HAZ-Matt

iTrader: (8)

This is something that has started now that it has been hot outside. Car is an 01 Formula A4 with LS6 H/C, 85mm MAF, LTs. With the AC on, I have been getting a dip in RPM and voltage when the fans switch to high at idle. At first I thought it was bogging when the AC compressor kicked on so I set the AC idle airflow limits fairly liberally but that didn't seem to do much. I then noticed that it really correlated with the high-speed fan setting. At any rate I returned most of that to stock and it seems a little bit better. I was really noticing the voltage gauge drop to right above the yellow section more so than the drop in RPMs, but the logs show that it does.

I was wondering why the high setting was kicking on since coolant temperature was way below fan2 enable temp, but searching the fan operation I saw a vague reference to the AC pressure affecting fan settings. So when I logged it today I decided to throw the AC pressure sensor reading as well as voltage into the otherwise standard idle config for HPT. Apparently the fans cycle to high when the AC Pressure sensor reads 2.78V, whatever that means, and then goes back to low when pressure is about 2.39V. I was able to capture two instances of the voltage dipping on my way to the store tonight, the first was more significant than the second. In the first instance the car went down to 502 RPM, from the set point of 550 RPM. The second was more or less when I arrived and the car was in park already so the idle set point was 650 RPM and it dipped to around 630 RPM and recovered quickly. The odd thing is that the idle speed and voltage drops are 4 frames in the log after the Idle Fan Air value goes up for the high speed fans. Looking at it myself I can't really tell what seems to be off when the idle drops.

I have a few questions:
-What output of the AC Pressure sensor voltage equates to what actual pressure in the AC?
-Does the computer command the extra fan air right before the fans kick on?
-What is it that is off and causing it to bog when the fan comes on?
-I cheated and used the Idle Fan Air value to indicate in the log when the fans switched, is there any good way to see when the AC clutch engages or disengages?
-And given the above is there a different set of parameters that would be more helpful for me to log to get to the bottom of this?

HAZ-Matt

iTrader: (8)

Here is my log on the way to the store and the config file I used. Sorry that it isn't just at idle, but I was in a hurry and figured I could get somewhat useful data at the stoplights on the way to the store.

edit: it doesn't seem to want to upload the cfg file. Basically as I said above, I added the PIDs Idle A/C Air, Idle Fan Air, Ignition Voltage, AC Pressure to that standard idle-airflow config. And the drops are at frame 5573 and 7932.

sixvi6-camaro

iTrader: (9)

Sounds pretty normal operation on a hot day with all the electrical equipment being run at once. the PCM commands the fans on high basically when the compressor is running. The fans have just a large draw when they first turn on combined with all the other electrical it strains the electrical system and causes the rpm drop. There are all kinds of settings that I've not messed with in regards to the fans on and off and AC system to compensate though. If your goal is to stop the idle rpm drop I'd start looking through the tables.

Old Geezer

iTrader: (3)

Battery condition is??

DirtyJohn

iTrader: (8)

Yes it does, just found this out myself after I was wondering why it was almost stalling out after sitting at a light.
Look at your "Idle | Idle Airflow | Cooling Fan Airflow | Fan 1 & 2" setting.

Might increase that to keep up with the needed air.
To eyeball how much I needed to increase it, I used the VCM controls to turn on the two fans and monitored STIT and how much it adjusted to catch up.
Then I raised that value that much.
Now it hardly stutters when the fans kick on at *207

HAZ-Matt

iTrader: (8)

Battery Condition is ok as far as I know. It is what was in it when I bought it a year and a half ago. It measured over 12.5V when I put a voltmeter on it with the car off :shrug: I guess I could get it tested at Autozone or something.

As far as the fan air, I am still curious why fan air switches to the fan 2 setting (0.40g/s from 0.15g/s) in the log several frames before the motor bogs. DirtyJohn, I don't know if your affirmative was just that the fan2 setting is commanded for hi-fan operation or that it always commands extra air a split second before it actually commands the fans to change speed. The reason I am curious about this is that I would have figured if the air setting was too low then it would bog right as the fans change speed. If the actual fan speed is commanded slightly after the fan setting changes then that would account for the 4 frame differences in my log, but otherwise I don't understand why there is that lag.

I need to take another look at the logs but what didn't make much sense to me was that STIT, spark, and LTIT seemed to basically stay the same after the fans went to high, except right during the RPM drop. After the spark and slight IAC correction to return the idle to 550 RPM, it seemingly went back to what it was before the fans turned on except for the fan air... meaning the STIT and LTIT at 550RPM with fan2 on after the bog seems to be the same as before the fan2 comes on at 550RPM. I might give fan 2 air another small nudge upward and see if that helps.

To be clear about the programming, I have edited most of the idle tables at some point or another. VE tables are mostly based on stock LS6 tables, as are spark tables. Base Running Airflow I dialed in using the guides and ran what I thought were optimized settings for that from last fall until now. I changed IAC steps versus airflow so that IAC Desired airflow is much closer to dynamic airflow. Obviously the temperature is much higher than what it was in the fall. TM is still intact which means that the AC torque calcs should be relatively close still.

Thanks for the help so far. Still curious about a few things including the what the AC Pressure Sensor output corresponds to in real pressure units (not that it is super important).

Old Geezer

iTrader: (3)

"Battery Condition is ok as far as I know. It is what was in it when I bought it a year and a half ago. It measured over 12.5V when I put a voltmeter on it with the car off :shrug: I guess I could get it tested at Autozone or something."

A fully charged batt should be about 2.2 volts/cell, for a total of 13.2V. AZ could run a load test. I'd also check to see what the alt is putting out, check all grounds, and check for charging volts at the batt. If charge volts is less than alt output, you may have a wiring integrity issue.