Folks, Steve is raising a great question and one that all the VEC3 and newer model owners will have to contend with. But to bring everybody along, allow me to give a little background on Steve's question..
IAT = Intake Air Temperature, and as many of us know already, when the temperature of your intake goes up...the air inside expands. If your air expands
and your fuel remains the same...you end up with an overly RICH mixture
. That means too much fuel being added to too little air. As you might imagine...in cold temps, the air compresses and, therefor there is more of it...keep adding the same amount of fuel and, yep, too much air and not enough fuel...a LEAN mixture or one without enough fuel is created.
The VEC3 has a new software screen added to it. Its a new and important one and sue beats
having no ability to account for temp changes. It looks like this.
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This new program allows us to potentially add one last adjustment before the final calculations that drive the fuel calc signal is sent to the injectors. Simply put, this is a temperature scale, one that allows for
more or
less injector seconds to be added based on
the IAT (Intake Air Temperature).
Now Steve's logs show a real requirement to find a way to properly account for the differences in air temperature as his car is driven in everything from pretty much freezing temps to over 100 degrees. He knows that his car's
wideband logs are showing and
Air-To-Fuel (Lambda...in his supercharger is approximately 11.7-11.9) that is way too lean as he ran his car in colder temps.
The details are as follows:
On May 22, 2007, Steve took his car out when the outside temp was 76 and the intake was running at a pretty constant 96 degrees. In other words his IAT was...96 degrees.
He did his run and found that his A/F was running fairly flat at about 11.5..not too bad. But he wants the target 11.9, so he slightly reconfigured his VEC3 fuel tables.
On June 8th, 2007, out goes Steve again for some logs. The outside temps were
cooler coming in around low 60s with his AIT reading a
lower 68-82. His log showed that his air/fuel was now too LEAN...way too lean, just what one might expect. But his numbers required some real attention.
Excellent at 96 IAT....too lean at 80 IAT...So now the question being asked is have any of us worked with the IAT tables to see if we can get it to properly alter the fuel pulse to compensate for the temperature changes in the intake..
Steve,
1. The temperature range of the VEC3's sensor is very precise and encompasses a temperature range that the engine will never actually see. Sean told me this and when I realized this, I tried a number of different things. You have already mentioned that " I'm finding that 10-15% each way may be end up being the target. I started at 4% each way" "
So that everybody is with us, that would result in a VEC3 table that looks like this.
A 4% each way table would look like this
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A 12% each way table would look like this
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When I realized that the scale of temperature ranges was far greater than my car would see
I decided to change the slope of the curve by bringing in the sides...
Now, I still working on this because
here in CT we havent had great temperature changes yet. but
this is what I am currently experimenting with...
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Have you tried changing the slope so it creates a much greater reaction? I need some really hot temps out here to be sure. I still havent got the table to 86 degrees yet because, so far, the A/F numbers (in my limited temp range) are still looking good with no peaks above 12.4 on a warmer day. Steve, it doesn't get colder here now!
I have not shared any of this with Sean yet, so take it with a grain of salt.
IN OTHER WORDS, PROCEED WITH CAUTION AND DO LOW RPM LOGGING. I literally drive around with my best card and have some new IAT cards that I run just long enough to log at this point.
Hope that helps!!