I typically see 11.6 on the WB when it's 50 degrees and below. 60 degrees and higher will give me 11.1 and along with the boost drop.

Is everyone else seeing the same changes of A:F with temperature?

 

I used to see it most frequently with an MBC since the higher boost was disproportionate to the load cells I was in and the ECU couldn't regulate it.

Obviously the air density is higher so the load cells are slightly different, either your in cells you haven't tuned before now, what I mean is if your load was 240 then you were square in the 240 cell, but if its 248 you'd be closer to 250.. Look at the adjustment of your adjacent cells as thats the first place I look. Injector scaling, coolant temp, air temp, etc all come into play on cold days..

I'm actually surprised its a little leaner simply because the denser the air, the higher the MAF reading, and higher load you'd ultimately register..

 

Or the loads are nearly the same, so hes staying in the same load cell, but actually bringing in more air. Remember the MAF reads air flow and not air density.

This could explain the lean conditions

 

thats right, kaarman reading is only slightly less

But whatever it is, less boost, less air, less o2, more CO and CO2 - there is a big difference in power and somewhat of a difference in IPW/load (I found to be same thing lol) like 2.10 seconds or 2.30 seconds 4K to 6K




I think EcuFlash might have something...

 

I was simplifying things a little, there is an air intake temp sensor so it does actually use that value to calculate air density.. Who knows WHY its doing what its doing though.

 

I think UCB may be on the right track. MAF has to be corrected for temperature, if that correction factor is off, you are likely to see a lean or rich shift at 10 or 20 deg increments.

In this case, it would be under correction, since colder air is not being matched with enough fuel.

-jjf

 

Well I figure since my AFRMAP values and Airflow values differ very little between the two temps that my MAF needs recorrecting - thanks

Now, how do I do that

 

I see the same behavior on my Evo. I assumed it was the MBC running more boost in cold weather (which it does), but forgot about the fact that this should simply put me in a different load cell and the ECU should compensate.

For whatever reason, the trend seems very clear though: colder weather == leaner by up to 0.3-0.5 or so.

 

THATS EXACTLY WHAT WAS LOOKING FORWARD TO HEARING!

Thanks Rob W

I just thought 0.5 was quite a bit, I guess not

So here is how I see it, there are two factors, colder denser air produces more boost due to more energy per unit/vol (O2), air volume is more laminar as well so the MBC which feels static pressure more than dynamic (laminar), won't compensate for the larger vol of air.

The second factor is at colder temps more O2 passes by per hz of MAF output

What else

 

What is your injector duty cycle in warm vs. cold weather? You could, in theory, depending on what kind of boost you are running/injector size/fuel pressure/fuel pump, be maxing out the fuel system, causing it to run a little leaner because you might be right on the threshold.

You would not see this problem in warm ambient temps(if you were over 85% duty cycle in warm temps), because your duty cycle would be lower from the less dense air, but once the temp falls and the fueling needs increase, depending on the above mentioned factors, your fuel system might not be able to compensate phyically for this, no matter what the ECU tells it.

I have seen this a million times while tuning.

CJ

 

The ECU already calculates an air mass or air density. So, the theories being mentioned here are somewhat incorrect. This is why our MAF housing also has a baro and temperature sensor to provide data for these calculations. I actually used them to calculate air density in LogWorks.

I know there are temperature compensations tables in the ECU, so this may be part of the puzzle or maybe not. Obviously, as Jack stated, moving around in different load cells would also cause different fueling, but I see that at least one person in this thread was in the same load cells. I wonder how this was determined? We know that calculated load is not that accurate. Perhaps a better test would be to set a block of numbers in your fuel map and test again?

Another possible thought could be that an aftermarket air filter or intake setup alters the airflow reading, causing an error in actual air mass caluclations by the ECU. This error percentage would have more of an absolute error the more mass airflow that you are flowing, such as during colder weather.

Just a few thoughts thrown out there. I just wanted to make sure that everyone knew that the ECU does already calcuate a mass air flow and air density, so temperature differences should have no effect. The only change in fueling would be if (1) you hit different load cells, (2) there are extra temperature compensation tables in the ECU, or (3) your air metering is already off and being slightly exaggerated the more mass airflow you flow.


Eric

 

I see the same variance of .3-.5 leaner in temps lower than 50F* and run stock airbox with drop in filter.

 

Do you guys have this table in your ECU definition in ECUFlash?

I think this was already in mine. It is under fuel and called Air Temperature Compensation. Perhaps you could experiement with it to see what it does?



Eric

 

Mine looks exacly the same.

 

Thanks,

I will do a log during lunch, should be 55F outside, I just did a log before work at about 80F. I will compare the two as standard and exp.

Then after the pull I will flash an air temp compensation change to the ROM where 50F units equal 82F units (wow, my ROM is listed as C but the values correspond with F). I will do a log cold (tonight) and tomarrow afternoon should be beutiful (not for turbo cars) so I can log a 80F run.


Another factor thats probably exasterbating the problem is the air guide I have fitted at turbo intake. It basically provides an equivalent reading at the MAF with 2 psi less manifold pressure