bypass air control solonoid

[JasonGrahn]

Can anyone with an automatic confirm that their air control solonoid has 3 pins on ths solonoid itself? the '92 service manual says it does, but my manual-transmission equipped model appears to only have 2 pins.

I need to figure out a way to get the three-pin solonoid from the 2.5L engine to behave the way the 2-pin solonoid does from my 2.2L. This is the last roadblock in the engine swap.

[vrg3]

90-91 5MT non-turbos have different IAC valves from all other BC/BFs. I didn't know they only had 2 pins, but another difference is the size of the inlet; your stock valve's inlet was 15mm rather than 19mm like most.

The 3-wire valves actually have two solenoids in them. At rest the valve is partially open, and the ECU can actuate one solenoid to open it or the other to close it. I guess the 2-wire valve only has one of these?

Is the IAC valve on your EJ25 manifold the type that's mounted in the same place as on your EJ22, or is it attached to the throttle body? If it's the latter, you might find that a BC/BF ECU simply can't properly control the valve; I'm not sure about that.

The simplest solution to your problem might just be to swap in an ECU from a 92-94 car.

[JasonGrahn]

90-91 5MT non-turbos have different IAC valves from all other BC/BFs. I didn't know they only had 2 pins, but another difference is the size of the inlet; your stock valve's inlet was 15mm rather than 19mm like most.

The weird thing is my factory engine wiring harness has 3 wires running to the IAC. I was informed that the automatics have 3 wire IACs, but have no difinitive answer to this.

The 3-wire valves actually have two solenoids in them. At rest the valve is partially open, and the ECU can actuate one solenoid to open it or the other to close it. I guess the 2-wire valve only has one of these?

Sounds like it. I'm guessing the 2-wire is a basic ON/OFF switch for the IAC. Any idea HOW the 3-wire operates - which wire controls what?

Is the IAC valve on your EJ25 manifold the type that's mounted in the same place as on your EJ22

Yes.

The simplest solution to your problem might just be to swap in an ECU from a 92-94 car.

Hoping to not have to do this.

[Legacy777]

The MT IAC valves on the 90-91's used a recipricating valve, vs. the others which was a rotary valve.

I think you may need a different ECU. Looking at the wiring diagram for the IAC valve. The ECU for the MT cars supplies a voltage on pin 2 and sinks it on pin 1 for the IAC valve. On the AT cars, both pins sink voltage, and the third is connected to a 12v source through the ignition relay.

You could try messing around with the MT/AT identifier pin on the ECU.......

We know that turbo cars have the same ECU regardless of MT/AT. However non-turbo cars have different ECU's.......and I will probably run into some issues this summer when I do my swap with the ECU issue. I might be able to mess around with the MT/AT identifier......that might not work, and I'd need to find an ECU from a 92-94 n/a car.

That may be the option you'll have to go as well......

[Legacy777]

The weird thing is my factory engine wiring harness has 3 wires running to the IAC. I was informed that the automatics have 3 wire IACs, but have no difinitive answer to this.

This is true...can tell you this with 100% confidence. They aren't going to have a separate wiring harness for the MT cars.

Sounds like it. I'm guessing the 2-wire is a basic ON/OFF switch for the IAC. Any idea HOW the 3-wire operates - which wire controls what?

See my post above. The ECU modulates when it sinks current to adjust the duty cycle on either side, which opens & closes valve.

Hoping to not have to do this.

Unfortunately....I think it may be the case as well.....

[vrg3]

The weird thing is my factory engine wiring harness has 3 wires running to the IAC. I was informed that the automatics have 3 wire IACs, but have no difinitive answer to this.

The automatics do have 3-wire IAC valves. All non-turbos except for 90-91 5-speeds have the same type of valve.

What color wires actually reach the valve?

Sounds like it. I'm guessing the 2-wire is a basic ON/OFF switch for the IAC. Any idea HOW the 3-wire operates - which wire controls what?

The yellow/red wire in the middle of the connector carries +12v. When the ECU grounds the black wire, it closes the valve. When the ECU grounds the white wire, it opens the valve.

Let's pretend for a second that your stock ECU can signal the valve to open and that it's normally closed. You could maybe connect the stock wire to the white wire and invert the signal for the black wire. Inverting the signal would be pretty simple; the signal from the "open" side could go through a resistor to the base of an NPN darlington transistor.

The only concern I'd have about doing that would be the potential for overheating the solenoid coils. It's possible that the coils were designed only to be pulse-width modulated and not to be powered continuously. If that's the case, and if your ECU tries to leave the valve closed, you might overheat the coil. That's a lot of ifs, and this is hypothetical at the moment anyway, but... those are my thoughts.

The simplest solution to your problem might just be to swap in an ECU from a 92-94 car.

Hoping to not have to do this.

Why? It would only take a couple minutes.

Wait a minute -- couldn't you swap your stock EJ22 IAC valve onto the EJ25 manifold? You might have to get a little creative with some gasket paper and/or weld on or drill a bracket or something, but then you'd know the valve and ECU would work together.

By the way, which fuel injectors are you running? I'd imagine you'd need injectors of the same capacity as stock for the ECU to manage them right.

[JasonGrahn]

The MT IAC valves on the 90-91's used a recipricating valve, vs. the others which was a rotary valve.

So like up/down versus spins side to side?

The ECU for the MT cars supplies a voltage on pin 2 and sinks it on pin 1 for the IAC valve.

So the 2pin is a constant power with a ground switch?

On the AT cars, both pins sink voltage, and the third is connected to a 12v source through the ignition relay.

whereas the 3 pin has a constant power with two switched grounds?

You could try messing around with the MT/AT identifier pin on the ECU..

I am not aware of this pin. Would i be basically tricking the car into thinking its an auto to fix the idle issue, then tricking the car again into thinking it's a manual to solve the issues dave encountered here: http://legacycentral.org/library/transm ... ronics.htm ??

[vrg3]

In 1992 all Legacies had the same ECU.

Jason, if you're willing to try a different ECU I believe I have one from a 1992 that I could sell you pretty cheap.

[JasonGrahn]

I stewed over it a bit tonight. I'm going to try the old school method --> adapter plate. without swapping ECUs (and worrying about any potential headaches that will cause), this looks to be the only course of action to use my OEM 2.2L bypass valve with the stock wiring etc, etc... We'll see how it goes!

[vrg3]

Cool.

So the stock EJ22 valve doesn't have the same type of mounting flange as the EJ25's?

The only headache I can imagine the ECU swap causing is also having to swap the MAF sensor to the plastic-body one.

[Legacy777]

Let us know how it goes Jason......

Like vrg3 mentioned....the only real headache I can see from swapping ecu's is MAF.

vrg3.....that's good to know that the 1992 MY all the ECU's were the same.