Benchtest IABs-How to?

[H.M.]

I have a F22A6 IAB/Butterfly and black box sitting on my bench. Trying to test it before I put it in my car.

If I apply suction to the diaphragm the butterflies close. That's good, right?
If I apply suction to the end of the #12 tube where it attached to the IM, I get a vacuum that holds. So that's good, right?
If I apply 12v to the electrical connection the vacuum is released from the black box. So that's good, right?

Here's the part that's confusing me.

If I apply suction at the #12 tube as above, shouldn't that suction travel into the black box, create a vacuum there that also creates suction at the diaphragm and holds the butterflies closed?

It doesn't do that so I'm wondering what creates the suction to keep the butterflies closed.

I'm thinking that the solenoid should be allowing that IM suction to pass through it to the diaphragm and it's not. Is that correct?

[cloudasc]

The engine generates the vacuum that pulls the iab solenoid closed. When the ecu activates the iabs it grounds the wire, which releases the vacuum, causing the iabs to open (cause they are spring loaded).

The black box doesn't suck or create vacuum on its own, that's the engines job. As you rev the engine you lose vacuum pressure. The black box is essentially a reserve of low pressure (vacuum) during high revs when the engine isn't generating enough vacuum to hold the iabs closed on their own.

[H.M.]

Got it. I understand that part.

But if I use a vacuum tester to create vacuum it pulls the iab solenoid closed if I hook it up directly to the solenoid.

If I hook up the vacuum tester to the hose leading into the black box, the box holds vacuum BUT the vacuum doesn't pull the iab solenoid closed.

Shouldn't it?

[H.M.]

C'mon....I know one of you has an opinion on this. Consider it a thinking exercise.

If the solenoid is closed until current is applied at high RPMs, how does the vacuum, which originates in the IM and travels into the Black Box where it is held by the closed solenoid, suck on IAB diaphragm at low RPMs?

If we solve this I have another one that involves two CB7s:
Both drivers leave a destination at the same time traveling in opposite directions at 5mph over the speed limit. One has a stock 93 DX with new timing belt, engine seals and suspension bushings. The other has a slammed 93 EX with custom paint, 3 inch exhaust and side rears obscured by stickers. Which driver gets laid first?

[cloudasc]

For you to get vacuum through the black box, the solenoid would have to be activated/opened at least once, to set the vacuum? Then when the valve closes, it keeps the vacuum in the hose between diaphram and the valve?

[H.M.]

Ok, that sounds logical.

So maybe the ECU opens the solenoid for a moment to set the vacuum on the diaphragm (and close the butterflies). Then closes the solenoid to hold the vacuum everywhere until it again opens at high RPM to de-activate the diaphragm (opening the butterflies).

Then the whole cycle starts over...


Is that how the ECU works?

[cloudasc]

Is that how the ECU works?

Hook up a test light between the iab pin (a17?) and a power source, and see if the light turns on at all while or after starting the car. Either that or you could try and watch the diaphram.

IAB's have two set points in the ecu if I am correct. One is the rpm at which they activate at, and the other is when they deactivate. The rpm they deactivate at is much lower (4200rpm range?) then the rpm they activate at (4800rpm?). By the time the rpms get back down to the deactivation point, I believe the engine might be already making enough vacuum to pull the diaphram closed, then the ecu signals, and it closes the valve holding that vacuum, until the next time its needed. So the ecu technically would only have to briefly activate once, most likely during startup to set the vacuum.

[H.M.]

Ok, thanks and that makes sense to me.

I was actually trying to test the black box, solenoid, diaphragm before I installed it and though they all "worked" it didn't make sense how they functioned together.

If I assume the ECU operates as you describe, it makes sense.