((IAT PID)+(IAT2 PID)) / 2 = IAT Sensor

[CarsonTech]

This may have already been discussed, but after searching on the forum, I could only find 1 post about it, and it was't really discussed in detail.

Anyway, on the way home from work, which is a freaking 1 hour drive each way for me, I decided to log my sfts and lfts and compare them to my IATs. I just wanted to see how they would look in this 100+ degree humid weather when compared to a log when it was cooler.

I am pretty much stock, except for a K&N Typhoon CAI, 60# Injectors, and a 3.0 pulley.

My IAT2 temp got around 170 cruising!!!! I know, probably my HE pump or just because I am in boost alot more with this 3.0 pulley. I am going to check on my HE pump today.

When I got home, I reviewed the log. When looking at the Gauge Display in the scanner, my IAT2 guage matched what the IAT2 PID on the Table Display showed. BUT, the IAT guage did not match what the IAT PID on the Table Display showed.

When looking at most configs on the forums, and my own, I saw that the guage display was using the "Intake Air Temp" sensor instead of the IAT PID. After doing some math, I discovered that the Intake Air Temp Sensor reading is the average of the IAT and IAT2 readings.

Here is a pic so you can see what I am talking about:



Not sure if this info can be useful or applied to anything. I am using one of the Betas, 2.23.3793.23408 to be exact, if anyone wanted to know.

I thought some of you who might have not known this would find this interesting. I sure did. This makes me think about how the ECU uses the IAT Sensor reading and IAT PID reading. I read somewhere Chris (Of HP Tuners) stated that the IAT Timing Table uses IAT2 temps for adding or reducing timing. Then I read somewhere that those tables could actually use an average of IAT and IAT2 temps, just like the "IAT Sensor" calculates.

I guess the only way to find out is to zero most or all of the other spark "adder" and multiplier tables and take a log. I also read there is a IAT Retard PID in the, non beta, 2.22 scanner so we can see how much timing is being taken out at what IAT.

[S2H]

actually... you can use the IAT SAE pid...and build a table that relates to your complex clyinder charge table...
I actually make the x-axis read just the same as the bias temp table..and I make the y-axis read iat temp from say 70* up to 180* in 5* incriments,....

then youcan just do some driving around for a while...and let it log data...
when its all said and done..you can use the data to raise or lower the values on your bias temp table...if it gets leaner as temps go up... then you need to increase the values in the bias table... if they go leaner, then you need to decrease the values...
at some point you will see it level off somewhat nicely.....

downside is that it takes lots of long logs... and you have to retune the VE(with filtering to stay within a certain IAT range) as you go for the changes... then do another long log...and look at the data again...

best to do the whole thing using a wideband as your fuel trims take too long to update and will give you a false impression of what is actually happening due to the lag time

[CarsonTech]

I wish these cars had complex cylinder charge tables to mess with. Unless I am missunderstanding your post. The only IAT correction I know of, with the supercharged LSJ ECU and OS's, is for spark and boost limiting. I found this odd, as I came from 3 LS1 cars, and expected some type of correction for airflow.fueling depending on IAT for my Redline.

The only thing close to this I could think of is using, if I was operating in openloop, is the IVT table, but I can't figure the exact formula out for how the ECU calcualtes IVT. I like closed loop with VE/MAF anyway, though, I just thought it would have been cool to figure out some system for correcting airflow/fueling with IAT.

[gmtech16450yz]

Sorry if I'm wrong, but I think soundengineer has more E38, E67, E40 experience? The LSJ and LNF tables are severely limited compared to those ECM's. I was used to E38 stuff, when I first looked at my LNF in HPT I was like "Where the h*ll are all the tables?".

I noticed the same thing you did about the 3 different ways to log IAT, you're right, it seems like using the IAT sensor instead of the pid seems to show an average of the IAT and IAT2 pids. I also noticed this with KR, you can log Knock Retard, Total Knock Retard and the sensor Total Knock Retard, (that also shows as "Timing Retard"). The Total Knock Retard sensor appears to be an average of the two pids Knock Retard and Total Knock Retard.

Maybe this is a very basic question that I should have known log ago, but do we know which one of the three the ECM uses for say timing control, in the case of KR? On the E38's it's very easy to see what is retarding timing, and exactly how much. But in the LNF OS it's kinda hard to see timing changes in relation to KR. In the E38, if it shows KR is retarding the timing 5 degrees, you'll see the actual timing drop 5 degrees at the same time. On the LNF when it shows 3 degrees KR, even at steady throttle and rpm, you might see it drop, or stay the same, or even go up sometimes. Not nearly as clear to see as it should be, it's made me wonder if 3 degrees KR on the LNF is even actually retarding overall timing at all. ???