Hello All,
About me: I picked up a 01 C5Z with all bolt ons, heads, and cam (MS4) a while ago and had it tuned. There were some startup issues I was having and AC issues as well. Rather than driving all the way back to get it retuned (3 hour drive one way), I bought HP Tuners and decided to mess around with tuning for the LS platform. Now, I may be new to HP Tuners, but I'm quite experienced with tuning on the other side of the car world. I have a supercharged 09 Civic Si as a daily that I have been tuning myself for about 6 years now.
Abstract: I found that when I tried to learn HP Tuners, a lot of the tables were not intuitively named and it was kind of confusing what exactly the tables did. My AC compressor seems to be slowly dying and has an increased load on my engine, causing startup issues and idling issues. Me trying to save some $$ now, figured i could use this as a reason to jump in the tune and tweak things.
I did not find much information making about how to tune startup airflow or AC airflow, so I'll highlight some of the things I learned below to hopefully help any other newbies like me.
Startup Airflow:
Under Engine > Idle > Airflow, you'll see some tables under the "Startup" section on the left:
Screen Shot 2015-05-26 at 6.46.55 PM.png
Here are the tables/values and my description of what they do (at least as far as I observed):
Off Idle Scalar: This is used when your car has just started and is still using the startup airflow tables, and you do something to make it leave idle conditions (this could be pressing the gas pedal at all, or moving the car, etc. Anything that is not idling). The value ranges from 1 to 0 (and anything in between). A value of 0 means that if the car is using the idle airflow tables and something happens to exit idling, immediately stop using the tables (all airflow table values are immediately stopped from being referenced). A value of 1 means that even if something happens to exit idle conditions, continue using the startup airflow tables as normal. A value of 0.5 would mean to keep using the airflow tables, but use half of the value thats in the table. In my car, it is set to 1, and I decided to keep it that way, because I want the car to add the additional air shortly after a startup regardless of what i'm doing.
Underspeed Time: If startup overspeed flare has not occurred within this amount of time, then enable adaptive idle. Probably fine to just leave this alone, it doesn't particularly affect startup airflow or AC.
Friction Airflow Initial:I'm starting with this table, because it makes the most sense to. Friction airflow is additional air that gets added to your desired idle airflow during the first few seconds after startup only. Cars typically require a little extra air when they get started. This table describes how much extra air (per ECT temp) gets added. Friction airflow starts at this value, and then will stay here for a certain amount of time (defined in friction airflow delay) and then will decay to 0 at a rate defined by the friction airflow decay table.
Friction Airflow Delay: This tells the ECU how long to keep adding this extra air after startup (in cam revolutions) vs ECT. IE, if ECT is 198F and at that cell, it says 5. That means that the extra air will be held at a stable value from the frictional airflow initial table for 5 cam revolutions before it starts to decay to 0 g/sec. For a reference, a 1000 rpm idle has ~8 cam revs per second. so 16 cam revs would be about 2 seconds.
Friction Airflow Decay: This describes the ramp out rate of the friction airflow. Higher values correspond to the extra air ramping down to 0 in a shorter amount of time. Lower values correspond to a slower ramp down to 0.
Friction Airflow Graphic:
The below graphic illustrates an example of what the ECU does with the values from these tables. Keep in mind that normally the cam rev delay is so low that this entire process takes place in less than a second. (You can log this PID in Scanner)
FrictionAirflow.jpg
Startup Airflow Initial: Very similar to Friction Airflow above, except that this normally takes place over a longer period (IE ~10 seconds or less) with higher delay values (50 to 100 cam revs). This is intended for the slight increase in air required by a car when it first starts.
Startup Airflow Delay: Same thing as the Friction airflow delay, except that the values typically are larger to last for several seconds. For a reference, a 1000 rpm idle has ~8 cam revs per second. so 16 cam revs would be about 2 seconds.
Startup Airflow Decay: The decay rate of startup airflow once it hits the delay value. Higher values mean that the additional airflow decays to 0 faster, and lower values slow the process down.
Startup Airflow Graphic: Below illustrates the startup airflow process and where the ECU gets the values.
startupairflow.jpg
Things to note about Startup Airflow and Friction Airflow: They are additive! This means that the ECU adds them all together on top of the base idle airflow (RAF) table to get the desired airflow for startup. The friction airflow is supposed to be very short to compensate for the fact that no air is flowing, an there is extra friction in the intake manifold during the first second of startup. The startup airflow is designed for the slight increase in airflow needed by the engine during a startup before it will settle and require only the value in the RAF. So don't just duplicate values into both the startup and friction airflow tables, because you will essentially double what you put in one needlessly.
How to tune startup airflow: Normally, you don't need to touch Friction airflow because stock values should be ok and it's just a short transient. If you did the proper RAF tuning and find that when you start your car up, it still stumbles a little bit (commanding higher STITs when it first turns on and then the STITs fall to 0 somewhat quickly), this could be a result of not having enough startup airflow. In this case, I would open the Startup Airflow Initial table and increase the airflow values (check to make sure the units are what you are expecting by right clicking on a cell, going to units, and selecting the appropriate unit. I prefer g/sec. To make my car happy, it seems to like 2-2.25 g/sec throughout the ECT range. Tweak this value until you find a point where the car doesn't stumble any more. I would log the idle startup airflow PID and watch a startup process when the car stumbles. If the idle startup airflow starts to decay to 0 too soon, you can increase the delay values (remember that 8 cam revs = ~1 sec). If the airflow ramps down to 0 too fast and causes hesitation when this happens, you can decrease the value in Startup Airflow Decay to make this ramp out process slower.
AC Idle Airflow
Please see post #2 as I can't add anymore pictures to this post, I need to make another post.