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"IAT = Intake Air Temp sensor" on the Focus?

35K views 66 replies 16 participants last post by  lourenco 
#1 ·
\"IAT = Intake Air Temp sensor\" on the Focus?

After running across the below quote on the FordChip website, I did some searching here and didn't come up with much. Most search results came up with: "immediately". Forgive my ignorance, I'm still somewhat of a noob when it comes to all the details. It seems that the more I research, the more I find out how little I know.

Blown cars and IAT/ACTs

IAT = Intake Air Temp sensor.
ACT = Air Charge Temp sensor.

These are two different names for the same sensor. The EEC uses these sensors to help determine ambient air temps. These sensors are always mounted after the MAF and before the cylinder heads. On most newer Fords they are mounted in the inlet tubing before the throttle body. Beginning in the late 90s Ford started using an integrated MAF/IAT design. This design now has a 6-wire MAF vs. the old 4-wire style.

FordChip highly recommends that any blown car remount the IAT/ACT to a position between the blower/turbo and the throttle body. By doing this the EEC will be able to see the temp of the "boosted" air and can be calibrated to remove spark only as necessary under boost. This is a great benefit and safety measure for blown cars. In hot weather the EEC will be able to "see" the air temps and can pull the necessary timing. On those cool days the EEC will allow you to run as much timing as possible safely. This prevents a car that was calibrated on a cool day from "knocking" when the weather gets warm. It also allows max power on those cool days.

FordChip is one of very few tuners that can max tune a blown car using the IAT/ACT. The "other" off-the shelf companies can't. We have datalogged 100s of cars can get you close even by mail-order if we know your engine combo, blower and max boost.
Anyway, have we [FJ] looked onto relocating the IAT sensor on the Focus? Is it even really a big deal? What specific effects does the IAT have on the Focus ECU?

The Focus has a 6 wire MAF right? So that would mean that the IAT is integrated into the MAF sensor right? What would it take to relocate the sensor? I'm thinking that you would have to get an IAT sensor from another (older) car and mount it somewhere after the turbo. Then re-route the appropriate wires from the MAF to the new IAT sensor. I guess finding an IAT sensor that provides the same signal as the integrated MAF/IAT could be a problem.

Any thoughts?
 
#2 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

Good find!
The thought has crossed my mind before, but I'm nowhere near putting money down for FI yet, so I haven't really looked into it. It would make sense that it would benefit the Focus to sense the actual air temperature before it goes into the engine. That is, the air after it's been compressed AND after it's had any cooling (if applicable) performed. Hopefully it's just a matter of disconnecting whichever wires are for the IAT sensor from the MAF and re-connecting them (and any "power" type wires that might need to be duplicated) to a seperate sensor. A quick look at the wiring diagrams would probably help unravel a good part of this mystery.

An interesting thought I just had... Would it be beneficial to split the IAT sensor even in the case of a JRSC? Obviously it heats the air up a bit under boost... It'd seem like it'd be safer for the engine to know the actual temperature. Where would you put it? Just drill and tap a hole in the manifold? Also, what effect would a water injection system (on the Jackson kit or otherwise) have on the IAT? Would it be able to pick up the water's cooling effect in the manifold or does the cooling not occour until the water actually gets into they cylinder head?

I'm most interested in the IAT re-location aspect at this point, so don't anybody get too sidetracked by my JRSC/Water Cooling twist just yet.
 
#3 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

Damn Penuin, always thinking. Personally I have a Zx2, but the earlier version that does have a seperate IAT sensor. Supposedly, this is reads the temp of the air and gives the info to the PCM. From that, the PCM adjusts the a/f mix and even a little timing from what I gather. I had this idea a while back on teamzx2 about mounting the IAT after a turbo to get a really hot reading (which would retard timing on it's own and help with a tuning solution). After a couple days Tom shot it down becuase he figured that the timing table wasn't large enough to accomodate for the big of a temp difference.

http://forum.teamzx2.com/viewtopic.php?t=7467&highlight=timing

I still wonder though....
 
#4 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

I think (hope) Tom was only trying to say that you couldn't use the IAT table to SOLEY correct for a re-calibrated MAF and larger injectors. I wouldn't expect it to be able to correct for that. It SHOULD be able to help with varying intake air temperature (hence it's name
). Here's a quick clipping from the wiring diagrams. I'm not up on my electronics symbols (and am hungry and should go make something for dinner
) so I haven't fully deciphered this yet... But it doesn't look to be THAT tough. Enjoy!

 
#5 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

Thanks for that link to that thread. I think Tom is probably right.

