custom13B

I'm hoping someone can respond with a way to control the BAC idle valve with a V3 board. I read all the FAQ's here and on the MS forum as well. I have a ZTX 688 transistor from digikey as Muy suggested in the FAQ. My question is which way to install it. One side is labeled ZTX688 and is contoured slightly differently it is no bigger than the stock transistor. Besides soldering that to the board which wires from the DB connector go to the BAC valve? Any help would be greatly appreciated.

muythaibxr

the fidle wire goes to the bac valve... and there's a +12v wire that goes to the BAC as well...

From what I've been told, you basically have to duplicate the v2.2 modded circuit to control the BAC valve.

1) First, remove Q20 and R39. Replace Just jumper R39 instead.
2) Replace R19 with a 510 ohm resistor.
3) Replace Q4 with a ztx688 (orient it with the flatter side the same direction as the flat spot on the silk screen) Leave a little bit of space under the ztx688 when you solder it.
4) remove D8
5) Using a 1N4001 Diode, jumper pin 3 of the ztx688 to a +12v source. The banded end of the diode goes to the +12v source.

That's it, just run the wire from the fidle pin on the db37 to one of the pins on the BAC valve, and make sure the other pin on the BAC valve has a +12v power source.

The instructions above basically duplicate the V2.2 circuit with the ztx688 in it. At one point or another, I'll try to do it with less mods, but there is a person on the megasquirt forums who tried it several ways, and destroyed several ztx688's to come to the conclusion that duplicating the v2.2 circuit but using a 510 ohm resistor instead of a 1k resistor for R19 works the best.

Eagle7

Thanks, custom13B. You beat me to the question by a couple hours. And many thanks to Muy. You have been incredibly helpful.

custom13B

Muy has been a great help. And that reminds me Muy if you still want those N326 ecu's I'll give em to you and tofuball for 20.00 each since I never could have done any of this without your help. Any cheaper than that and I'll use em for a boat anchor. Let me knoe and thanks once again. Shawn

custom13B

One last question how do I know where pin 3 is on the ZTX688? The pin orentation isnt shown on the MS schematics. Do you count from left to right starting at 1 on the labeled side?

muythaibxr

with the flat side facing you, from left to right it's 1,2,3

or

Emitter, Base, Collector.

djs2571

The ZTX 690 would be a better choice for Q4, the 688 is only a 12V part, and will likely die due to overvoltage. R19 shouldn't have to be replaced either, these parts should have enough gain to work properly. Though I don't have a car in front of me to verify if this should be changed too.

Q20 and R39 make up a current limit circuit, which should be left in place if possible. The 1 ohm R39 in there it's about 500 - 550mA limit, dropping a second 1 ohm in parallel with R39 to get 1/2 ohm should get the current up to a good level for the BAC valve operation.
http://www.megasquirt.info/ms2/pcb.htm - D8 shouldn't be removed, though it may be replaced with a 1N4004 diode (4001, 2, 3, 4 works fine) though the line should go to ground side instead. Or just place the diode across the coil, which is basically what is stated below.

djs2571

to clarify the wording on D8.... the orientation for the part they show in there is correct, if a normal diode is used it should be reversed from that. What is in there is a zener, and it's drawn correctly

djs2571

ok, it's just too late now that i'm reading this again. IF D8 is replaced with 1N4004 it should also have the line pointing to battery.
If anyone wonders the current in a normal diode will flow towards the striped end being negative, in which case you'd end up with the valve on all the time. To protect the driver to a coil against the inductive kickback a diode should be placed across the coil with the line on the positive side.

i'll try to stop confusing people now.

Dave

muythaibxr

Several people have confirmed that if they use the standard v3 circuit, and only replace Q4, that transistor will fry on a regular basis. The ONLY way that I've seen it work right is to completely redo the circuit to look exactly like the 2.2 circuit.

Also, I've never seen a problem with using a ztx688, but I'll keep in mind that it's a +12v part. Also, the ztx690 is only rated for 2A continuous, which may not be enough...

I've never tried what you describe... Here is where I got my info that dupicating the v2.2 circuit was the best:

http://www.msefi.com/viewtopic.php?t...ghlight=ztx688

He apparently never tried replacing just R19 and Q4, so I'll try that as soon as I restock on ztx688's...

