One tuning season is just underway. I am experiencing high BLMs with cold air temps. I see IAT temps at 65-70F at cruise and coolant at 186F or so. Before I had IAT control I had that table at 100% entire. Since environment temps are cool this spring is it wise to create a spring and fall specific tune? I presume I would reduce table % by 5%(?) accross the board or so to account for cooler than typical summer temps are.

 

ttt

 

I use a standalone system, but the physical properties are the same. You know that air gets more dense as temperature decreases, so you need more fuel to compensate. I normally see 100°F IAT's, and since that is where my fuel map was tuned, at that temp there is no change. Here is my IAT enrichment table that I calculated based on the density of air at different temps:



So, in my case, if I started seeing IAT's around 65°F, it would add 6% more fuel to the base fuel map. Hope that helps.

 

Thanks. Now I can run 2 .bins ....springfall vs summer....

Not so cold air... I think the joints made of syn rubber disallow the heat transfer to TBI. Prior AC was traditional chrome 14 inch.

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The other item that comes into play is the fuel composition. It varies throughout the year which makes an open loop tune move around. And the BLMs on a closed loop tune do the same.

I recall Grumpy mentioning that the more volatile compounds in the fuel can evaporate. This changes the tune as you drive or let the car sit for extended periods of time.

RBob.

 

Maybe I am missing something. I dont want to add fuel to VE tables. I want to change the IAT/coolant bias table. I INCREASED TABLE 6% but it had little effect.

I also at same time increased my BPC in the VAC/BPC in those areas I saw overrun (>100) in VE.

VAC/BPC is now Ok but I still see higher BLMs and it appears adding 6% to IAT/CTS did not make much of a difference. That table (gram/sec) would suggest a larger value of 255gram/sec means colder more dense air so the % of CTS shows a reduced amount there at 74% currently. At the other end I see 16 gram/sec which would be very hot incoming air at 100% of coolant temp. So to compensate more so for cold air I need reduce rather than add?

Did I move the table in wrong direction?

 

The CTS/IAT Blend table is the percent of CTS used. So a larger value is toward more CTS compensation vs IAT.

At higher airflow the table has lower values for less CTS% in the blend. The remaining % of the blend will be IAT contribution.

As an example, if the table has a 75% value in it. That means the blended CTS/IAT temperature will be 75% of the CTS and 25% of the IAT.

Then with the CTS at 200* F, and the IAT at 72* F, the CTS/IAT blended temperature will be:

200 * 0.75 + 72 * 0.25 = 168* F

RBob.

 

I think I understand? Now the next question is whether my IAT sensor and air filter is reading and seeing cooler air than what is present in a stock FBody? My sensor is attached directly in front/side of air cleaner on radiator fan support. I will assume it sees cooler air at all ambient temps than the stock FBody. If so, am I correct in reducing the % to bias toward the favor of IAT by REDUCING the %?

Example: (200F * .70) + (72F * .30) = 162.50F

That tells ECU it is a cooler temp and CU delivers more fuel dropping BLM.

 

Hi Ronny,

Reviving this thread. What did you end up doing with this?

 

Actually nothing. I used the stock EBL values and still are . I am not sure values are right for me as I have no heat to manifold nor TB. I was of opinion that I should tweek those values some to account for relationship of cold air(40dF) to A/F on cold start. My IAC is maxed at 200 steps. I was not getting rpm over 1000 on cold start 12.5/1 A/F). I reset IAC with routine and I think it helped as I now have a better cold start idle but still not over 1000 rpm. Maybe that table is OK stock?

 

Here I am two years later.. looking at finding those original values for the CTS blend table. They're all 100%, I can't find any data in this forum of what should those values be if you have the IAT setup. Any info?