So from what he's saying, you would not want to count on the IAT to remove timing. And that makes sense. I was just curious if it was of any benefit. It only makes sense that you would want the PCM to know what the real temp is. Temp at the MAF is completely irrelevant. So I guess the question for me is can the SCT software adjust for the IAT feedback being out of normal range? In other words, can the tables be modified to understand and react. And is it worth the effort? I guess I'll have to ask the SCT guys that one.

And Charles, I'm going back to my thermodynamics classes here so bear with me. When the water mist is introduced into the hot air, it essentially changes states from liquid to gas. It takes heat energy from the hot air to change the water from liquid to gas (latent heat of evaporation?). Kind of like how a pot of water boils on a stove. The temperature of the water cannot get any hotter than the boiling point (100C). But the burner is still introducing heat energy into the water to convert it to steam or gas. OK, that may not be the best analogy but that's all I've got right now. The question is, how long does it take for the water to be converted to gas? Things are happening pretty fast. Regardless, I think an IAT sensor mounted as far away from the Water Nozzle would be optimum. And certainly more accurate than the reading at the MAF location. But can we use that value? I don't know? One way or the other, once it gets into the combustion chamber and the intake valves close, it gets compressed and therefore heated up yet again. But its starting with a cooler charge.
 
#6 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

Just a couple more to throw into the mix.
Then off to see about dinner. Really, I mean it this time.




<font class="small">Code:</font><hr /><pre> TEMPERATURE SENSOR VOLTAGE AND RESISTANCE SPECIFICATIONS
.---------------------------------------+-------------------------------------------.
| Temperature | Temperature Sensor Values |
+------------------+-------------------+------------------------+------------------+
| øC | øF | Voltage | Resistance |
| | | (volts) | (K ohms) |
+------------------+------------------+------------------+------------------+
| 120 | 248 | 0.27 | 1.18 |
| 110 | 230 | 0.35 | 1.55 |
| 100 | 212 | 0.46 | 2.07 |
| 90 | 194 | 0.60 | 2.80 |
| 80 | 176 | 0.78 | 3.84 |
| 70 | 158 | 1.02 | 5.37 |
| 60 | 140 | 1.33 | 7.70 |
| 50 | 122 | 1.70 | 10.97 |
| 40 | 104 | 2.13 | 16.15 |
| 30 | 86 | 2.60 | 24.27 |
| 20 | 68 | 3.07 | 37.30 |
| 10 | 50 | 3.51 | 58.75 |
+------------------+------------------+------------------+------------------+</pre><hr />

I think those values apply to all temperature sensors (IAT, Coolant, Oil, etc.) but I'm not 100% sure yet.

I'll clean up the table a bit more later... At least it's readable.

[noob question] What kind of a range of intake air temperatures are we talking about here with a typical FI install? [/noob question]
 
#7 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

Thanks for the schematic Charles


I can only decipher a few things (And I wouldn't call it deciphering. More like point out the obvious):

(1) Ford, at least for the Focus, refers to it as an ACT - Air Charge Temperature sensor.

(2) The labels on the wires like '.75 GN/RD' stand for wire size and color. For example: .75mm^2 Green wire with Red Stripe. FYI - The mm^2 is the metric equivalent of AWG.

(2a) I think the other 'marking' on the wires should relate back to the computer. Is there another diagram with those same markings?

(3) wwww = resistor

(4) wwww with arrow = variable resistor

(5) The other symbol there in the circle is some type of transistor.

I know this is all pretty much elementary for some of you. But I had to refresh my memory 'cause that transistor symbol was bugging me.
 
#8 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

im sure it could work.. but would need to be relatively well placed... caus i mean.. its not like there isn't a IAT already in there.. yes the air temp must drop a little from the space separating the iat from the turbo.. but you'd have to know exacly where to put it.. if its right after turbo.. then the air mihgt be too hot? retard too much timing maybe?.. or after the IC .. i mean the reason that the iat is close to the throttle is that the air will not have too much temp change after the iat sensor before entering throttle etc..etc...
 
#9 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

Penguini and Charles, good work!

Yes, you're basically right on. The *proper* way to tune a car is to factor in the post compressor air temperature, and retard timing/add fuel accordingly. That is the best way to squeeze everything out of the motor that you can.

Some tuners just ignore this effect completely. That's what Greg Banish did to me when I went to his shop. It was so bad, it didn't even run properly at cruise.