However, the instructions I gave will definitely work according to RyanPzz on msefi.com, and have worked in several installs in v2.2 boards.

custom13B

Muy I was talking to Djs about this earlier. Thanks for your input btw. He's being nice trying not to step on anyones toes..he's a electricial engineer a damn good one I personally know. If he says somethng will work it will. I am trying your method and his. I am trying yours first as I already have the parts in hand and desoldered the stock parts already. I am going to order a ztx690 and some resistors if his version is more reliable great I hate broken cars in the summer waether. I will let you know how things go. Thanks again to everyone for thier input.

muythaibxr

I'd recommend the ztx689 if you're going to go with something other than the 688... although several people have tens of thousands of miles on their installs with ztx688's....

the 689 has a higher current rating than the 690, and a higher voltage rating than the 688.

I'm just going from what has been proven to work in many v2.2 installs (including tofuball's).

Eagle7

Which pin on the S4 harness does this connect to?
And while we're talking about pins, which one do I use for +12V - looks like 3I to me.

Thanks,

muythaibxr

the one all the way upper right of the connector if you're looking at it from the back of the connector is +12v...

I'd have to look at the FSM again to find out which pin is for the BAC valve.

Eagle7

Yup, 3I.
Thanks.

muythaibxr

wait, I meant upper left... it's upper right with the connector pins facing you... upper left if you're looking at it from the wire side... That's on the 10 pin connector.

Eagle7

Looking from inside the ECU, upper right would be 3I, which the FSM has connecting to the high side of most of the solenoids and comes from the main relay.
Upper left would be 3A, which the FSM has going to ground, along with 3G and 2R.

My other question was whether the idle control goes to BAC (pin 2Q) or Air By-Pass Relay (pin C). My guess is BAC. What's the difference between them? From the FSM diagrams, they both seem to feed snorkel air into the intake past the butterfly. And what's the purpose of the water hose on the BAC?

Thanks,

muythaibxr

hrmm, OK, well the manual lists the pins as if you were looking at them from the wire side of the connector. I believe they do it this way so it's easier to back-probe the connectors to check voltages and such....

With the ztx688/689/690 (whichever) you want to hook up to the BAC valve.... If one is a relay and the other is the BAC valve itself, then the difference is that the BAC valve is a 2 wire PWM controlled valve... meaning it can be partially open...

If the other one is a relay, it's either on or off... with no control of how open it is...

I'm not sure what purpose the water hose on the BAC serves, except maybe to keep it from freezing when it's cold outside.

Eagle7

Do you happen to know the configuration of the S5 intake, and how it does idle control? I've got an S5 intake with an S4 harness. I just checked my car and I don't have a BAC installed and don't see that there's any place to put such a device. There is an Air Bypass Valve installed (don't think it ever did anything, though).

Looking through the Mazda parts catalog, it looks like the S5 does have the same BAC valve, but I can't tell where/how it mounts. A quick look at my S5 intake I didn't see any mounting spot.

Eagle7

The best I can figure out from the picture in the parts catalog, the S5 BAC must mount somewhere under the throttle body. I'll have to take it apart and see what I find.

muythaibxr

it's on the upper intake manifold below the throttle body I believe...

rotarygod

iTrader: (1)

Ken,

I have a V2.2 board. All the info I can find is telling me how to mod a V3.0 board to make the BAC valve work. Apparently I'm not searching hard enough or I don't know what I'm looking at because I can't tell what the instructions are to make it work on my board. I probably am just blind though. Can you give me a link that shows me what to do on my board?

muythaibxr

for the v2.2 board the info is in the FAQ:

"If you plan on controlling your BAC valve on a v2.2 board, you'll want to get a ztx688 transistor, and replace Q5 with it. Also, you'll want to get a 1/2 watt 510 ohm resistor, and replace R16 with it."

Not trying to be smart... just showing you

rotarygod

iTrader: (1)

I told you I was blind!

PM me your address so I can send you this S5 ecu. I can't find my old S4 ecu though.

How's the RX-8 code coming along?

muythaibxr

I gave the rx8 code to jsmcortina on the msefi list to look over it, but he hasn't had a chance... I've got some code that I think SHOULD work... but I'm not positive.... after he looks it over, I'll make it available as I still haven't bought the rx8 vr sensor, so I think the only way to test is going to be to disconnect your coils on the rx8, and make sure you get rpms when cranking... I'll ping jsmcortina on it when I get a chance.