Subaru 3 wire IAC valve- how do I drive it?

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thomas1510
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Subaru 3 wire IAC valve- how do I drive it?

Post by thomas1510 »

This is the IAC valve on my ej205. Image

Anyone know what sort of valve it is? I'm measuring 710 ohms between one pair of pins, infinite resistance for all other combinations (EDIT: re-measured as 880 and 62k ohm between middle pin and each outer pin)- so I don't think it's the usual 3 wire pwm valve as described in the msx manuals.
Last edited by thomas1510 on Fri Dec 27, 2013 5:15 pm, edited 1 time in total.
98 Subaru Forester, ej205 turbo, MS2 extra.

1970 Datsun 510 turbo running MSx 029t. L20b with wasted spark, 4-1 crank wheel, td04 turbo
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by Matt Cramer »

My guess if you're getting infinite resistance between one pin and the other two is it's broken.
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thomas1510
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by thomas1510 »

Anyone know? It shouldn't be broken because my engine was running perfectly with the stock ecu before I megasquirted it. Here's a thread on nasioc.com where they discuss how to clean and overhaul the same valve http://forums.nasioc.com/forums/showthread.php?t=781242

I think I've found the correct factory wiring diagram for my engine. There is constant 12v on one pin, ground on another, and the third pin goes to the ecu.
98 Subaru Forester, ej205 turbo, MS2 extra.

1970 Datsun 510 turbo running MSx 029t. L20b with wasted spark, 4-1 crank wheel, td04 turbo
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by racingmini_mtl »

There might be internal diodes which would make it appear as if there is no connection but only if the probes are used one way. Try to make the measurements but invert the probes if you see an infinite resistance.

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thomas1510
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by thomas1510 »

Thanks for that suggestion racingmini_mtl, that may have been the mistake I made last night. Measuring again now it's about 62k and 880ohms between the middle pin and each of the outer pins. Still unsure how to work out its operation though. Power it up and try giving it some 5v pulses on the third wire?
98 Subaru Forester, ej205 turbo, MS2 extra.

1970 Datsun 510 turbo running MSx 029t. L20b with wasted spark, 4-1 crank wheel, td04 turbo
thomas1510
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by thomas1510 »

I've traced the factory wiring diagrams and it's definitely 12v, ground, and signal wire to the ECU. The ECU pinout diagram for this ECU pin (pin C10, red wire) gives this info: 0 or 13-14v, 'waveform'. I guess that's all I need to know to try it out with some 12v pulses :)
98 Subaru Forester, ej205 turbo, MS2 extra.

1970 Datsun 510 turbo running MSx 029t. L20b with wasted spark, 4-1 crank wheel, td04 turbo
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by emlclcy »

did you figure out how to drive the iac?
I'm in the same boat!
cheers
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by jmaz87 »

any update? I can't believe nobody has posted there settings for a WRX IAC
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by Matt Cramer »

You'll find MS3 settings for a 2002-2005 WRX IAC here: http://www.megasquirtpnp.com/downloads/ ... RX_134.msq
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by jmaz87 »

Matt Cramer wrote:You'll find MS3 settings for a 2002-2005 WRX IAC here: http://www.megasquirtpnp.com/downloads/ ... RX_134.msq
Thanks Matt but for the wiring is it just a normal 3-wire pwm? would i just use 2 med-current ouptuts and install a flyback clamp internally? I could use "IDLE" and "Fidle" and a 12v for last pin right

Image

Image
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by Matt Cramer »

Yep. It's your basic 3 wire PWM valve on these particular cars. Subaru's used a number of different valves, so these settings may not copy over to other cars.
Matt Cramer -1966 Dodge Dart slant six running on MS3X
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by tpsretard2 »

no you use one med current output, ground and 12v

will post more later for you and the settings.
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by jmaz87 »

