Bosch 3 wire PWM idle valve questions

[heychris_1]

All,

I'm inches from my first start on my MS3x converted BMW 2002.

I've got a couple of questions on PWM idle valves.

1. The documentation state "Normal, 0%=off - This means that 0% duty turns off the idle valve."
Does idle valve off mean that it doesn't allow any air to flow through? (just want to make sure I fully understand)

2. I am using the bosch 3 wire idle valve from an 1990 e30 BMW 325i. Searching the forum sounds like 60-120mhz will work for it. I first tried 76mhz. In test mode I'm able to fully open and fully close the valve. Also 50% appears to be 50%
Trying 25% and 75% also result in fully closed or open. I've tried different pwm frequencies, but that seems to have made it worse, even when I switch back to 76mhz.

I'm an engineer and understand how PWM works, but not sure how it translates to this valve.

Is it possible the valve is just bad?

Can anyone recommend a valve testing procedure?

Thanks!

Chris

[jsmcortina]

MSQ ?
Have you enabled 3 wire mode? How do you have it wired? I tested a 3 wire valve on the bench after I added that feature.

James

[sjf911]

I have a brand new Bosch 3-wire on the Porsche that is functionally completely closed at 35% and functionally completely open at 70% so your results look pretty typical to my small series.

[VolvoGuy50]

I had a hard time getting the 3-wire one to work on my S70. I wound up just ditching the IAC entirely until I can bench test it further and figure out how to properly control it.

[gurov]

i have a 3 wire valve on my sentra, running in 3 wire mode, and it works fairly well, make sure you're driving it from the ms3x board entirely, not idle and f-idle, so you're using the same transistors for both coils.

[VolvoGuy50]

The way the Bosch valves work is 1 pin is +12V, and the other 2 wires are effectively grounds. Grounding one causes the motor to open, grounding the other causes it to close.

[muythaibxr]

+1 gurov.

I'm also using a 3-wire denso valve on the corolla, and it works fine as long as you do what gurov says.

Ken

[VolvoGuy50]

+1 gurov.

I'm also using a 3-wire denso valve on the corolla, and it works fine as long as you do what gurov says.

Ken

Can this be done on the Bosch valves? I was trying to drive mine using F-Idle and MS3X Idle, but that's only because I assumed they require opposing signals. I have seen people just tie the "closing signal" wire to ground and run it as a 2 wire valve before. That seems to work well from what I've read. I'll try and bench test it once I fix my DC supply...

[nuvolarossa]

i have a 3 wire valve on my sentra, running in 3 wire mode, and it works fairly well, make sure you're driving it from the ms3x board entirely, not idle and f-idle, so you're using the same transistors for both coils.

I have a bosch 3 wire on my bimmer driven from idle and f-idle and running pwm closed loop. I tried it on bench before and it worked great. Obliviously it works great in car too.

Which kind of troubles may give driving it from Idle|f-idle?

[jsmcortina]

I wrote the 3 wire mode so the 3-wire valve can be driven as the manufacturer intended.

Using FIDLE and Idle will certainly be ok with the V3.57 mainboard as it uses the same driver as the MS3X. It ought to work with a modded V3.0 too, but the point gurov makes is fair - using identical drivers for both sides is good practice.

James

[hassmaschine]

I've bench tested this exact valve (E30 3-wire PWM) and got pretty much exactly the same values 75% open, 20%-something closed. The closed value was actually more vague than the open value, which was obvious. It seemed to continue moving up to about 10% but it was hard to see by eye. as far as the frequency I think I'm running mine at 90hz or whatever the closest to that is that you can select.

and I'd definitely be running it off the MS3x, with an M20 you aren't going to need all those PWM outputs for other things like VVT anyway.

[elaw]

I have seen people just tie the "closing signal" wire to ground and run it as a 2 wire valve before. That seems to work well from what I've read. I'll try and bench test it once I fix my DC supply...

That sounds to me like a recipe for a fried valve!

Think of a 3-wire valve this way: it's essentially two motors, each trying to turn the valve in the opposite direction. Grounding one of the signal wires basically means you're running one motor at full power all the time and PWMing the other, and letting them fight it out for where the valve ends up.

If you wire it the right way, you never have a condition where both "motors" are fighting each other.

[gurov]

I have seen people just tie the "closing signal" wire to ground and run it as a 2 wire valve before. That seems to work well from what I've read. I'll try and bench test it once I fix my DC supply...

That sounds to me like a recipe for a fried valve!

Think of a 3-wire valve this way: it's essentially two motors, each trying to turn the valve in the opposite direction. Grounding one of the signal wires basically means you're running one motor at full power all the time and PWMing the other, and letting them fight it out for where the valve ends up.

If you wire it the right way, you never have a condition where both "motors" are fighting each other.

this is how the manual recommends it done for ms2 that is without a 3 wire mode.

[jsmcortina]

Well yes, but why mess around with that when we've provided a true 3 wire implementation !

James

[heychris_1]

My 3 wire bosch valve is being run purely by the ms3x using idle and vvt.

Is there a procedure for finding the right frequency?

[elaw]

I think the scheme in the MS2 docs is a bit like I described above, but you're running one of the "motors" at partial power all the time instead of full power. It's far from ideal, but better than nothing if you only have 1 driver available.

Re finding the best frequency, I'd say use trial-and-error to find the highest frequency where the valve operates properly. If you select too low of a frequency, the valve will be constantly moving back-and-forth which I'd expect to cause a lot of wear.

[red-racing]

How do I setup this valve in MS2?
3-wire mode

[grom_e30]

i don't think ms2 can do the 3wire, so would be either the big resistor or a circuit to drive both coils

[piledriver]

My 3 wire bosch valve is being run purely by the ms3x using idle and vvt.

Is there a procedure for finding the right frequency?

99 hz is the frequency VW uses.

Using one off a Vanagon using idle and VVT off the MS3x, works flawlessly.

Center tap is 12v.

You can do it on MS2 if you add a n additional driver and pull an inverted signal off fidle so you have complementary outputs..
Of course I was doing it through an MS3X, via an MS2Xt adapter, which is entirely like cheating.
(Dontz125s idea)

[prof315]

I'm also using a 3 wire Bosch from a CIS-E VW Golf at ~100Hz using the MS3X Idle and NO2-1 outputs on a customer's race car. It works well enough that even with a 308* cam, the engine starts and idles at 1300 rpms cold, hot or anywhere in between with no throttle assist.