Runs a little choppy with higher temp?

[DaddySS]

So yesterday as I had stated I had it dialed in nicely - today on a 30 minute drive with outside temperature about 10* to 20* hotter than yesterday, towards the end of the drive it started to run a bit "choppier" at various speeds and throttle positions - neither the engine temp nor the IAT changed dramatically from the beginnig to the end of the drive but it seemed to get sluggish. Is it just that it pulled fuel over time through the LTFTs? I see the parameter to blend IAT and ECT could that have something to do with it? Is there a way to adjust for this?

[DaddySS]

I think the fuel trims were marginally OK and with the warmer temperature it became too lean. Very interesting that it gets leaner, you would think it would run richer but it is what it is! I added some fuel and it seems to be much better - further testing today.

[SSpdDmon]

My theory...

Heat soak is the problem here. IAT's become affected by underhood engine temps and effectively alter fueling. What I think happens is (and I saw this last night with my tune), the PCM obviously uses the IAT in it's fueling calculations. If there's enough heat soak to get the IAT to read 100*F when the air outside of the car is really 50*F, then the PCM is only going to provide enough fuel for the air density levels at 100*F even though once the car gets moving, the cooler air will get to the airbox. Since lower air temps have a higher density level (more oxygen content) and fueling is being provided based on the assumption that IAT's are correct, this appears as a lean condition until the IAT's have a chance to come back down.

[ViolatorTA]

Heat soak becomes even more evident on an F-Body when you do the free ram air mod. I see heak soak IAT temps of 120F + at times after the car sits for an hour or 2 after shutting down the engine.

[mr.prick]

how would you prevent this from happening?
maybe {B0109} or {B4902}?
{B0109} off will use only IAT temp
in open loop wouldn`t you only want to use ECT?
(that is what {B3605} uses with MAP)
i have noticed that if i drive for a while i`m alright but then i get crazy lean or rich in some areas that i know should be perfect for no reason.
mabe filter out anything above xxx*F or xx*C.
i`m thinking anything over the out side temperature of the car.
this has screwed me up a few times.
maybe there is a good all around temp filter or turn off
{B0109} = blend iat with ect will do the trick.
i also have a cut out air box so this totally makes sense now that you mention it.
i have seen that i hit 117*F IAT temp!

[SSpdDmon]

Playing with the charge temp filters can lead to other side effects. It effectively can alter grams/cyl calculations, and therefore timing. The true solution would be to get the IAT in a spot where it can read the temperature of the air entering the lid without any influence from any other outside factors. Even though that lid is plastic, it can get pretty hot.

I've been debating on getting some kind of compressed air canister (or anything that sprays out really cold) so that I can help to combat this in the staging lanes at the track.

[mr.prick]

i just made an aluminum plate to shield the bottom of my air filter
and noticed a reduction in temp when moving but when i restart there
is hi temps for a min.
this totally explains why after a reflash i would get a wacky lean condition
because the IAT temp would skew my log and i would read rich because of hi temps the it would paste all screwed up.
i am now filtering anything over 93*f.

[mr.prick]

for anyone who is watching this i have found that my IAT temp is about 10* higher than the actual air temp.
i have taken the air box apart and it did not feel all that warm inside , but i noticed the lid held the temp fairly long after i took it apart.
seem the plastic is not immune to heat soak.
if you feel where the radiator and the air lid almost touch the lid gets
pretty warm from the close contact.
i`m sure this is why if you log driving around town on a hot day
you will get rich readings when you wouldn`t other wise.

[DaddySS]

Another thought - we do the rafig but often don't hit the 104 temp - lower it in desired airflow comensurate with the others?