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Thread: IAT sensor location

  1. #1
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    IAT sensor location

    I didn't want to dig up an ancient thread, so I thought I'd get opinions separately. My IAT sensor is currently in the stock location in an aftermarket lid, near the neck. I also have a 100mm aluminum MAF housing using a LS3 card MAF, but the IAT connector is just zip-tied out of the way. I ordered one of the recommended separate thermistors which is faster reacting (if only I could find where I put it ) and also have an IAT extension harness.

    I've read some various threads about the speed of the airflow being high enough between the filter and the combustion chamber that it wouldn't matter if I had the sensor near the hood latch, or near the windshield wipers. Others say to put it in the intake, but since I have an LS3 intake I no longer have the EGR opening of the original LS1 intake and I'm not going to butcher my intake.

    What I want is to have the most accurate temperature reporting for the air mass entering the chamber while minimizing idle heat soak and false lean AFRs without changing PCMs. Has anyone tried using thermal insulation between the top of the radiator and the base of the air filter housing, or around the intake tract?

    Recommendations?
    Last edited by JimMueller; 09-14-2014 at 10:28 AM.
    1998 NBM Camaro Z28
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  2. #2
    Tuning Addict 5FDP's Avatar
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    Why not just put it in the intake tube itself, you want it to measure the air temp going into the intake manifold.

    It really doesnt matter if you put it directly behind the air filter or 3in before going into the throttle body.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
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    For mechanical and airflow reasons the thermistor body is kept
    close to the wall. This makes it more influenced by conduction
    through the leads, from the tube walls. Which heat soak in the
    lanes or parking lot, lean you out, pull timing and then you have
    hard starting.

    It's not about air temp fidelity at high flow steady state.
    If the IAT body takes 10 seconds to cool when you nail it,
    what the hell good is it at the track?

    I say to put it at the coldest air position you can.

  4. #4
    Senior Tuner LSxpwrdZ's Avatar
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    Front bumper and be done, dial in the bias table from there and you'll never get lean stoplight idle. In the manifold works but it's still not as effective as bumper mounting the IAT away from the radiator!
    James Short - [email protected]
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  5. #5
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    Oh, did they fix the IAT/ECT bias tables in the 1998-2000 PCM's? Last I heard the table existed but changes had no effect. Unclear to me if this was due to broken GM or HPTuners code.

    http://www.hptuners.com/forum/showth...ight=1998+bias

    Greg Banish disagrees with relocating the IAT sensor:
    https://forum.efilive.com/showthread...-IAT-heat-soak
    Last edited by JimMueller; 09-20-2014 at 07:01 AM.
    1998 NBM Camaro Z28
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  6. #6
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    You're going to have to accept some error under some
    conditions. Because heat soak error exists, and varies,
    and the PCM doesn't know how much, when or why. It
    can't correct a primary sensor that's lying to it.

    If your IAT is colder than reality, you a high air mass
    calculated, more fuel, less timing (by the main table).
    This is a pretty benign sort of error.

    If your IAT is reading hot, you get false low air mass
    and lean, more main table advance (and no help for the
    A4 line pressure either). You depend on the IAT adders
    to comp the air mass induced excess advance. Maybe
    it suffices, maybe not - stock experience tells me, not.

    With a good cold air setup, at the big end outside air
    and duct air temps are the same (nil time-over-target
    to do any air heating of consequence). At the little end,
    let closed loop deal with the fueling error from a high
    air mass error, and who cares if spark is a little short
    at cruise?

    Mr. Banish may have a theoretical reason for liking what
    he likes, but I've proven out relocation to my own satisfaction
    and no theory is making me go back.

    Now I sure would like to know what the PCM "thinks" is the
    real IAT position of interest. Just for understanding. But as
    far as parking lot practicalities, as close to possible to real
    outside air has worked better for me than any other thing
    I have tried (and I have tried stock airbox, 85mm MAF internal
    and cowl vent, with only the last not-heat-soaking, parked).
    Anyone not running full time fans can extend "parked" to
    "parked, or rolling slower than 30MPH (or so)", because the
    underhood air gets mighty warm if you don't move it.

  7. #7
    Advanced Tuner Cyrperformance's Avatar
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    I agree with the above, as for the simple statements, I had the 85mm truck MAF and would get heat soak rapidly whenever sat, and it was difficult to get the temp back down. I would frequently see 130-140 when the outside temps were 90-95. I just went through installing a seperate IAT and went through about a days worth of temperature readings to find the best location. What I found for my application was to mount it just above the outlet in the intercooler tank.

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  8. #8
    Senior Tuner LSxpwrdZ's Avatar
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    I completely overlooked you having a 98... simple upgrade to a newer PCM with 01-up OS lol.
    James Short - [email protected]
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  9. #9
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    Yeah, that's a lot of unnecessary effort & cost for such limited benefit for a basic build such as mine. I'll just leave it as-is, I don't drag race and so long as my IAT Advance table is reasonable I expect to be fine.
    1998 NBM Camaro Z28
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  10. #10
    Senior Tuner LSxpwrdZ's Avatar
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    Haha true that. Why not just put a MAF back on the car? That'd cure a lot of your issues as well.
    James Short - [email protected]
    Located in Central Kentucky
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    2020 Camaro 2SS | BTR 230 | GPI CNC Heads | MSD Intake | Rotofab | 2" LT's | Flex Fuel | 638rwhp / 540rwtq
    2002 Camaro | LSX 427 | CID LS7's | Twin GT5088's | Haltech Nexus R5 | RPM TH400