In my case, I have had to mount the IAT sensor before the turbo. I want to mount it after, but it was causing problems. The Pectel comes with a slow air temp sensor. It has a lot of mass in the sensing element, and a large heat conduction path. Originally I had the thing mounted right in the throttle body elbow, but what happened was that while idling, the airflow was so slow, that heat was conducting from the head, through the manifold the TB, then heating the sensor. So, as I sat waiting in line somewhere, the sensor started to heat up, and it leaned the engine out. Badly.



I've HAD to move it right near the filter, so that there is a long conduction path to the sensor mount. Even now, heat still creeps from the turbo through the intake pipe to the sensor. It still heats up, but not as much or as fast.

Eventually, I'll get a fast response sensor from Pectel, which has a small filament more like the Ford sensor. This will more accurately measure the temp of the air, not the mount.

I have managed to tune it so that it runs, even though it's not taking into account the heat of the compressed air. Basically, it's factored into the base load maps. Luckily, compressors are fairly consistent, and they will always heat the air the same amount for a given boost and inlet temp. So, if your base maps are tuned right, you'll richen it up enough to account for the fact that under boost the temps are not measured.

Once I get an intercooler however, it gets much more difficult. Intercoolers are not that consistent. The amount that they cool can depend on heat soak, air speed, etc... so for a given inlet temp and boost pressure, you could have different intercooler outlet temps.

To tune around this in the base maps, you are going to have to leave a lot of power "on the table". You end up tuning conservatively for low airflow/heatsoak conditions, and then when the intercooler is working well, you won't get all the timing that you could.

This is one of the reasons I don't have an intercooler yet. I need to get a Pectel "fast response" sensor, and mount it after the intercooler. This sensor has a much more sensative filament.



It won't suffer from heat soak as much. I'll get a more accurate measure of air temp, and my base maps can be tuned more aggressively.

All of this leads to my conclusion:

It's not too hard to get an engine running, just about anybody can do it. However, to get it running SAFELY takes more experience. Some tuners never get to this stage. They tune a motor, it blows up, they blame it on the physical engine or some old wives tales about something or other.

But there's another stage, I think, where a tuner really knows what's what, and allows you to tune an engine safely, WHILE also maximizing the power, SAFELY.

Some tuners who make safe tunes, leave some power on the table, because they aren't doing everything they could. Maximizing the system. That's always been my goal.
 
#10 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

You bring up another good point about the effects of an IAT in an intercooled setup. If you have a good IAT and you are using an air/liquid intercooler, its not as important to monitor the water temp and regulate it with a pump on/off function. You may be able to just leave the pump on all the time and count on the IAT to compensate for differing intake temps. Therefore, making full use of the intercoolers cooling ability. Instead of worrying about tuning the timing and fuel to work within a certain temperature range. And then trying to maintain that temperature range within the intercooler liquid with a temp sensor and relay activated pump. Am I anywhere close?
 
#11 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

While poorly attempting to do some trouble shooting on my g/f's '95 3.8 Mustang, I found something interesting out. It has a 4 wire MAF and a separate IAT sensor. We were at AutoZone and I asked them to look one up. They stock them and it goes for about $13. (Just checked parts.com and its $40 from Ford) Now, I don't know anything about the quality of the AutoZone IAT. And I don't know what the pricing would be for those fancy Pectel ones. But at $13, it might be worth a try. And we may get lucky because if its for a Ford, it might send the same signal or values to the ECU compared to the newer 6 wire MAF/IAT integrated setup we have.

Also, the sensor is what I would call "poke through." In other words, it goes through about a 3/4" hole in the intake tube. There's a flange protruding from the intake tube that the sensor plugs into and then is hose clamped. If it turns out that this is an appropriate sensor, I think I may just have the perfect place to locate it. On the Aerocharger intake plenum, there's a large hole for the SFMS. When the SFMS comes off in the next month or so, I could easily have a plate fabricated to cover the hole with a smaller hole and an appropriate flange for the IAT sensor. Edit: Forgot one thing. It would probably make sense to have the plate fabricated from phenolic plastic to attempt to isolate the sensor from the heat soaked Aerocharger plenum. Or at least a phenolic sleeve for the flange to hold the sensor.

So, does anybody know how to figure out what type of signal the ECU is looking for and if the '95 3.8 Mustang IAT sensor might be appropriate?
 
#12 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

Just pulled this from the DTC codes list in 'Team Tech':
P0112 - Intake Air Temperature (IAT) Circuit Low Input Indicates the sensor signal is less than Self-Test minimum. The IAT sensor minimum is 0.2 volts or 121°C (250°F).

