This may not concern many people as few probably use the BAC valve anymore.

I do though, I also use the thermowax. My goal is drive-ability, and stable warm ups/idling.

Anyway, we see a lot of base maps and some have BAC settings. Now you have to play with the min and opening values as each engine is different. The point here is all these base maps have that 33ms pulse width. This is wrong obviously. If stock is quiet, and this sounds like a jack hammer, we are all doing it wrong.

I used my google and looked up "bac valve frequency" or something of that nature. I found some interesting info. BAC valves operate 300-100Hz frequency. I found a random RX7 page that says our BAC operates at 125Hz. That means 125 times per second. 1000ms = 1 second. So 1000ms divided by 125 times = 8ms

What the hell is 33ms for then?!

I set mine to 8ms and switched my key to ON. I couldn't even hear it! I had to double check by plugging in a spare BAC and keeping it near by. Just a low "HMMMMMMMM".

So if you've given up on the BAC, maybe it's time for another try. I hope we all learned something here.

PS
the haltech manual (i have e6k) even says the valves typically are around 10ms

 

The FD BAC/ISC valve operates at 244hz according to the service highlights document:



In my experience it functions identically to the FC BAC valve, electrically speaking. Using your calculation that would mean about 4 msec. So you could try that as well.

 

AHHHH FUUUUUU

What page is this on?

well, like I said I stumbled upon a website that said 125Hz. i also googled and found 300-100Hz so I went from that.

 

It was basically in the same place that idle control stuff is in every Mazda service type of document. page F-45 in the service highlights document available in the 3rd gen section sticky thread. Read the table of contents for fuel and emissions control.

 

woops, I forgot to mention I gave an FC. Maybe 244Hz still applies.

 

it does, the FC books mention the 244hz too.

are you sure you can use the thermowax? i remember on the E11/20B the thermowax didn't work because it opens the throttle, so the TPS doesn't read zero. the e11 wanted to see 0 throttle to turn the BAC on

 

You can use the thermowax and BAC by setting the throttle pump dead band. I use 2%. The dead band is there to "ignore" the first 2% throttle applied.

It works well because I need the BAC around 75+ degrees when the thermowax is fully open, but the car isn't still quite warm enough so it idles a bit low. Any cooler and the thermowax does the job without aid from the BAC.

I'm still playing with the opening and minimum positions but now I'm liking the non-jack-hammer noise.

 

If you're using the BAC and have it working properly, the thermowax is entirely redundant. BAC will control cold start idle up by itself without the need for assistance from the thermowax.

 

^That is true. I actually had my car idle up with the BAC a while back. I managed to make it work using the crappy 33ms setting. Sometimes though, my BAC doesn't work. It takes a few seconds before it wakes up. I've tried different ones too, I think the e6k is on the fritz. No harm in using the thermowax. Why did mazda use both? Maybe in case the BAC froze in cold environments?

 

Ignition timing and emissions are limitations. Mazda has to run retarded ignition timing at idle and during warmup in order to keep the catalytic converter warm. That certainly doesn't help idle stability. The BAC valve has a coolant hose to keep it from freezing up. Modern electronic throttlebodies have the same thing.

Mazda isn't the only manufacturer to use mechanical idle system in addition to a separate idle air control valve. For example the Mitsu engines of that era (4G63, 6G72) have a fast idle valve that is controlled by coolant flow. It's an actual separate pintle valve that moves based on coolant temperature, as opposed to having a system that moves the throttle plates like Mazda uses.

 

I've played with the BAC timing some. Right around 11ms is where it starts to get noisy. At 10ms, it is hard to hear. At 11ms, it is audible and the higher you go, the louder it gets. From what I have seen with my e6k and s4 bac, the BAC responds and holds idle much better with a higher ms number. I used 21ms for many months, before becoming annoyed at the noise.

Around what numbers do you guys run for your cold & hot min & opening positions? I was running 30-45s at 19ms.

 

where do you set the ms? I have my BAC frequency set to 225hz and mine is quite. I will try it on 244hz and see how it does.

 

ms is the old E6K/X terminology. Hz is used in all the newer stuff. You will see no difference between 225 and 244 Hz.

 

Right. I've got the antique e6k which requires ms and not Hz. I have used the newer Haltech plantinums that those let you spec the bac in Hz.

 

Is Hz used on the E11? I currently have my 20b idling with the BAC and it does buzz pretty loud on start-up or whenever it controls high idle.


Edit: Damn why ask a dumb question when I can just hook up the laptop and see. LOL! I never changed the Hz setting and it's currently a 50Hz. So I basically need to change that setting to 244Hz and re-adjust my idle settings?

 

Mine is weird... at 8ms it worked, but at 4ms it didn't. The I tried another BAC and the opposite worked!

My minimum positions are also weird. 80 cold and 80 hot. if i do 79 cold, my idle drops like a blind roofer. If I do 81 cold, it shoots up too high and starts surging. I put my minimum positions to 10 for both.

My car will start fine cold or hot without the BAC, I just want it for an idle bump in the 75-130 degree ranges.

 

Yep.

 

1ms equals 1khz. So, take the common frequencies used by the factory of somewhere between 240 and 300 and divide by 10. That gives you the ms you should use. So you need to bump the cycle up to 24-30. Think Haltech actually calls for 33. At any rate, bump the cycle time up and I think you'll get much more consistent results.

 

^eeerrrr, negative. 244Hz is 244 times per second. I have 1000ms in 1 second. I want to use my pulse 244 times in that second. 1000 / X = 244

Solve for X

The haltech manual even says a BAC typically operates around 10ms

33 is obviously not right as it sounds like a jack hammer and stock does not.

Edit:
check this calculator
http://www.sengpielaudio.com/calculator-period.htm

 

Eh, you're right. It didn't even sound right when I was typing it. Must have been the beer talking.

 

Did some recent adjustments and it's much more quiet now. All I hear is a hiss! Now I have to fix my intake leak I just found.

 

Does anyone know what the stock computer uses as far as positions and openings? So far all we know is the frequency. I keep screwing with the damn thing. I should just leave it alone...

 

^I'm having a hard time as well. I had this engine idling down perfectly a couple days ago after adjusting the Hz to 244. Every since I fixed my intake leak, I'm having a hell of a time re-adjusting the %'s. I know for a fact that I have zero leaks now. This is weird! Before when I had the HZ setting defaulted to 50HZ, it was noisy but whatever % I put in to control idle, the BAC valve responded accordingly. This doesn't happen when I changed the setting to 244HZ. It doesn't seem to wanna do anything till I put something 50% or higher. After reading the manual again, I believe I need to adjust those PID setting to properly sync everything up again. Does anyone not know what Proprotional and Integral Coefficent settings their using for the Fd BAC valve?

 

P - 20
I - 10
D - 0

Should get you in the ballpark. The most important thing is to get the start duty as close as possible to what holds a steady idle. Monitor the duty output on that channel and set the start duty accordingly.

 

Thx for these numbers. I will plug those in tomorrow and try again. Could you rephrase your explanation here on monitoring the duty output? Originally with the default 50HZ setting, I could adjust the minimum duty and the BAC would raise or lower my idle accordingly. At 244 HZ this doesn't happen at all. It's almost like the minimum duty doesn't work anymore. So your saying I have to put more focus on the start duty now as opposed to the minimum duty?