Was a quick deal, worth a little time if it works.

Should I not be posting stuff like this?
I'm curious in your results.
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post #5 of 34 Old 07-13-2019, 05:05 PM
jtec
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THINK - them puters be smart and getin more so each year..


I guess experimenting is in our blood.... gone are the days of a headers, holleys, and cams, its now programs sensors and inspections -

Google the term 'tuners' have fun
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #6 of 34 Old 07-13-2019, 05:33 PM Thread Starter
BilletHorse
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Quote:
Originally Posted by jtec View Post
THINK - them puters be smart and getin more so each year..


I guess experimenting is in our blood.... gone are the days of a headers, holleys, and cams, its now programs sensors and inspections -

Google the term 'tuners' have fun
The computer on my 2002 is 17 years old, that is barely Windows XP territory, mostly Windows 98.

This Jeep does not have a mass air flow sensor, so it doesn't have a direct way to determine the air density for spark timing, other than the MAP sensor. It uses the O2 sensor data to determine the fuel map in closed loop, so that can compensate.

When we run our older cars at this altitude we have to dial in a crazy amount of timing because it takes longer to burn fuel with less air.

I have been monitoring the ignition timing as I drive and logging, and have noticed that the computer is pulling way too much timing out for the conditions (again, altitude) therby making the engine less efficient and run hotter (a condition I wish to mitigate).

I will now be watching my timing curves and economy values to see if I have made progress. And then there is the butt dyno! <img src="https://www.jeepforum.com/ubb/smile.gif" border="0" alt="" title="Smilie" class="inlineimg" />
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post #7 of 34 Old 07-14-2019, 09:59 PM
DJTimyD
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Haters gonna hate...

Quote:
Originally Posted by Oktavius View Post
I'm curious in your results.
Me too. I guess I expected a more inviting environment here than you are getting Oktavius. I just bought an '04 WJ and I also live at altitude, and I have been looking at tips/tricks/mods to help with cooling, performance and efficiency. Ignore the jerks Oktavius - for every person who comments they are interested in something, there are 100 lurkers who are also interested but not saying anything. And for every grumpy-gus that casts aspersions... there are 3 other keyboard warriors just waiting to jump. May the odds be ever in your favor...
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post #8 of 34 Old 07-14-2019, 10:30 PM Thread Starter
BilletHorse
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I don't have any hard data yet, but seat of the pants, it feels a little more responsive, but I will know more tomorrow and will report.
I have a variable resistor, 10K coming Tuesday, I will wire that in and test to extremes. I would be willing to run premium if the economy gains are great enough to make up the price difference, or the fun coefficient is high enough!

I also turned the hydraulic fan solenoid screw in 1/2 turn but it didn't click, so I'm not sure if it help the setting.
More on that after testing also.

It was actually me who was taking some flack DJTimyD, but I don't mind. I love to experiment and try to improve my stuff!
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post #9 of 34 Old 07-15-2019, 10:51 AM
Jeeples
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Interesting...this has been around for a bit, particularly if you've ever poked around on some of the Dodge truck/SUV forums and results are mixed.

I wonder how this would compare to relocating the IAT to somewhere in the intake stream?

For those that are unaware, the IAT sensor on the 4.7 is mounted on the intake manifold. Where some folks find issue with this is due to heat soak, particularly when idling or startup after a short shut down.

Some folks will use the resistor trick and just let the harness dangle, such as the OP (with the stock sensor still installed), other will relocate the sensor to the airbox, resonator or the intake tube, claiming this to be a more accurate way to measure intake temp as you're forcing the engine to monitor actual incoming air temps vs. manifold temp.

I've been waffling back and forth on trying the relocation method, as it should help keep the sensor from getting that coating of blowback/oil gunk on it as seen in the OP.

