Bunch of general tuning questions if someone cares to answer

[cerino2000]

I am pretty new to this and I have a ton of questions so if you happen to be one that knows what you are doing and don't mind answering, here goes (all relative to what I have learned or want to learn in my 96 LT1 Corvette:

1.) Can someone give me a definition on the term Hysteresis.

From what I can tell (relative to cooling fans), it dictates the amount of degrees in celsius that the car needs to have cooled off from the time the fan starts before it will shut off the fan. Is there a better way to define this in more user-friendly terms? I see it used in a few other places too.

2.) Under what conditions does the AIR pump run.

I see a threshold for when it is allowed to come on but what are the other conditions that dictate when it will be active. For example, if I go to WOT, is there something that says to never turn on the AIR pump under these conditions? How about in general cruise?

3.) When I go to WOT, I know that you will typically not be in OL. However, my DST shows that I am in fact still in CL but the LTFT's are at 0 during this time. So do you in fact go to OL during WOT or is it a different mode of CL?

4.) Assuming that you do in fact go to OL during WOT, is the table called AFR Vs. Coolant Temp Vs. Map what is used along with VE and MAF Calibration to determine how much fuel the injectors will push?

5.) If the answer to number 4 is yes, why can't I just go into that table and put in 12.5 for my WOT cells and be done. This VS adjustments to the VE table.

6.) Why would anyone make changes to the MAF calibration table. Seems to me that the MAF calibration is a matter of fact. Making changes to that seems like a bad thing. Assuming the MAF sensor itself is good, why in the world would you ever change the calibration of it. Changing it defeats the purpose of the MAF does it not? I mean, if properly calibrated, it will tell you exactly how much air you have coming in for the computer to make its AFR calculations. Take that exactness out of the equation and now you have lost a major variable that the computer needs to make correct calculations.

7.) IAC tables seem to be relevant to the term Steps. I am guessing that I don't quite understand how the IAC works. How are Steps relevant to the IAC?

8.) There are two tables relative to WOT in my case. One is AFR vs Coolant temp. The other is AFR Vs. RPM. So which one is actually applied or is it both? For example, if the AFR vs Coolant is 15% and the RPM is 8% is the final calculation The standard non WOT Value + The AFR vs Coolant % value + the correct value from the AFT vs RPM for a total of standard value * 1.23?

9.) Under what conditions would my car go in to SD mode?

I am sure I will have more and as I do, I will add to this thread.

Thanks to all that can answer any of these!

[rat]

Hysteresis allows the computer to use one set of readings on the way up, and another on the way down i think. Basically if you are fluctuating right around your fan turn on temp they will cycle on, off, on, ect. A larger hysteresis keeps it from doing that i think.

For PE don't you have a pe multiplier? Even if you have the afr tables that is not perfect. The computer may think it is comanding a 12.5:1 afr, but you may really have 14:1. Reasons for this would be differences in actual airflow vs. reported airflow via ve and maf tables.

Reasons for changing the maf would be for the above. Maf's aren't perfect by any means, and if you think the maf is off it may need to be re-scaled. I know when i put a full size truck maf on mine i put the full size truck maf table in my truck. But it ran like garbage, way lean, i had to bump the table up considerably. Many factors can play here, intake shape and geometry, maf sensor variations, engine characteristics, ect.

You should be open loop(not using o2 sensors) at wot, because the computer is commanding non stoich mixtures, and it can't measure those with the stock narrow bands.

Iac valves are stepper motors. You energize a set of coils in the motor, and the motor turns, and then it will hold to that step. If you have ever had a magnet on a table, and brought another magnet close, the one on the table will turn then hold. The computer extends and retracts the iac by timing what coils get power you can extend or retract the motor.

For your purposes big numbers are open, and small numbers are closed iac step wise.
There are some diagrams and such here: MegaSquirt-II Idle Air Control