How does weather effect your fuel trims???

[scv_guy]

I have been trying to dial in my fuel trims on my 2010 Camaro, I notice if I log the car in the morning (70 degrees) the LTFT are good (-1 or -2) but If I log the car in the afternoon on the way home from work (95 degrees plus) I'm seeing LTFT of 3.5 - 4.7?
Is this normal?

[schpenxel]

Similar here.

What are you IAT's in the morning vs. afternoon?

There is an injector flow rate vs. IAT multiplier that others have used to help with this

[scv_guy]

There's a good 30 plus degrees difference between morning and afternoon.
Being im very new to tuning, is it better to tune it one way (morning for example) and leave it alone? I feel like im chasing my tail.

[schpenxel]

Safest way is probably to tune it for whichever is leaner (i.e. afternoon) and then you'll just be a bit richer in cooler weather.

[seven ends]

Similar here.

What are you IAT's in the morning vs. afternoon?

There is an injector flow rate vs. IAT multiplier that others have used to help with this

Great tip!

To richen up do you:

A) Less than 1.0 the IAT value to make the injector look smaller or
B) More than 1.0 because the multiplier is applied after ECM sizing?

[Higgs Boson]

Great tip!

To richen up do you:

A) Less than 1.0 the IAT value to make the injector look smaller or
B) More than 1.0 because the multiplier is applied after ECM sizing?

he is saying calibrate the MAF/VE when it's hot out and you should be good for cooler air as well. same thing with spark, imo, set it when it's hot out.

[seven ends]

he is saying calibrate the MAF/VE when it's hot out and you should be good for cooler air as well. same thing with spark, imo, set it when it's hot out.

Thanks, that is what I have been doing to date. What I have not done to date is capitalize on the flow rate IAT multiplier to tune less swing, I have been leaving it 1.0 across. I am asking where it comes in at relative to ECM determining size, meaning does the multiplier work by making the injector look smaller or larger or does it apply after the ECM has determined the sizing from the base flow rate table????

[seven ends]

I think I found my answer at the bottom of this old thread. cheers

http://www.hptuners.com/forum/showth...odifier-vs-IAT

[Eaglegoat]

What you guys want to tune is your bias tables.

Unless your dealing with some ridiculous temps, like death valley hot to Antarctic cold, you shouldn't need to mess with the IAT multiplier.

Remember density is determined based on absolute temperature. So your 30 degree swing is at most a 10% temperature difference. That doesn't translate to a 10% density difference closer to 2%.

Fuel is much more stable than air as far as the density goes. By tuning the bias tables you are fixing how the PCM estimates charge temperature. To do this your VE take must be tuned nearly perfectly under beer controlled conditions. This can take quite some time if you're tuning on the road.

[GHuggins]

Which way do you personally move the bias for this. Are you just moving it the percent fuel trim that's being thrown off and in which directions for rich or lean?

[seven ends]

Below in italics came from a reply I got from Greg in to 2008 to a post on a Gen III. In the early days part of the suggested tuning process was to put 1.0 across in the bias table to keep it from changing things while you were logging and updating. When you put any other numbers back in there (like return to stock) the tune went a little to hell. I was also concerned about what a swapped in 160 thermostat was doing to me. What I take away from Greg's reply is that as long as everything is in the stock position then GM has already modeled this in to the numbers and probably in a lot more sophisticated manner than I am capable of.

The biasing is there to model how much the measured air temps (from the IAT) get warmed up as they pass through the intake and heads (which are assumed to be at/near measured ECT temps) on the way to the cylinders. If you run a cooler thermostat, there will just be less heating of the aircharge due to the lower temperature differential between the two. The factory biasing strategy already takes this into account and should just work as long as the IAT and ECT sensors are in the same place as stock.

http://www.hptuners.com/forum/showth...ature-Bias-ECT

But you are right for "my current setup" I need to do something for bias because my IAT reading comes from the manifold of the blower instead of the MAF, the IAT flow rate multiplier just looked like it had more straight forward possibilities. So I am in for the next step as well and beer if available.

[Eaglegoat]

Which way do you personally move the bias for this. Are you just moving it the percent fuel trim that's being thrown off and in which directions for rich or lean?

That's as good a plan as any. Let me know how it turns out.

I personally usually leave it. Unless there's a major change in intake length or style. Like when putting a Maggie on I'll bias to IAT because of where it moves the sensor.

The swings aren't big enough to worry about IMHO, so I don't. I also don't tune with the fuel trims. Ever. Narrowband o2 sensors are far from scientific equipment. I use only information from my wideband. I recommend using filters to narrow the data used, this will help limit variables.

Empirically, once you've finished your tuning doing it this way you'd be able to change the bias tables to account for temperature dependant variation, after eliminating other variables like fuel composition.

Below in italics came from a reply I got from Greg in to 2008 to a post on a Gen III. In the early days part of the suggested tuning process was to put 1.0 across in the bias table to keep it from changing things while you were logging and updating. When you put any other numbers back in there (like return to stock) the tune went a little to hell. I was also concerned about what a swapped in 160 thermostat was doing to me. What I take away from Greg's reply is that as long as everything is in the stock position then GM has already modeled this in to the numbers and probably in a lot more sophisticated manner than I am capable of.

The biasing is there to model how much the measured air temps (from the IAT) get warmed up as they pass through the intake and heads (which are assumed to be at/near measured ECT temps) on the way to the cylinders. If you run a cooler thermostat, there will just be less heating of the aircharge due to the lower temperature differential between the two. The factory biasing strategy already takes this into account and should just work as long as the IAT and ECT sensors are in the same place as stock.

http://www.hptuners.com/forum/showth...ature-Bias-ECT

But you are right for "my current setup" I need to do something for bias because my IAT reading comes from the manifold of the blower instead of the MAF, the IAT flow rate multiplier just looked like it had more straight forward possibilities. So I am in for the next step as well and beer if available.

It's not bad to assume that GM did a good job. But they also develop a MAF table that I've never seen be perfect in a completely stock vehicle either.

[schpenxel]

I have the IAT sensor in the intake manifold and still have the same problem with it going leaner at higher IAT's. I'm sure the bias table could be used to fix it, I just haven't had much luck messing with it.

[schpenxel]

Great tip!

To richen up do you:

A) Less than 1.0 the IAT value to make the injector look smaller or
B) More than 1.0 because the multiplier is applied after ECM sizing?

Less than 1 = computer thinks injectors are smaller, meaning it will INCREASE the injector PW. This will add more fuel

Greater than 1 = computer thinks injectors are larger, meaning it will DECREASE the injector PW. This will remove some fuel

[Eaglegoat]

I have the IAT sensor in the intake manifold and still have the same problem with it going leaner at higher IAT's. I'm sure the bias table could be used to fix it, I just haven't had much luck messing with it.

Did you adjust the bias table for where you moved the sensor? Are you sure the sensor isn't heat soaking?

[schpenxel]

Did you adjust the bias table for where you moved the sensor? Are you sure the sensor isn't heat soaking?

Bias/filter tables are setup like ZR1's are. One of the tables is set to 1, the other to 0. Can't remember which is which offhand

Basically IAT=Manifold air temp in this config.

Quite possible it's heat soaking