Huge difference in cold and hot weather?

[a1320eclipse]

Check my profile for mods. But... im haveing to completely readjust settings an my safcII for coller and hotter weather, should i have to do this? during the day its been getting around 85 degrees or so and at night it drops to about 60 ish. im having to make huge changes in %of fuel. Also, friday night i just got my downpipe hand made and the car was nuts fast, and half way through the night it just kept getting slower and slower and now thet car just runs good according to the nubers on the logger, but its noticeable slower. im pulling my hair out here, anyone know of anything?

 

[spyderturbo007]

It depends. When things get cooler, the density of the air increases. This will cause your airflow to increase, based on the temperature change.

Why are you having to adjust your tune every day? How much of a difference do you see between the 85 degree tune and the 60 degree tune? What is the change in your airflow?

Mine airflow normally increases by about 1 - 1.5lbs/min every 10 degrees or so. I don't have a thermometer in the car, so the temperature change is just an estimate. Anyway, it's not enough to significantly effect my tune.

 

[daren_p]

Am I off here or shouldn't the temp sensor in the MAS measure these differences and adjust the amount of fuel automatically to compensate for the changes in outside air temp/air density? So you tune should keep pretty much constant, is it possible that the MAS is no good?

 

[bfdahl]

well, welcome to dsm tunning, its depressing some times but when you have all the tools to see exactly whats going on with the engine you can see how close to the edge your tunning can be, and how atmospheric conditions affect cars!

on my tune now, my car runs abit lean on the way to work and on the way home when its hotter in the day it will have amost no knock and run great.

today well are having huge humidity in LA and things will need to be adjusted today as well!

usually ill just turn the boost down abit while im doing the daily grind

 

[spyderturbo007]

Am I off here or shouldn't the temp sensor in the MAS measure these differences and adjust the amount of fuel automatically to compensate for the changes in outside air temp/air density? So you tune should keep pretty much constant, is it possible that the MAS is no good?

Hummmm..........Not sure on that one, you might be right. My initial though would be that it doesn't correct for the fluctuation in temperature because the IAT is before the turbo, intercooler, etc. That means that the ECU would have no idea what the final temperature of the air turns out to be.

That and that fact that I have seen changes in my logs with no other variable than ambient temperature. But I guess there could have been something else involved.

I think I might have to do a little poking around on this one.

 

[daren_p]

As far as I know the ecu doesn't have any idea of what the final inlet temp is at the TB, and all the calculations for fuel/timing are done pre turbo, ic, at the MAS. The MAS needs air temp to calculate the amount of air entering the motor so it would seem logical that it adjust the fuel for changes in inlet temp. Yes you can see differences in your logs just because of ambient temp changes, obviously cooler air is denser, making more power with intake temp but you also have to take into consideration the outside air temp will also directly effect IC operation. The cooler the ambient air, the greater the cooling effect of the ic.