Strange results from a simple test of the M54 DISA valve today

Would someone else with the M54 correlate my test results against theirs?

Requirements:
- Voltmeter & small wires as test leads
- An assistant to rev the engine over 3,750 RPM
- 12 volt source (I used a battery charger but one can tap off of the nearby engine positive terminal)

Results:
TEST 1: CONFIRMED: Theory says the DISA lever will move aft with ~12 volts DC and will snap back at zero volts DC; I saw this clearly in my tests.

TEST 2: Inconclusive: Theory says the voltage should drop from ~12 volts to zero volts at 3,750 RPM; I never saw the voltage drop; mine stayed at about 13.8 volts DC on my digital multimeter. Perhaps it's a 'momentary' switch? If so, an analog meter might have shown the switchover more clearly.

TEST 3: Inconclusive: Theory says the lever should move aft all-or-nothing at 3,750 RPM and stay there; out of ten attempts, only twice did the lever move; and even then, it appeared to move aft all the way only momentarily and way before 3750 RPM according to my assistant.

Q: Would others kindly run these three five-minute DISA tests & let us know their results?

TEST 1: DISA 12 volt DC OPERATIONAL TEST:

1. With whiteout, place a dot on the DISA valve external lever
2. Also mark the positive and negative sides of the DISA connector
   • The positive side is the edge toward the front of the vehicle
   • The negative side is the edge toward the rear of the vehicle
3. With the ignition off, remove the DISA harness connector
4. Place 12volts DC across the DISA terminals (red in front, black in rear)
   • I used my battery charger with a wire in the alligator jaws to make the connection
5. The lever should move toward the rear whenever innervated by the 12 volts DC

TEST 2: DISA 12 VOLT HARNESS SIGNAL TEST:

1. With the engine off, remove the DISA harness connector
2. Connect your voltmeter to the harness connector terminals
   • Place a red insulated wire in the positive terminal of the DISA harness connector
   • Place a black insulated wire in the negative terminal of the DISA harness connector
3. Start the engine and idle; you should measure 12 volts DC
4. Have an assistant rev the engine to 4000 RPM; at 3,750 RPM you should see the voltage drop to zero volts DC

TEST 3: DISA OPERATIONAL TEST:

1. With whiteout, place a dot on the DISA external lever arm
2. Ask an assistant to start the engine and allow it to idle
   • The DISA lever should not move
3. Then ask the assistant to rev the engine to 4,000 RPM
   • The DISA lever should move at 3,750 RPM

REFERENCE DISA OPERATIONAL THEORY:

Originally Posted by AnotherGeezer

"The disa valve has an outer seal (inside the manifold) and a diaphragm inside the valve itself. The valve is constantly fed 12 volts during normal throttle operation and then open circuits on higher RPM and throttle opening. This de-energizes the coil which stops the manifold vacuum from reaching the diaphragm. The butterfly then springs open."

Originally Posted by gtxragtop;6369350[I

In the case of the DISA, it works off controlled vacuum. The 2 wires on the DISA are connected to a vacuum solenoid. It either blocks the passage of vacuum or allows it based upon the commands from the ECM[/i].

Originally Posted by pshovest

The mystery to me was the vacuum source. I had my M54 DISA out for inspection recently and discovered the 1/16" port.

Originally Posted by pshovest

The DISA flapper is either fully open or fully closed. There is no intermediate position on a properly working DISA valve. A DME controlled solenoid uses manifold vacuum to close DISA flapper and spring action to open the DISA flapper.

Originally Posted by bluebee

Would someone else with the M54 correlate my test results against theirs?

I ran the following three tests with the following (inconclusive) results:
TEST 1: Conclusive: The DISA lever moved with 12 volt innervation.
TEST 2: Inconclusive: I never saw the voltage drop from 12 volts at 3750 RPM and above.
TEST 3: Inconclusive: Out of ten attempts, only twice did the lever move; and even then, it appeared to move only momentarily and way before 3750 RPM according to my assistant.