  11. #11
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    Quote Originally Posted by JimMueller View Post
    I didn't want to dig up an ancient thread, so I thought I'd get opinions separately. My IAT sensor is currently in the stock location in an aftermarket lid, near the neck. I also have a 100mm aluminum MAF housing using a LS3 card MAF, but the IAT connector is just zip-tied out of the way. I ordered one of the recommended separate thermistors which is faster reacting (if only I could find where I put it ) and also have an IAT extension harness.
    Quote Originally Posted by LSxpwrdZ View Post
    Haha true that. Why not just put a MAF back on the car? That'd cure a lot of your issues as well.
    I already have a MAF installed.
    1998 NBM Camaro Z28
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  12. #12
    Senior Tuner mbray01's Avatar
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    I am still fumbling with why anyone would want to relocate the iat anywhere else except in the intake tube, or intake itself. A place where it is going to measure the true temperature of the air entering the engine, which is what the ecu bases its calculations on. In my experience with iat relocation i have found the few degrees that are pulled at slow speeds are not worth loosing an engine over. I started doing the iat relocation thing, and timing stayed in line with outside temps, however at the track here in south louisiana with heat indexes of about 110-120, and underhood temps close to 170-180. I noticed very audible spark knock on hard launches that we didn't see or hear on the dyno. but were showing up at the track. Doing nothing more than putting iat in intake fixed the problem. And ironically we picked up speed and dropped times. Essentially the iat was only pulling 4-6 degrees in the tune while the kr was pulling between 8-12 degrees, and pinging the hell out of the motor. But this is only my experience and take it as you will
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  13. #13
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    Because in some situations the IAT in the tube DOES NOT report
    true air temperature going by. It reports the wall temperature of
    the tube.

    Your heat-soaked IAT pulling timing, would (if IAT adder retard
    exceeds cylinder-air-mass-error main table incremental advance)
    perhaps prevent some spark knock. This comes down to cases
    with your particular tune values and real and indicated air temps.

    On a cold air setup in the seconds after you nail it, an outside
    IAT is going to read closer to true in-taken air than one that's
    jacked by 60 degrees from sitting in the engine bay. Now your
    tune may, or may not respond well to the truth, especially if
    it was set up based around the lie originally.

    Quote Originally Posted by mbray01 View Post
    I am still fumbling with why anyone would want to relocate the iat anywhere else except in the intake tube, or intake itself. A place where it is going to measure the true temperature of the air entering the engine, which is what the ecu bases its calculations on. In my experience with iat relocation i have found the few degrees that are pulled at slow speeds are not worth loosing an engine over. I started doing the iat relocation thing, and timing stayed in line with outside temps, however at the track here in south louisiana with heat indexes of about 110-120, and underhood temps close to 170-180. I noticed very audible spark knock on hard launches that we didn't see or hear on the dyno. but were showing up at the track. Doing nothing more than putting iat in intake fixed the problem. And ironically we picked up speed and dropped times. Essentially the iat was only pulling 4-6 degrees in the tune while the kr was pulling between 8-12 degrees, and pinging the hell out of the motor. But this is only my experience and take it as you will

  14. #14
    Senior Tuner mbray01's Avatar
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    Not trying to incite a war of sorts. I just feel a need to be very cautious when talking of relocating the iat. Here is why?. How many people have brought cars in with true cai and ones that claim to be. For example
    I have two cars in shop now, both 2012 camaro ss
    one has vararam cold air intake system, expensive but is a true cold air intake. I can let that car run in the parking lot all day and iat will never deviate from ambient more than 5-6 degrees.
    Now take car two, has air raid cai, cheap over the counter autozone special idling in parking lot iat reaches temps of 195-205.

    Now why the difference? it is not heat soak, it is the efficiency of the system involved, the air raid pulls air from behind the radiator, so it is pulling hot air. If you move the iat, you are telling the pcm it is getting cold air, when in fact it is getting hot air.

    Now did you build the car and installed the air intake and know it is an efficient one that pulls from fresh air, then by all means move it.

    I just ask this, of all cars you tune on a daily basis how many come in with that $1200 air intake, and how many with that $200 intake.
    I know I can say of all the walk ins I tune maybe 1 in 100 has the good one, and that is because someone took the time to build the propper mods for the car, not just open a magazine or read a forum.

    Now do I buy the whole heat soaked intake tube? maybe, maybe not. on a cam'd 6.2 air flow at idle is close to 20 grams/sec. The velocity of the air is so high I find it hard to believe that the air is absorbing 60 degrees in an 8" long tube. now in a stock platform, I can entertain that.

    My one true point here why are we moving the iat. Is it truly getting heat soaked, or is it a bad cai, that is pulling hot air. That is the first question that needs to be answered.
    I am not trying to incite a war, I know I have had to fix a bunch of customers cars that were tuned with relocated iats, that were cheap cai. The fix is always as simple of putting the iat back, or get a true cai. then usually the tune is dead on!!!!
    Michael Bray
    Rusty Knuckle Garage
    Slidell, Louisiana
    20yr Master Tech.
    Advanced Level Specialist
    Custom Car Fabrication, Customization, High Performance.
    GM World Class Technician
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