IAT insanely high?
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Joined: Apr 2006
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From: Huntsville
IAT insanely high? Trying to figure out my random misfire. I ran my vcmscan and found that my IAT runs 106-110 is this normal or overly hot? The car had been parked for 3 hours prior to me running the scan any help is appreciated thanks in advance!!!
yes, let's put IAT sensors as far as possible from the intake, cause if they measured the actual temperature of the aircharge, all the other hacks we've put into the 'tune' would come out. not smart.
Originally Posted by RedHardSupra
yes, let's put IAT sensors as far as possible from the intake, cause if they measured the actual temperature of the aircharge, all the other hacks we've put into the 'tune' would come out. not smart.
Originally Posted by RedHardSupra
yes, let's put IAT sensors as far as possible from the intake, cause if they measured the actual temperature of the aircharge, all the other hacks we've put into the 'tune' would come out. not smart.
Any change in charge temp should be resolved in B4901 (Charge Temp Blending). Just because my lid radiates 110*F temps doesn't mean the air is that hot going into the motor. I put the IAT just in front of the lid to get the underhood temp of the air entering the box, which (at speed) is usually a few degrees above ambient.
Although I've been trying several different methods of tuning to learn for myself the pro's and con's of each, it doesn't mean I've dismissed everything I've learned over the past 2+ years. As a matter of fact, now that I have relocated the IAT, I've gone back to a SD tune to see the effects. Next is probably COS5, which if it works as well as everyone says it does, its probably where I'll stay with my tune. My goal in all of this was to see if there was a quicker/easier way of getting the car to run and run right. What I found was, you can get it to run and run close to right without spending days on SD tuning. But, the results will have a few quirks to live with.
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I don't know, and bet most of us don't, how the IAT
value is manipulated to produce the air charge number
for speed density. It's questionable whether you want
the real outside air reading, the manifold air temp or
something else. Which inlet? Expanded or unexpanded,
compressed or uncompressed air?
Then rub the IAT up against ECT in that whole charge
bias temp mess....
Relocating the IAT sensor to be in the high velocity
air stream is better than leaving it in a backwater
corner of the lid where it won't be driven into line
with the real air temp (whichever one it may be).
I believe this is part of why it's integral to the 85mm
MAFs (the rest probably being economic).
Figure at any reasonable airflow the real air temp is
going to be less than the heat-soaked wall temp.
By varying, take-a-wild-guess amount.
I don't think a location that senses true outside temp
is any less realistic than in-the-pipe given that you
tune it in. Depends on what you believe for tract
heating effects and what the PCM does to the data
(does it model throttle-as-expansion-valve cooling
with the MAP & BARO data, or is it assuming the
IAT is in fact the "raw air" temp?).
If it were a straight up real speed density setup,
like MAP*RPM*(273/(IAT+273))*VE() then you'd
want the IAT to be in-manifold so it's on the same
air-sample basis as the MAP (n=PV/rT, P and T need
to be consistent or somehow massaged to be).
value is manipulated to produce the air charge number
for speed density. It's questionable whether you want
the real outside air reading, the manifold air temp or
something else. Which inlet? Expanded or unexpanded,
compressed or uncompressed air?
Then rub the IAT up against ECT in that whole charge
bias temp mess....
Relocating the IAT sensor to be in the high velocity
air stream is better than leaving it in a backwater
corner of the lid where it won't be driven into line
with the real air temp (whichever one it may be).
I believe this is part of why it's integral to the 85mm
MAFs (the rest probably being economic).
Figure at any reasonable airflow the real air temp is
going to be less than the heat-soaked wall temp.
By varying, take-a-wild-guess amount.
I don't think a location that senses true outside temp
is any less realistic than in-the-pipe given that you
tune it in. Depends on what you believe for tract
heating effects and what the PCM does to the data
(does it model throttle-as-expansion-valve cooling
with the MAP & BARO data, or is it assuming the
IAT is in fact the "raw air" temp?).
If it were a straight up real speed density setup,
like MAP*RPM*(273/(IAT+273))*VE() then you'd
want the IAT to be in-manifold so it's on the same
air-sample basis as the MAP (n=PV/rT, P and T need
to be consistent or somehow massaged to be).
Last edited by jimmyblue; Jul 6, 2007 at 01:12 PM.
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Verdad Gallardo That is a valid point. Why wouldn't the IAT sensor be built into the manifold itself? It seems that it would yield the most accurate reading. Or do the calculations within the PCM compensate for its offset?
The answer would obviously lie in knowing the exact calculations used, which may never be known by the end user.
The answer would obviously lie in knowing the exact calculations used, which may never be known by the end user.
jimmyblue, as per usual, you're dead on.
the formula for temperature used in SD equations is IAT+(ECT-IAT)*BIAS, and BIAS seems to be a function of exp(-k*airflow) with some arbitrary k (that's pretty much what describes the heat transfer properties of the hardware)
I've been comparing airmass calculated from SD (MAP, RPM, IAT, ECT, bias, VE,displacement), and MAF and RPM (since it supposed to account for temps automatically), to arrive at a bias curve that produces least errors. so far the method works fine, but it's difficult to find a proper MAF curve without injectors settings absolutely perfect. since MAF calibration is a 3rd order poly of MAFfrequency, i've created a MAF estimator and use that for airflow figures, which cleans up the data nicely. so with a nice MAF and the rest being sensor data, i can arrive at k that yields least error.
do you think this idea is valid? i got a lot more on this if you want, i just gotta run errands soon.
the formula for temperature used in SD equations is IAT+(ECT-IAT)*BIAS, and BIAS seems to be a function of exp(-k*airflow) with some arbitrary k (that's pretty much what describes the heat transfer properties of the hardware)
I've been comparing airmass calculated from SD (MAP, RPM, IAT, ECT, bias, VE,displacement), and MAF and RPM (since it supposed to account for temps automatically), to arrive at a bias curve that produces least errors. so far the method works fine, but it's difficult to find a proper MAF curve without injectors settings absolutely perfect. since MAF calibration is a 3rd order poly of MAFfrequency, i've created a MAF estimator and use that for airflow figures, which cleans up the data nicely. so with a nice MAF and the rest being sensor data, i can arrive at k that yields least error.
do you think this idea is valid? i got a lot more on this if you want, i just gotta run errands soon.