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Old 07-30-2002, 10:59 PM   #1
paulw
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Default Link and IAT

I removed my MAF and was reminded that the inlet air temperature sensor is in the MAF housing. I know the Link manual mentions IAT compensation and how to adjust it but what values do you use? Is this done automatically by the Link?

Inlet Air Temperature (IAT) Allows adjustment for compensation
of inlet air temperature on air/fuel ratio. Cold air is denser,
so for the same throttle position, the volumetric efficiency of
the engine will reduce as air temperature increases. As inlet
air temperature rises the fuel is reduced to compensate for
the lower air density. The number in brackets shows the
actual air temperature in degrees Celsius. The fuel correction
number is displayed on the right.
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Old 07-31-2002, 12:52 PM   #2
Quantum-Racing.com
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It has a 'map', yes. It's before the turbo, so they're kinda guessing what sort of system you have, though.
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Old 07-31-2002, 01:11 PM   #3
nmyeti
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Quote:
Originally posted by Quantum-Racing.com
It has a 'map', yes. It's before the turbo, so they're kinda guessing what sort of system you have, though.
Humm... the map sensor on my car is NOT before the turbo. You must have one of those weird WRXs.
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Old 07-31-2002, 01:38 PM   #4
Austin
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FWIW, the stock ecu sets a default Intake air temp value of -40C when the MAF sensor is unplugged/removed.

I don't know what sort of bad sensor default values the link sets...
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Old 07-31-2002, 01:39 PM   #5
davidm_sh
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Good topic becuase I actually wanted to know how this "feature" works as well. I think the adjustment for it is called "ambient air" or somthing like that in the fueling control area. BUT I have NO idea what generally happens when you increase or decrease that value. I don't know about decrease since it seems to start at 0 but [shrug].

So far I have driven my car hard at high boost with IAT ranging from 25C - 40C and everything seems to be ok as far as my A/F goes so ... [shrug] again .

Anybody have any usefull information on this setting?
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Old 07-31-2002, 01:43 PM   #6
paulw
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I just spoke with Link USA. The IAT is a "read-only" function and is not used to adjust anything. As explained to me, since the MAP readings are already temperature dependent, the link does adjust for changes in inlet temperature
using the MAP sensor.
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Old 07-31-2002, 01:43 PM   #7
ScoobieSnaX
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I'd really like to know as well
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Old 07-31-2002, 02:24 PM   #8
Jon [in CT]
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Quote:
Originally posted by paulw
I just spoke with Link USA. The IAT is a "read-only" function and is not used to adjust anything. As explained to me, since the MAP readings are already temperature dependent, the link does adjust for changes in inlet temperature
using the MAP sensor.
Weird.

It seems to me that, at any particular MAP, the air inducted into a cylinder would contain a lot more oxygen when it's at low temperatures compared to high temperatures. I would think that any ECU trying to contol a turbocharged engine based on MAP would also need to know the manifold air temp to correctly calculate injector pulse width.
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Old 07-31-2002, 03:35 PM   #9
davidm_sh
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Well I just got off the phone with Link USA as well and talked about this and MANY other topics relating to the Link and they basically told me that the temperature differences between pre-turbo/intercooler and post turbo/intercooler are fairly insignificant when it finally gets to the intake manifold (in terms of ambient air changes); i.e: you really won't run that much richer or leaner based off your fuel map given ambient temperature changes ranging from 110F to say 30F.

Since I have only had the Link for a couple of days we will see if this hold true when winter time comes . I have a feeling some "tweaking" will be necessary though... only time will tell.

On a related note the "ambient air" control is meant to adjust this but Link USA said this is more an adjustment for EXTREME hot like in the african deset type of stuff... and even at that it will make quite little difference.
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Old 07-31-2002, 03:45 PM   #10
Jon [in CT]
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Quote:
Originally posted by davidm_sh
Well I just got off the phone with Link USA as well and talked about this and MANY other topics relating to the Link and they basically told me that the temperature differences between pre-turbo/intercooler and post turbo/intercooler are fairly insignificant when it finally gets to the intake manifold (in terms of ambient air changes); i.e: you really won't run that much richer or leaner based off your fuel map given ambient temperature changes ranging from 110F to say 30F.
Wow. You Link guys are lucky. It appears you can get rid of that stupid intercooler as it doesn't make any difference.
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Old 07-31-2002, 03:49 PM   #11
davidm_sh
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Quote:
Originally posted by Jon [in CT]
Wow. You Link guys are lucky. It appears you can get rid of that stupid intercooler as it doesn't make any difference.
. HEY I didn't say I completely bought that story... like I said I will see what happens when it gets much colder out. Maybe he has a point maybe he doesn't. All "I" Know is that the stock ECU "compensates" for variances in ambient air temperature. Now this maybe true but I don't think ANYONE knows just HOW MUCH it actually compensates. The Link USA person said there are sophisticated standalones that allow you to map a curve to compensate for fueling (leaner when warm richer when cold) but he says by and large it's a very small correction factor. So... we shall see.

And yeah getting rid of intercooler = weight reduction baby . Especially my porky air to water intercooler [heh]... that has to be at least 0.1-0.2 in the 1/4 right there!!
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Old 08-01-2002, 12:32 PM   #12
paulw
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Tariq at Link USA sent me this correction:



The system used by the PossumLink is designed to maintain the same air-fuel ratio with variations in inlet/air temperature. This correction factor works between the temperatures of 0 and 50 degrees Celsius. The actual value used by the ECU is temperature dependent. A typical value is 10(Larger number more fuel). It works in the following way. At zeros degrees Celsius the correction factor used by the ECU is 10. At 50 degrees Celsius the ECU will use 0 as the correction factor. The number displayed on the Tuning module or PCLink Software is the “raw” value before it is scaled by the ECU. Between 0 and 50 degrees the value is interpolated based on inlet/air temperature. i.e. at 25 degrees the correction factor is 5.

I wrote back to him that I always see a zero as the correction factor regardless of the IAT. Anyone ever see a "correction factor" number that varies with temperature?
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