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Unread 01-09-2011, 08:08 PM   #1
crimedog
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Air Intake Temp Sensor unattached - AFR issues?

I installed an intake this weekend. There was no bung for the ATS. I left it the pigtail taped out of the way and covered up. The sensor is in bubble wrap in the glove box.
Questions:
1. What is the default AFR for null return on ats voltage? Will the CPU dump fuel into it to avoid lean?

2. If I weld my own, should it go between the the filter and the egr return, or can it go upstream of the filter?

Oh, '06 TJ 4.0 auto.

Please do not respond if you are going to do the following:
1. Preach about CAIs, MCAIs, Filtration, or any of that.
2. Ask me the name of the CAI, as I am calling them tomorrow to find out if there was a mistake. PM me when this is over if you want opinions.
3. Tell me to "search the forum". I looked. If you can find it, I will gladly eat crow.

Yours in Jeeping,
Crimedog

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Unread 01-09-2011, 08:50 PM   #2
oakmckinley
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Whoa.
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Unread 01-10-2011, 08:20 AM   #3
crimedog
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Huh? Why "Whoa"?

Every other vehicle I've owned has had a forum associated with it that was chock full of engineers, techs, and fabricators, as well as people that dilute the signal-to-noise ratio, but that can never be helped.

Is there a different way to find these people (the first three) and to ask them? Someone help me with the secret bat-signal....

--crimedog
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Unread 01-10-2011, 08:24 AM   #4
Unlimited04
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You need to keep the air temp sensor in place. yes, it will screw stuff up. For 05-06 models, the intake tube must have a way to attach the sensor. For 97-04 models the sensor is in the intake manifold. There is no EGR return.
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Unread 01-10-2011, 08:53 AM   #5
crimedog
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No egr.

Sorry, brain fart. The pcv has a return to the intake.

The voltage, though, is what? What does the CPU default to? Is there a 'safety mode' that runs on the rich end of the table? I guess I am really asking if there is anyone out there with a factory repair manual.

I appreciate the reply.
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Unread 01-10-2011, 11:49 AM   #6
Unlimited04
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Quote:
Originally Posted by crimedog View Post
Sorry, brain fart. The pcv has a return to the intake.

The voltage, though, is what? What does the CPU default to? Is there a 'safety mode' that runs on the rich end of the table? I guess I am really asking if there is anyone out there with a factory repair manual.

I appreciate the reply.
the FSM does not go into that much detail with regard to the air sensor. But you still need it.
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Unread 01-10-2011, 12:28 PM   #7
55willystruck
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I agree with above from various other research that it is needed, however going through the FSM for my '05, I cannot find the detail you are asking. I have been told that it should throw a code if not seen or has been removed, however during an older cowl intake installation I actually broke the guard and ordered a new one. Ran without for a day or two, didn't really "notice" anything per se different, nor did I trigger any codes. I have since removed original cowl intake and moved to a mustang style box instead for various reasons. From other searching I've done and talking to those who build some of these items, it has been noted to provide the "best" temp readings and provide the closest AFR the closer it is to the TB where it counts. My current setup is a few inches above the TB just prior to my 90 where it dumps in at. I will be swapping out my sensor here soon as soon as the new one comes in. It's been so long I have forgotten WHICH sensor I have installed in the current setup and for other running conditions, going to change out a few things with "known" good parts/sensors. The coolant temp sensor being another.

Yes, I'd weld a new bung in to get the IAT sensor back in the tube. For location, best I have found is to be as close to the TB as possible, so mine is just before the 90 as mentioned where it dumps in-thinking it would prevent some slight fouling from anything that might escape the TB back-carbon type from fuel, etc. If you remember the stock sensor was basically in this same place, only a few inches back yet. At least on the '05 models. Prior years had the IAT sensor on the manifold and found it was too "hot" there so the better choice was in the air tube itself where it saw "real" air coming in. There are a few various scan guage digital readouts that can provide actual temps if you get the right sensors for the readout to tell you what temps are at these various sights. Spendy but I guess provide good info depending on what you want.

Sorry, can't help with anything else. I'm assuming you haven't thrown a code either yet at this point, hence the reason for your question?

Best of Luck,

Mike
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Unread 01-10-2011, 01:06 PM   #8
Jonny Jeep
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The resistance of the IAT sensor varies with temperature and the computer obviously uses this data to control fuelling. If there is no IAT sensor connected the computer sees this as an extremely low temp and will use excessive amounts of fuel. Here's the chart of temp versus resistance from the FSM...

