Idle drops with A/C on

[jrc0210]

I have a 97 Camaro SS with a 24X ignition system running a 2002 0411 computer. I am in the process of fine tuning and can't get it to hold an idle with the A/C switched on. The engine has a 242/248 cam with a 108 lobe separation. The heads and intake are fully ported and polished and and is setup with a 12.1 CR.

I have attached a log file to show what it's doing, I have also attached my config and tune. As you can see in the log it will idle around the commanded idle but once the A/C is switched on it will drop to 350-400 rpm. I also held the idle around 1300 rpm and switched the A/C on and it will still drop 200-300 rpm. I have adjusted the A/C Idle speed to 875, I upped the A/C Offset max to 3.40, I zeroed out the A/C torque Max Retard, and nothing seems to help.

Any help would be greatly appreciated.

Thanks
John

My Config with AC Control.Channels.xml
AC Log.hpl
Tuning School Set Up Vac Leak WOT 3 AC troubleshoot.hpt

[dermotw]

Err I hate to say this but when that happened to me the AC pump siezed solid a week later, whilst I was trying to work out wtf was happening when the idle kept dropping..! Hopefully its nothing like that!

[jimmyblue]

Do you have the right kind of A/C pressure sensor for
the PCM? PCM is supposed to guesstimate compressor
shaft load and work back to an airflow adder based on
IAT and A/C pressure (and maybe some other stuff). It
seems like this is failing to happen. Look at the desired
airflow across A/C turnon event. Does it jump up, and
does actual airflow change to meet it?

Big cams whack the accuracy of low RPM airflow estimating
and it could be just this, too. Have a look at how your low
end of the VE table is set up (esp. the 400RPM column, which
you can't get data for, to fit - have to extrapolate "by eye"
in my experience, with a much less troublesome cam.

[dermotw]

You can log the actual reported AC pressure from sensor fairly accurately with this if needed;
Capture.JPG

EDIT: just looked at your log with it, AC pressure doesn't follow the "AC on-off" pattern, something wrong there.. but also, the A/F says 12:1 at idle? And the spark is up around 29 with AC off... too high (imho anyway...)

Too be honest, it looks like everything needs adjusting. MAF way too lumpy, VE not good etc...

[jrc0210]

Thanks for taking the time to look at my logs, I am in the process of tuning the car according to The Tuning School. The VE is running high and I believe its due to turning the A/C on, when I run the car without using the A/C all my VE numbers are less than +/- 5 from zero. I've attached one of my other logs to show how it runs (No A/C).

I will try load the A/C Pressure in the screen shot. How much should it rise? Looking at the A/C pressure volts in the log, it rises to at least 1.8v or more every time I turn the A/C on and returns when I shut it off, is it not climbing high enough?

I failed to mention not to pay attention to the MPVI.1 A/F readings, that system has been acting up which is why I put in the AFR500 (MVPI.2). I'm not seeing where you see 12:1 A/F, one never reaches above 11 and the other hovers from 13.5 - 15.

Also, keep in mind, this is an LT1 engine not an LS1 engine, everything I've read says the LT1 requires more timing than an LS1. Of course being new to the tuning world, I am open to recommendations to see how my car reacts.

Thanks again for looking
John

[dermotw]

Below, mine tracking AC (at the bottom, white line). It drops suddenly over at right because I stalled the car The range here is (in volts) between about 2 and 5, kpa pressure would go between something like 600-800 >> 2000+

The point where I stalled it, bottom point was about 1.7v, you can see what happens when I started it again...

Capture.JPG