P0113 - Intake Air Temperature (IAT) Circuit High Input Indicates the sensor signal is greater than Self-Test maximum. The IAT sensor maximum is 4.6 volts or -50°C (-58°F).
So there's our range: -58°F to 250°F Is that an actually working range for the sensor? I highly doubt it. I'd imagine the computer might get pretty confused if it saw an IAT reading of 250°F. I wonder how high it goes in the stock tables? And I wonder if I can correct or compensate for it with the SCT software? (Yet another question for the SCT guys and yet another reason why its probably not a good reason to put an IAT sensor on a car with a stock computer program) Edit: Just re-read Charles's post earlier with the table. Can you clarify where those values came from? Is this an indication of the range that the computer is programmed for? I also noticed that it looks like he gave us the two wires to 'play' with when trying to hook up a remote IAT.

The above dtc info is for a Focus. I wonder if it is the same for the Mustang? If so, that would lead me to believe that the sensors are at least similar.

And this may seem like a really dumb question from a guy with a turbo on his car, but what's think the maximum intake temperature after the turbo?
 
#13 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

The pectel air intake sensor must be really slow to respond since I can wot in 1st gear up to 4th gear, and It still reads about the same 100F. I would think the tempature should go up some.
 
#14 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

The values in the table I posted came off of the Ford Factory Service CD (June 2000 I think). I don't think the section differentiated between IAT sensors... One set of values for all sensors... I THINK. I bet I've got wiring diagrams and everything for the rest of the cars Ford made in 2000 too. I wonder if the Mustang used a seperate IAT or if it was integrated into the MAF... Hmmm.

I'll dig around some more tomorrow (er, later today) if I get some time.
 
#16 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

Penguini, nice idea, but I did that and it didn't work. I put the sensor in the AC plenum, using a Delrin plate, and it heat soaked.
I assume this is the sensor that was giving you the heat soak problem?


That sensor looks like it has alot of metal in it. And I would expect it to heat soak. Even if insulated by plastic. But from what I could tell, the Ford style sensor is all plastic. Except for the contacts and the sensor itself. It still might be worth a shot. Maybe I'll stop by the auto parts store tonight and pick up one of the $13 sensors for reference. Edit: Removed the moronic part about testing the sensor in the oven (hopefully before anybody read it). I'll have to get out my instrumentation book and try and figure out how those sensors work. I'm pretty sure my original idea will not work.
 
#18 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

What do you guys think of this:


Its from a 96-01 Mustang and its all plastic. Its going to be a little tricky designing an adapter plate to hold it but I think its doable. (I was wrong before when I thought that the 95 Mustang sensor was all plastic.)

Do you think I should still plan to fab the adapter plate out of plastic? Or does the fact that the sensor is plastic negate any heat sink possibilities?
 
#20 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

Yeah, that's it. I had a ZX2 and on the Iceman I had, there was a pre-made opening that took the sensor's male end about 1/2 a foot to a foot from the throttle body. Oh, and that was a BJT transistor, eg: current controlled.
 
#21 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

What do you guys think of this:


Its from a 96-01 Mustang and its all plastic. Its going to be a little tricky designing an adapter plate to hold it but I think its doable. (I was wrong before when I thought that the 95 Mustang sensor was all plastic.)

Do you think I should still plan to fab the adapter plate out of plastic? Or does the fact that the sensor is plastic negate any heat sink possibilities?
This is the IAT that I use. It is the same one that the Lightning Truck uses. Thats the MAF that I use so I had to use the seperate IAT. I just drilled a hole in my intake and put a rubber grommet in it then pushed the IAT into the grommet. It's been working that way for about a year. It wires to the original (outside) wires from the MAF connector.
 
#22 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

^^^^^^ Thanks for the info.
So, it looks like this type of sensor will work with the Focus ECU. Since the sensor will be under pressure, I might do something slightly more fancy than just a grommet. Looks like this is a go. Thanks for all the help. I'l let you guys know how it works out once I get rid of my SFMS and re-locate the IAT sensor. Although I'll be changing so many things at one time (MAF, Injectors, re-locate IAT, 4 bank SCT chip) it will be hard to notice the impact of just one component.
 
#24 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

But why change it it does very little if anything ,I have played with this on my car and didnt like the way it ran and there was NO power gain

If you have enough controle over the ECU to tune for boost you can also tune for hot/cool air charge


Tom
 
#25 ·
Re: \"IAT = Intake Air Temp sensor\" on the Focus?

Why is it bad for the ECU to know the actual air temperature before it goes into the engine?
The better the info that you feed the ECU the better it can do managing the engine. Why not take advantage of its capabilities? I would think that not utilizing the IAT in the right way would be a "band aid" solution to proper tuning, and we all know what you think about those.
 
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