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Discussion Starter · #1 ·
Howdy folks!
The DISA valve has a couple of things that look like vacuum pots, but I don't see a hose to go to it. Does it get vacuum from somewhere else, and is the hole in one of the pots just a bleed hole to let air in or out? :rolleyes:
 

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No hoses go to the DISA, only the electrical connection on top. Those are indeed vacuum holes I believe, but nothing you have to do to it. They just come in handy when trying to test if your DISA still works.
 

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Living Life At The Beach
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Thanks moiz!
One other question: One of the front turn signals has a bunch of moisture in it for some reason. Anyone else seen this problem or know of an easy fix?
Probably just some moisture from driving through a puddle at just the right angle ect. You can try what works for my on my MDX. Use a hair dryer set to medium to dry it out. Just point it at the lens. Don't let it get too hot though. Keep the nozzle moving and try to avoid the paint. If that doesn't work, you may have to remove it, take the bulb out, and retry.
 

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Seek to understand,^Value
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Does it get vacuum from somewhere else, and is the hole in one of the pots just a bleed hole to let air in or out?
You asked THE MILLION DOLLAR QUESTION!

Some of us have been trying to figure out the DISA vacuum operation for a month now (disassembling old DISAs is the best way).

PLEASE (pretty please) add value to the canonical thread below:
- How the DISA valve operates (0)

Note: I culled that thread out of this bestlinks list:
- How the DISA valve operates (0) (1) (2) (3) (4) & how to test DISA operation (0) (1) (2) (3) (4) & a simple DIY to install an M54 DISA (1) & a nice DISA autopsy (1) (2) & a great DISA group buy (1) & how the disa valve o-ring fails (1) (2) & how it can reputedly cause all sorts of cold-engine rough idle problems (1) (2) & where to get just the DISA valve o-ring (1) & why you want to check the DISA at 100K miles or whenever the airbox is removed (1) (2) & how some 'repair' a rattling DISA unit (1) (2) (3) & why the DIfferenzierte SAuganlage ("Differential Air Intake") valve flap breaks (1), sometimes with parts sucked into the intake manifold (1) (2) (3) (4) (5) (6) (7) (8) & a well documented example of how a broken DISA flap can ruin your engine (1) & yet another seemingly complex set of misfire codes reputedly traced to a broken DISA valve (1)


 

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Seek to understand,^Value
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Those are indeed vacuum holes I believe, but nothing you have to do to it. They just come in handy when trying to test if your DISA still works.
I don't profess to actually 'understand' how the DISA vacuum assist works (particularly how it lets go) ... but ... from what I've read ... the two vacuum ports 'do' do something.

I'm particularly perplexed as to how the vacuum assist (which seems to be stored inside the DISA itself), is regulated to 'let go' when the 13.8 volts is removed from the electrical solenoid.

See just one (still incomplete) explanation below from the thread I referenced prior:

The resonance system provides increased engine torque at low RPM, as well as additional power at high RPM. Both of these features are obtained by using a resonance flap (in the intake manifold) controlled by the ECM.

During the low to mid range rpm, the resonance flap is closed (i.e., the flap is actuated by alternator voltage such that it is held vertically against spring tension). This produces a long/single intake tube for velocity, which increases engine torque.

During mid range to high rpm, the resonance flap is open (i.e, the control voltage is reduced to zero which causes the flap to return to the horizontal rest position due to spring tension) . This allows the intake air to pull through both resonance tubes, providing the air volume necessary for additional power at the upper RPM range.

When the flap is closed, this creates another "dynamic" effect. For example, as the intake air is flowing into cylinder #1, the intake valves will close. This creates a "roadblock" for the in rushing air. The air flow will stop and expand back (resonance wave back pulse) with the in rushing air to cylinder #5. The resonance "wave", along with the intake velocity, enhances cylinder filling.

The ECM controls a (magnetic) solenoid valve for resonance flap activation. At speeds below 3750 RPM, the solenoid valve is energized (with alternator voltage at the harness connector) and vacuum supplied from an accumulator closes the resonance flap (where the vacuum accumulator is apparently a one-way flap valve with a 1/16" entrance hole in the side of the DISA) . This channels the intake air through one resonance tube, but increases the intake velocity.

When the engine speed is greater than 4100 RPM (which varies slightly - temperature influenced), the solenoid is de-energized (i.e., the harness control signal goes from ~13.8 volts DC to zero volts DC) The resonance flap is sprung open (by spring tension), allowing flow through both resonance tubes, increasing volume.
Originally Posted by seemyad
You hit the nail on the head Blubee.

The diaphragm (when vacuum is applied) and the spring are two opposing forces on the flap. The spring is why the flap is open when you hold the DISA in your hand.

From the videos I linked in a previous post (above) I can see the spring tension on the flap when the guy is forcing the flap closed. He then closes the flap by hand and puts his finger over a small hole where the diaphragm is located. The vacuum seal he creates with his finger forces the flap to remain closed against the tension of the spring.

The electrical portion merely creates/completes the path for the vacuum giving the diaphragm enough "suction" to force the flap close (opposing the spring tension). When you exceed X RPM the 12 VDC is removed thereby opening an "escape root" for the vacuum (basically allowing air into the diaphragm). The tension from the spring then forces the flap open.

When the RPM drops back below the threshold, the 12 VDC is reapplied to the solenoid which then closes the path to allow a vacuum to form again which forces the diaphragm to close the flap.

"As soon as the solenoid valve switches (on dropping below the switching speed) the vacuum reservoir and vacuum unit..." (I believe the vacuum unit to be where the spring and diaphragm are located) "...are reconnected and the connecting flap closed." NOTE: As I have not held a DISA in my hand yet I am unsure as to the location of the "vacuum reservoir".

There is much more to the DISA than meets the eye. Although the parts that comprise the DISA are not expensive individually, I can better appreciate the cost. The reality is it is amazing that so many plastic moving parts and the rubber diaphragm hold up as long as they do under such extreme pressure, vibration, and temperature variations (below freezing to above boiling point of H2O).

I no longer view the DISA as an overpriced cheap piece of plastic. It's moving parts appear to last over ten years and over 100,000 miles under extreme; pressure, vibrations, and temperature variation. The DISA alone is engineered better than most American cars (sad fact).

Also, normal rubber would dry up and crack within a year under these conditions yet the diaphragm retains its properties for a decade or more (hot or cold).

Blubee, there IS value in your desire to understand how stuff works. Thank you for always going that extra mile.

You gave me the missing clue when you mentioned the "magnetic switch". I have an extensive electronics background (which paid for my BMW) so that is all I needed to put the rest of the puzzle together. That's what I call "team work".
 
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