His: '00 WJ 4.7 Limited- Some stuff

Hers: '03 WJ 4.7 Laredo- Some more stuff


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This is easily the worst post, and thread, I have ever seen in 7 years of being on JF.
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post #10 of 34 Old 07-15-2019, 08:26 PM Thread Starter
BilletHorse
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Quote:
Originally Posted by Jeeples View Post
Interesting...this has been around for a bit, particularly if you've ever poked around on some of the Dodge truck/SUV forums and results are mixed.

I wonder how this would compare to relocating the IAT to somewhere in the intake stream?

For those that are unaware, the IAT sensor on the 4.7 is mounted on the intake manifold. Where some folks find issue with this is due to heat soak, particularly when idling or startup after a short shut down.

Some folks will use the resistor trick and just let the harness dangle, such as the OP (with the stock sensor still installed), other will relocate the sensor to the airbox, resonator or the intake tube, claiming this to be a more accurate way to measure intake temp as you're forcing the engine to monitor actual incoming air temps vs. manifold temp.

I've been waffling back and forth on trying the relocation method, as it should help keep the sensor from getting that coating of blowback/oil gunk on it as seen in the OP.
I'm not letting the harness "dangle". I created a removable pigtail that will allow me to go completely back to stock if I want or need to. I made the pigtail a little longer than necessary because I knew I would be modifying it by adding a variable resistor (which came today). I tested the new variable resistor and although it is supposed to be 10k max, it is only 8.6k max, so I will leave the 4.7k ohm in line to get me to that 10k value.

Update: Today I was able to drive up the hill (Tijeras Canyon) in high gear without downshifting and not go any slower than the speed limit (65).
This is the first time I can remember ever being able to do that.
Certainly not a scientific result, but potentially significant nonetheless.

I need to do some controlled mileage tests with different resistance values, but I probably won't take the time. More likely I will solder in the POT and increase the resistance until it pings, then I will switch to premium and see.
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post #11 of 34 Old 07-15-2019, 08:55 PM
DJTimyD
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Quote:
Originally Posted by BilletHorse View Post
I need to do some controlled mileage tests with different resistance values, but I probably won't take the time. More likely I will solder in the POT and increase the resistance until it pings, then I will switch to premium and see.
I'm def interested in how this works w/o the switch to premium fuel... mostly because I'm cheap.

question/opinion: is this better, worse, indifferent to moving the IAT to the intake box? I'm down for either, just wondering which would be better and/or more accurate.
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post #12 of 34 Old 07-15-2019, 09:27 PM Thread Starter
BilletHorse
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Quote:
Originally Posted by DJTimyD View Post
I'm def interested in how this works w/o the switch to premium fuel... mostly because I'm cheap.

question/opinion: is this better, worse, indifferent to moving the IAT to the intake box? I'm down for either, just wondering which would be better and/or more accurate.
The main reason I did it this way was is because I wanted to be able to vary the OHM values.

I actually just got done soldering in the potentiometer and cranked it all the way, the computer was reading 50 degrees (ambient is 83) then started creeping up as the engine warmed. I am just going to "let it eat" in the morning and see what happens.
I'm foolhardy that way.
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post #13 of 34 Old 07-16-2019, 04:44 AM
Frambo
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This is awesome, keep posting updates!
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post #14 of 34 Old 07-16-2019, 09:22 PM
mikeundi
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Wasn't there a mod like this for the ZJ waay back in the day? I remember ~99-2001 when I was in college someone on JeepsUnlimited had a box they were selling that was essentially a pot connected to the IAT.
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post #15 of 34 Old 07-16-2019, 10:42 PM Thread Starter
BilletHorse
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Today was a setback, possibly a big one. The POT shorted the system and now the sensor is reading too hot. I bought a new sensor and it has the same readings, even after removal of the POT and resistor.
I'm afraid I may have dinged the ECU.

Should have mounted the POT in a cooler place.

Paying the price for experimentation, irritating because my mods should not have been an issue.

Not totally sure where to go from here, I am reading 5v on the supply side at the connector.

It could also be my OBD2 reader and Torque program, but I don't think so because everything else seems to be reading properly.

I should have just left it with the 4.7k ohm resistor in there and not tried the POT because that was working well.
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