Idle settings with AC on - Megasquirt help

[E9Wayne]

Hello SFdon or others experienced with managing idle with Megasquirt and AC on. I finally have operational AC after about 3 years of fiddling and component upgrades.

My issue now is the idle drops too much (practically stalling) when the AC kicks in at idle.

@ SFdon, I forget how you set up my idle control valve to operate with AC and Megasquirt and you already had me adjust my mixture and ignition advance last year which helped avoid stalling out.

But the attached seems a simple way out of this: if I adjust the idle advance settings to engage when idle drops below, say 800, wouldn't this solve my problem? Any input on what these other settings should be adjusted to also: TPS, load, etc?

Thanks all and I hope one day we all have a rich Megasquirt library on this forum for folks like me that are fine tuning this wonderful engine computer!

And see everyone in monterey in a few months! i'm working through a long punch list of repairs, etc. for this special trip

 

[Sven]

Wayne,

If you turn this idle advance feature on it will only take you to a load/advance table. i.e., you can focus in on a smaller area of the larger spark table for finer resolution (similar to the Idle VE table) where you have load on one axis and advance on the other. This might help a bit, in that you could set the load range so that for non-AC operation idle advance it at one setting, then when the AC kicks on the load goes up and you set the idle advance higher for that higher load.

Another approach is to set the base idle higher so any additional load still keeps the idle above stalling.

I don't recall if the MS2 has this table. I use this feature in MS3. When AC kicks on it will idle up by a certain rpm and open up the idle valve a bit. It can also turns off the AC if you go above a certain WOT load (for more power when you need it accelerating hard).

 

[afeustel]

Hi Wayne and Sven.

Funny that I was just looking at this idle advance option 2 days ago and chatting with Don (because we are seeing nearly 100F temps here in Houston). Sven, the MS2 that Wayne and I have does not have that IdleUpScreen option (at least mine does not).

Wayne, I looked at the same idle advance screen that you did and decided I did not want to mess with the advance settings because then you would probably have to mess with the VE table as well at those loads to get the AFR correct. To be honest I did not try it.

What MS2 does have is an internal analog wheel variometer (for Idle Kick-Up) that is supposed to trigger from a 12V signal to the box on pin 40 (IRRC). Unfortunately my MS2PNP analog wheel does not appear to be working since I cannot get the idle to do anything different with the A/C (pin 40) trigger set and varying position of that wheel.

I ended up setting the idle so that with A/C off the car idles at around 1100 and with A/C on it idles at around 900 while still maintaining 13.1 AFR.

The other option is Closed loop idle (Sven I think you use this). I've tried previously to get the PID settings correct on this but did not quite get it tuned correctly. I may try again now that I have a good steady set up with Open loop.

Drew

 

[sfdon]

Set your idle at 1100 and AFR at 13.2
Early MS was lousy at AC
You can install a AC solenoid on the bell crank..

 

[vraned]

I set this up on my MS/2 v3.0 board, running MSExtra. Don convinced me to upgrade to MSExtra firmware and the A/C Idle-up was one of the features that were included. It took a couple of tries to get the circuit right. I tapped off of the AC compressor switch, dropped the signal down to approx 10vdc through a 2.5k-10.18k voltage divider, mostly for current limiting, and then fed that into the gate of a transistor in the proto area. The collector of the transistor is tied to JS7 and normally held high (5vdc) through a 1.2k resistor going to the 5vdc source in the proto area. The emitter is tied to ground. With the AC on, the transistor drives JS7 low. Running the PWM idle air valve in open loop, my AC Idle-up settings are as follows in the Startup/Idle>Air Conditioning Idle-up>menu:
A/C Idle-up: on
Idle-up Output: off
Idle-up Input: PE0/JS7
Idle-up polarity: Low
Idle-up delay: 200ms
Idle-up min RPM: 300
Compressor delay Since Last On: 5s
Idle-up Duty Adder: 7.4%

It works.

 

[E9Wayne]

thanks everyone, but...

I will consider the rpm bump and AFR but does anyone know what would happen if I try this Idle advance settings menu with some basic parameters (low TPS, rpm drop below 800, warm engine temp, etc.)

Don, the AC solenoid approach - have you done on other cars and, if so, I take it this works?

Perhaps I consider MS3 upgrade down the road if the problem doesn't get much better. Don was also telling me start up sequence is much smoother too in terms of less engine cranking...

thanks, E9 colleagues

 

[Ohmess]

Hi Wayne -- Stevehose did a solenoid mounted near the bell crank that bumps the idle whenever his a/c is on. It is a simple setup using an electrical signal to trigger a plunger that basically moves the stop point when you let off the gas so that the idle goes up. If I remember correctly, it uses the same a/c fan switch signal to initiate the idle increase.

Steve and I both have carbs, but I think this setup might work in your car.

I have the detail on Steve's setup somewhere (part number for the solenoid, wiring, etc.); I am hoping to replicate it if I ever get my various new a/c parts connected to one another. (Which, of course, I would like to do before we jet up to the PVGP).

 

[Stevehose]

http://www.e9coupe.com/forum/showthread.php?t=12691

 

[Sven]

Wayne - here is another solution that might work for you. I used this back in '08 when I first started messing with MS and they did not have AC control yet. This valve came on my 735i donor engine. You connect one hose to the small port on the throttle body before the butterfly, then connect the other end to the manifold log. There is usually an extra port or two on the log. The valve is open by default, so you have to have 12v on to keep it closed. I tapped the AC compressor wire. Ran this wire to 85 on the relay, 86 to ground, 30 to 12v battery, and 87a to the valve. So when there was no voltage on the AC line there would be 12v to 87a (keeping valve closed). As soon as AC line came on, the relay would switch to 87 thereby disconnecting 87a and opening the valve. This bit of extra air provided by the valve bumped up the idle enough for the AC load.

I had the valve under the idle valve attached to the same stud as the idle valve.

I am not sure how it would react with the newer PID idle control these days. It is probably easy enough to test. Connect a 4 ft hose to the air plenum and take the other end into the cabin with you. With engine running and thumb on the end of the hose, turn the AC on then let air into the hose and see what happens.

 

[E9Wayne]

great input!

Thanks, Sven, Steve and Chris. I may try this out if I can't get the super smart MS brain to do this for me. Chris, maybe this will a project for us post Pittsburgh and Monterey?