Image

ya the stock wiring is definitely Ecu, 12v, Gnd which is why i got a little confused when it said 3-wire pwm IAC on MS3X used 2 med-current outputs after internally "clamping"

since nobody is disputing pin9 idle is getting used, ill leave that alone. what do they mean by pin 30 Fidle (mainboard) can be used if modified...
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by dontz125 »

jmaz87 wrote:ya the stock wiring is definitely Ecu, 12v, Gnd which is why i got a little confused when it said 3-wire pwm IAC on MS3X used 2 med-current outputs after internally "clamping"
Most 3-wire PWM valves are actually 2 coils back-to-back; 12v up the middle, and the 2 ends grounding via various driver arrangements. How much current goes through each coil determines where the pintle winds up. Idle (heh) speculation - I have to wonder if this isn't actually the same sort of thing with the drivers inside. Is the White / ECU wire carrying significant current, or just a logic signal?
what do they mean by pin 30 Fidle (mainboard) can be used if modified
The FIdle circuit on the V2.2 / V3.0 is too light to drive a PWM solenoid, and is only meant to handle a simple on/off valve. You can replace the original 2N2222 / 2N2304 transistors with bigger, heavier transistors capable of handling the juice. Take a look in the manual for more details.
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jmaz87
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by jmaz87 »

Thanks for the info but the question remains,
1) wire it like factory with IDLE, 12v, gnd
2) install the flyback clamp internally as per manual using IDLE, VVT, gnd
3) use same scheme from 1) with addition of a diode bridging 12v to IDLE
Which is supposedly the "external" mod (I saw somewhere)
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tpsretard2
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by tpsretard2 »

right sorry for delay, i was putting the head back on my EJ205, i bent a valve, the stock valve springs are crap.....But that is a different story.

The freq for the valve is 153HZ it is setup like a 2 wire valve. The body of the IAC has a driver in it. so tere is no need for a fly back clamp, there is a lot of cross info as the older ej20g/k/h/r engines has actual 3 wire iac's but swap to this setup for the ej205/255, ej207/257.

If there is anything else you need help with let me know..
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by jmaz87 »

Ok... if i do put the fly back clamp in will it affect the boost pin controlling a normal boost solenoid?
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by remsperso »

Here are the pins of my STI IAC valve :
Image

I have not the STI harness, and I don't know which pin correspond to the +12V supply, the ground and the PWM : could you tell me, please?
Thanks! :)
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Re: Subaru 3 wire IAC valve- how do I drive it?

Post by pierrox »

Unearthing this thread as I have a similar question.

A friend of mine got a Subaru EJ20E engine for his VW bus. It was installed in another VW bus and he bought the entire setup, down to the exhaust tailpipe. The engine runs with a Megasquirt 2, on a v3 pcb with a Zeal daughter board. Since the engine was installed for the previous guy, we don't have a lot of info on what was done, and as it's our first "real life" MS project, after weeks of reading theory, there are still a lot of things we're not familiar with.

We removed the engine ourselves, labelling everything so it could be reinstalled easily later. The engine was working when we did it. Once transplanted, at first the engine wouldn't work. Took a couple of trials and googling to realize the grounding of the ECU wasn't good enough, and that the camshaft/crankshaft sensor cables were picking up interferences from the spark plugs.

Now the engine is running as it did a few weeks back, when it was in the previous van. One big step. The previous owner showed us how idling is adjusted like an old school carburetor: a screw on the butterfly. It works but it's definitely not in line with the rest of the machine! I noticed that the original Subaru IACV is still in place, but it was unplugged There's also an old handwritten label "Idle not connected" on a cable going to the ECU. So I assume there was an attempt to have it connected. I tried to connect it but it didn't change anything.

As I wrote first, the MS has an extra daughter board, a Zealboard. From what I understand, that's a mod that was done to accommodate for the second necessary VR sensor - the engine stock ignition has the 6/7 trigger system. But then from I read, this daughter board also adds a PWM IAC driver. And it looks like there was at least an attempt to have it working:

Image

But upon inspection, the IDLIN wire is not going anywhere:

Image

According to the board assembly page, it should go to Bottom end of R19.
I'll need to test all the wiring that's going to the IACV to see exactly what was done. For those of you with experience in the Subaru field, how should it be wired to work? So that I know what I should find when examining the wiring.

Thanks!

Side question: I've been looking for stock (or stock-ish) ignition tables and AFR tables to compare with what the MS ECU is doing, can't find any. Where could I find this info?
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