I am making a harness cable for my v2.2 MS and had a question about how to hookup the BAC.
Pin 30 goes to 2Q, which is the gnd for the BAC, but for +12v, I also need to jump 1C to 3I on the car harness side, right?

3I is constant 12v from the fusebox isn't it? Does it matter if it's constant or should this be something hooked up with the fuel pump relay power?

 

Pin 1C is the low (ground) side of the air bypass relay. Totally unrelated to the BAC, and should not be connected to 3I. The air bypass relay is what makes the engine run at 2500 RPM (or whatever it is) for 20 seconds or so when it first starts. I haven't head of MegaSquirters using that feature.

Pin 3I is switched by the ignition switch, and in the factory harness also powers the high (12V) side of the BAC. Pin 2Q is the low (ground) side of the BAC, and is controlled by the MS.

 

If you're using the stock harness, the BAC should already have +12v being supplied to it, so you just need to replace the Fidle transistor with a ztx688 or ztx689 (I prefer the 689), and hook up the "ground" wire of the BAC to the fidle pin on the MS, then set up the megasquirts PWM idle settings.

eagle7: my plug 'n play units all control the BAC valve... and tofuball and I have been controlling his with the MS almost since the beginning... some slightly out-of-date info on it is in the FAQ.

 

Okay, thanks guys. I was looking at the wrong part of the FSM after I got my terms mixed up.

 

Can we get some "up to date" settings for the BAC using the current firmware?
Would really be a big help.

 

Yes, I'm using it too. I was saying that the air bypass relay is not commonly used. It's a shame that Mazda (or whoever) used such similar terms for different components.

 

I have nothing posted in the FAQ for settings. All you need to do is set up the Fidle circuit as if it were a v 2.2 board fidle circuit, but use a ztx689, ztx688, or tip120 transistor.

Instructions for the tip 120 can be found on www.megasquirt.info in the assembly section for the v3 board.

 

Where it says "PWM 2-Wire idle control", is this not the settings for the BAC? What does this control do, then?
The only difference from the FAQ that I can tell is the "Cranking (dc)" setting on the new firmware. I guess 50 (default) is okay?

Speaking of updates, why is there no MSQ file to download with the firmwware? Is that a bad idea?
We really could use some updated pics on the FAQ at least, I think. There have been some firmware updates and screen changes since the FAQ was written. The code is stable or frozen or whatever now isn't it?

edit: My bad, forgot about the note on the bottom of the FAQ. nm about the screen shot updates.

 

PWM 2 wire idle control is the BAC settings. 50 is fine for cranking DC, Just use whatever makes the car start up best without touching the gas pedal.

 

So for clarification, on a V3 board, you dont need the ztx689 or TIP120, you just hook the BAC up the same way you would for a PWM actuator (since it's two-wire)? Do you still need to route coolant to it? I got the motor without a lot of the emissions stuff connected, and the ACV is MIA. Is this needed, or can I just run a line to some point in the intake btwn the turbo and TB?
The BOV hard tube btwn the turbo and TMIC has also been replaced with one that only has a connection for a blitz BOV. So for a place to connect that line, i'm thinking of using the large nipple on the underside of the TMIC. Do you see any problems with this arrangement? Thanks!

Whew... acronym overload

 

you probably still need an upgraded transistor... most have also said that the v3 circuit does not work well for them in a PWM setup.

I usually just duplicate the 2.2 circuit with a ztx689 and a resistor between 400 and 500 ohms.

 

I don't run my bac, however, recently I was wondering if you could just have it run as on/off style air valve for fast idle in the mornings. (all I would use it for anyways) I was just wondering if you could do this on the standard 3.0 pcb kit hardware or would I have to run a better transistor or even a resistor in line. Because you can actually adjust how much air the bac intakes while open by turning the hex plug in or out.

dpf22

 

I still think it would draw too much current with the standard v3 board setup.

I don't know if just putting a resistor inline would work either...

The problem is that a lot of the megasquirt kit distributors replace the "standard" parts with pn2222a's. I'm not sure what the current limit on those is, but it's not very high... according to digikey it's 600 mA. This MIGHT do something with a resistor, but I'm not sure it'd open far enough to be of any help.

Ken

 

what about diy autotune, do they do the same, or do you know? I was looking at this seriously, however if I need to replace it to work, then I will. But I just am soo lazy after puting this thing together and I have a friend whome we are finishing a ca18det coil on plug ignition set-up via msns-e (still working out the fine details such as cas and wiring).
Thanx muy, you are the man, I ask a lot of questions lol.


dpf22

 

Would the BAC still need coolant routed to it?

 

the bac doesn't NEED coolant lines routed to it, but I still have them routed there... I believe it helps things on cold days..

All the megasquirts I've gotten from DIY use pn2222a's.

 

Can you suggest a place to pick up the ztx689 transistor?

dpf22

 

$1.21 at digikey.com

 

sweet thanx


dpf22

 

Sure, that should work just fine. I've set up mine to run that way, only powered via a toggle switch where the choke control used to be in my SA. A series resistor was added to limit current. I think I used a fuel pump resistor or the like. You'll need to really restrict airflow, as with the BAC fully open engine speed is pulled up far too high.

I've now added a TIP122 to control the BAC valve for proper closed loop idle control, but won't test until spring.

 

The coolant line for the BAC is to help prevent ice-up of the BAC in cold weather and to stablize operation.

 

Ok, well, it's easy enough to hook up, so i may as well do it. Is the BAC the same on a turbo and NA engine?

 

They are similar, likely identical electrically, but have differences in line routing and trim adjustment screws.