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Unread 01-10-2011, 08:58 PM   #9
crimedog
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Perfect - Thanks, and one more Q

@55willystruck: The fouling was no different than in stock form? I can get it in there ASAP. The manufacturers put a grommet in the mail today. I think I can get one from AA or PB pretty easily, as it is only a 3/4" hole that needs drilling.
Also, I threw a code IMMEDIATELY, but there have been no driving issues. It probably helps that it has been around 30F here (or less) when I was driving these last few days.

@Jonny Jeep: That is exactly that for which I was looking. Thank you. I know now that I am running a little rich, which is fine for the 20 miles I have driven it, instead of way lean, which is really bad.

I wonder how much work the down stream O2 sensors are doing in adjusting AFR? Just an idle musing at this point. I'll have that IATS back in in a jiffy.

Again, tons of thanks -
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Unread 01-11-2011, 02:17 AM   #10
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Last time I looked, no, no issues. I'll be pulling it out again in the next couple days and know better as I bought two of them when I did the swap and will be changing out the coolant temp sensor so I may as well swap in my other good one just for a "known" good sensor. At least as "known" as "new" can be... Having run it for some time now though in this position and pulled it frequently in the early testing, never did notice any fouling then. I'll check again then get back to you. Mine uses a silly two sided V style wedge thing for the factory setup. I THINK the main hole size was either or very close to 3/4" though, so what you have should work. My tube is a flex style though so I think I went a about a 1/2" size-slightly bigger maybe-and used the flex in the tube for a secure, solid fit-being sized slightly smaller than the actual sensor OD was anyway-if that makes sense. I'll check it out and let you know.

Best of Luck,

Mike
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Unread 01-11-2011, 03:53 AM   #11
ratmonkey
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jeep uses a speed density system. Intake charge temps are critical to your afr. The o2 sensor data can only do so much after the fact as you are leaving out data critical to the initial fuel and spark map being used.
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Unread 01-11-2011, 04:10 AM   #12
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don't forget about timing! I know many timing tables are IAT dependant was well.

If you search around, different people will give you different opinions as to where to put the sensor. Some will say as close to the motor as possible. This will give you the truest reading of air temp before the air reaches the cylinders. The sensor will be subjected to heat soak from the intake tube and radiating engine heat. On the other hand some will say put it as close to the air filter as you can. That way the computer sees the temperature of the AIR before heat soak gets to it.

The real debate to these two theories is this. How is the computer setup to read? Does it want to know the air temp at the manifold, or ambient air entering the system (as a whole). Does the computer compensate for heat soak of the sensor? If so, you want it a stock-ish location. If not, you want the snesor as far away/isolated from heat as possible. Since fuel and timing tables are IAT dependant, you can see how this could make a difference.
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Unread 01-11-2011, 07:36 AM   #13
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Quote:
Originally Posted by Texan32 View Post
The real debate to these two theories is this. How is the computer setup to read? Does it want to know the air temp at the manifold, or ambient air entering the system (as a whole). Does the computer compensate for heat soak of the sensor? If so, you want it a stock-ish location. If not, you want the snesor as far away/isolated from heat as possible. Since fuel and timing tables are IAT dependant, you can see how this could make a difference.
The IAT is important as it sends the message to the computer of how hot the intake air is. I suggest you mount it in a similar area as stock, 6" or so from the TB. If you have a pre-'05 model get the newer plug in type as it'd be easier to install. You want to insulate the air tube and the area the IAT plugs in. On pre-'05 models the IAT was mounted in the manifold-read: heat sink. The tube mount is much better as it comes closer to reading the actual intake air instead of being swayed by other factors like gathering heat from the engine bay and manifold. I have the MCAI and insulated the steel intake tube with 2 layers of exhaust wrap. You don't want to fool the computer with a false reading, but to benefit from a true CAI you do want to send a true reading. If you are indeed pulling air from outside the engine bay insulate the pipe. It's hot under that hood!
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Unread 01-11-2011, 07:42 AM   #14
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plug the sensor in and zip tie it out of the way in the engine bay
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Unread 01-11-2011, 09:43 AM   #15
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As a test I unplugged mine and drove around. I have a Scangauge II. The IA reading was just two dashes, but the fuel economy was really poor (very high litres/100km), just like it is on an extremely cold morning. I think this supports Jonny Jeeps reasoning.
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