Charge Temp vs. ECT under Cranking VE: What does it do?

[Tick]

just as the title states, what happens with the charge temp vs. ect table and why would it ever need to be changed? I'm tuning a car that has all kinds of stuff changed in terms of the cranking ve (basically cut in half), all kinds of screwed up values in the idle airflow settings, a zeroed out throttle cracker, etc.

I've put most of the stuff back to values that are stock based on other cars that I have tuned. However, when I put the charge temp vs ect table back to stock the car runs insanely rich at idle. I haven't tried to drive it, but its so rich that the short terms can't even get it in check....turn the trims off and it tries to idle at about 10:1 afr. If I put the table back to where it was the car runs fine for the most part.

The reason I'm still tuning the car is the fact that it starts up lean. On a hot start, it pegs my wideband at 16:1 but it starts pretty good. After maybe one minute when the fuel trims come on its fine....and if anything it will trim out a bit of fuel to maintain 14.7 afr. On a cold start, it doesn't always fire up the first try but it will fire up the second try and I never have to help it by giving it throttle. When cold, the afr registers but its still about 2 points leaner than commanded....if it commands 12:1 the car will be in the 14:1 range.

My quest to fix this issue led me to find the screwed up charge temp vs. ect table. With that table under cranking airflow, I can't understand how it affects the car while running?

On a hot start, the value in that table is 32 @ 194 degrees. A stock table has 19.1 in that cell. Whats really crazy is that in the 176 cell the current value is 0. The compare file has a value of 18.8....

I had a lot of trouble getting the car to lean up in the decel regions, but playing with the "min fuel milligrams" seems to have solved that issue. The car has 42 lb delphi/racetronix injectors.

Sigmon 18 is the tune with the screwed up values that runs, the final throttle cracker file is a compare file from a different car I tuned a while back.

Any help with my issues or insight on how the "charge temp vs. ect" table could change how the car runs long after it has fired would be much appreciated!

[outcastdon]

Interested also.

Stock values;
15.27, 15.59, 15.91, 16.22, 16.53, 16.83, 17.12, 17.41 17.70, 17.98, 18.25, 18.52, 18.79, 19.06, 19.32, 19.57, 19.82, 20.08, 20.33

All the stock square rooted kelvin numbers calculate either equal or over or under a fraction in comparison to the degrees in fahrenheit. I wonder how they came up with these? And if they are equal, why have this table? And as Tick stated, what does this affect?

[Tick]

I found something else out that blows my mind. I am a rookie tuner compared to most on here and I'm no engineer, but I have now tuned about 60 latemodel GM's. I'm tuning about 3 cars a week and learn about 5 new things on each one but this takes the cake lol.

I put the stock values back in the tune in the charge temp vs ect table once again as the car had several hours to cool. I started it up and again it was insanely rich. I glanced at the log and noticed that the iat's were near 300 degrees! Knowing that they should be around 60 degrees I changed the tune back to the screwed up values and guess what..... normal iat's.

Just to confirm i made sure the connector was hooked up solidly, wiggled the wires, etc on the iat. The value remained normal so I then flashed back those stock values and started another log this time without cranking the engine and again the iat reading was up near 300.

With the screwed up values in the tune I then did a log and let the engine completely warm up to 200 degrees with the fans disabled. Since the screwed up values jump from 0 to 30 or so at 194 degrees I thought the car might run bad once it became that warm but nothing changed. Normal iat's and the car runs fine..

I'm so confused I don't even know where to turn. Obviously I must leave the screwed up data in that table for the car to run anywhere close to right....I just wish I could make it start more crisp every time no matter what the temp. It also does seem to start better with the cranking ve chopped way down like it came to us rather than stock...

Heres a couple of log files. The one shows the high iats when the charge temp table is stock. The other is the idle log where I let it warm to 200 degrees with the screwed up data. In that log, you can see how the wideband is leaner than the commanded before the car goes into closed loop.

[GPGTP]

to answer your question solely based on the title of your thread. Not 100% on this but I'm pretty sure.

It's calculating the temperature of incoming a/f during cranking to compensate for evaporation. I would assume it's to get a correct target a/f ratio for startup, to get the burning going. In short it controls a part of cranking fueling.....I would leave it alone.

[Tick]

to answer your question solely based on the title of your thread. Not 100% on this but I'm pretty sure.

It's calculating the temperature of incoming a/f during cranking to compensate for evaporation. I would assume it's to get a correct target a/f ratio for startup, to get the burning going. In short it controls a part of cranking fueling.....I would leave it alone.

Did you read my post? I would agree with your idea of what it does....but on this car it clearly does more than just a little fueling during cranking. The fact that changing these settings changes the read out of the iat blows my mind. Maybe the pcm is bad.

I can't get this car to start very good at all when cold especially. It will start after maybe 5 or 6 seconds of cranking sometimes. Otherwise, I can crank for about 2 seconds with no start, then immediately key off then back to start and it will fire right up. It fires very lean on the first cold start despite the fuel trims being just fine once it goes to closed loop....and if anything its pulling fuel out once completely warm.

My natural reaction was to put these values back to stock (they were changed by a previous tuner I suppose) but when I did the car runs insanely rich and the iat reads about 250 degrees too high...

[LTstewy8]

The fact that changing these settings changes the read out of the iat blows my mind. Maybe the pcm is bad.

^THIS. If I set my "IAT calibration" as it should be, then the "Charge Temp vs ECT under Cranking" table goes whack, and vice versa. I noticed that if I manipulate the IAT calibration, it affects the charge temp vs ECT table in different ways. I'm forced to choose a normal IAT calibration because my car won't run if it thinks IAT's are 300 degrees. Is there a fix for this? Also, does the "Charge Temp vs ECT under Cranking" table affect a lean startup condition at all?

[LSxpwrdZ]

Sounds like something is messed up on that particular OS with mapping of memory locations?

Personally I would pull a 2002 file and overwrite the entire thing and start with the newer OS. You'll thank yourself later for doing so with the better idle control resolution and multiple tables. As well as IAT Temp Bias.

[GPGTP]

^THIS. If I set my "IAT calibration" as it should be, then the "Charge Temp vs ECT under Cranking" table goes whack, and vice versa. I noticed that if I manipulate the IAT calibration, it affects the charge temp vs ECT table in different ways. I'm forced to choose a normal IAT calibration because my car won't run if it thinks IAT's are 300 degrees. Is there a fix for this? Also, does the "Charge Temp vs ECT under Cranking" table affect a lean startup condition at all?

The charge temp vs ECT under cranking is only, as far as I know, going to affect cranking fueling.

[LSxpwrdZ]

If you open up the tune file Tick posted, edit the charge temp vs ECT table and close it. Notice it turns pink to let you know you have changed that table since the last time you saved it. Now open up the Engine Diag. tab and look at the IAT sensor calibration... It's also Pink, open the table up and you'll notice that the table is also edited.

[GPGTP]

This is something that needs to be brought to Bill's attention, if he doesn't already know about it.