Tuning for cold air

[MAGP]

I'm pretty sure its been discussed before in another thread that the IAT sensor in a MAF system is just used to adjust ignition timing and fueling is entirely done via the MAF and trimming via the O2 sensors

From the VT Series Service Manual Number 4 (so its the V8 book) on page 6C2-1-15

The IAT sensor signal voltage is one of the parameters used by the PCM in calculating the fuel injector pulse width.

Also from the manual but paraphrased this time the PCM considers the engine is running under cold conditions if the IAT signal voltage is between 4-5 volts. Likewise the PCM considers the engine is running under hot conditions if the IAT signal voltage is between 1-2 volts. So normal signal voltage would be between 2-4 volts. With a corresponding change in injector pulse width as the voltage moves up or down.

[Holden202T]

i'd say that's your answer!

the question then is, what does it think for cold air and heated up motor!

either way the end result is probably going to be that its running too rich in the colder air!

[vlad01]

Not according to what The1 said how the code works. Maybe he can confirm if he chimes in?

[Holden202T]

it would have to have some impact on the tune, otherwise why would it be there in the first place ?

[vlad01]

it would have to have some impact on the tune, otherwise why would it be there in the first place ?

I recall he said it only has influence on timing as seen in that table shown couple pages back.

[immortality]

V8 and V6 use totally different PCM's and code (if you are referring to the LS motor)?

I have no doubt the AIT sensor has some input but the MAF is the primary. Also depends on what The1 has done with the code.

Having said that, it's clearly not compensating for the much cooler intake charge but then it's probably cooler than the factory ever tested?

[Holden202T]

thats right, if that motor never had a CAI on it then it probably never got tuned for that condition .... it could even be the MAF that's seeing really lower temps and throwing fuelling out a bit....

[MAGP]

V8 and V6 use totally different PCM's and code (if you are referring to the LS motor)?

Different PCMs yes but its not an LS. IATs and MATs have the same function in VN-VT1 V6 and V8 in bog stock systems as far as IO am aware. They don't just deal with ignition timing they tell the engine how cold the air is as well. It is highly possible the enhanced code has changed things so much that it has no effect anymore but we don't know if that is correct or not yet.

[MAGP]

thats right, if that motor never had a CAI on it then it probably never got tuned for that condition .... it could even be the MAF that's seeing really lower temps and throwing fuelling out a bit....

Yes it could be but it would be because the PCM thinks the MAFs signal is indicating more air not colder air.

[The1]

Yep iat sensor on any enhanced code bin or the factory code is only for spark adjustment, hence the sensor being in the airbox, not a really useful place but it will measure change in intake temp which is all it needs to measure to make the required spark changes, it's nicer though on an L67 to put a temp sensor in the Lim as the change in temperature up and down would be vastly different.

maf is the one in control of fueling, it will pickup on the colder air and read it as higher flow because of the cooling effect of denser air on the hot wire, so it will increase injector pulse time hence your higher fuel useage. If the fueling is out then the injector multipliers tables likely need tuning, the increase in maf airflow will also increase cylinder airflow readings.