Q: Would others kindly run these three tests & let us know their results?

TEST 1: DISA 12 volt DC OPERATIONAL TEST:

1. With whiteout, place a dot on the DISA valve external lever
2. Also mark the positive and negative sides of the DISA connector
   • The positive side is the edge toward the front of the vehicle
   • The negative side is the edge toward the rear of the vehicle
3. With the ignition off, remove the DISA harness connector
4. Place 12volts DC across the DISA terminals (red in front, black in rear)
   • I used my battery charger with a wire in the alligator jaws to make the connection
5. The lever should move toward the rear whenever innervated by the 12 volts DC

TEST 2: DISA 12 VOLT HARNESS SIGNAL TEST:

1. With the engine off, remove the DISA harness connector
2. Connect your voltmeter to the harness connector terminals
   • Place a red insulated wire in the positive terminal of the DISA harness connector
   • Place a black insulated wire in the negative terminal of the DISA harness connector
3. Start the engine and idle; you should measure 12 volts DC
4. Have an assistant rev the engine to 4000 RPM; at 3,750 RPM you should see the voltage drop to zero volts DC

TEST 3: DISA OPERATIONAL TEST:

1. With whiteout, place a dot on the DISA external lever arm
2. Ask an assistant to start the engine and allow it to idle
   • The DISA lever should not move
3. Then ask the assistant to rev the engine to 4,000 RPM
   • The DISA lever should move at 3,750 RPM

REFERENCE DISA OPERATIONAL THEORY:

Somebody please answer this. I am all verklempt.

Replaced mine this weekend and noticed a very positive result.

I've moved on.

Next stop, Dinan Stage 2 suspension upgrade.

Originally Posted by AnotherGeezer

I've moved on

Everybody is different.

I prefer to attempt to understand HOW the device operates ... and then to form a test of that operation.

If it fails that test, then I simply replace; but for two reasons I don't want to simply replace the parts willy nilly:

1. A visual inspection showed it to be in good shape
2. Nobody will learn anything if I simply replace it.

Together, if we test our DISA valves functionally, we all can come up with a great test procedure for others to follow in our footsteps.

Hm, interesting. I don't have a DMM but I'll give it a shot in my car later today, if I can convince the wife to push the gas pedal….too bad the throttle is so buried under the manifold or I could do it myself!

Originally Posted by bluebee

Everybody is different.

I prefer to attempt to understand HOW the device operates ... and then to form a test of that operation.

I prefer to not beat a dead horse but everybody is different.

The only real way to test for DISA valve functionality without simply removing it is via engine diagnostic software. There is no simple external test other than removing the entire valve and eyeballing it. That's the old school way of doing it.

Making markings on certain components and revving the engine is fine, but it's apparently a hit-and-miss approach that yields more questions than answers...as evidenced by the copious volumes of repetitive information on this rather simple issue.

Bottom line is, the DISA valve either works or it doesn't and attempting to repair a part like that is a fool's errand.. If you're unsure if yours is cooked, remove it and look at it. Even if it still works, check to see if the pin is loose and ready to fly into the intake. The benefit of simply replacing this pain-in-the-butt part far outweighs any money saved by trying to repair it. If you think you need one, you probably do.

Originally Posted by AnotherGeezer

I prefer to not beat a dead horse but everybody is different.

The only real way to test for DISA valve functionality without simply removing it is via engine diagnostic software. There is no simple external test other than removing the entire valve and eyeballing it. That's the old school way of doing it.

Making markings on certain components and revving the engine is fine, but it's apparently a hit-and-miss approach that yields more questions than answers...as evidenced by the copious volumes of repetitive information on this rather simple issue.

Bottom line is, the DISA valve either works or it doesn't and attempting to repair a part like that is a fool's errand.. If you're unsure if yours is cooked, remove it and look at it. Even if it still works, check to see if the pin is loose and ready to fly into the intake. The benefit of simply replacing this pain-in-the-butt part far outweighs any money saved by trying to repair it. If you think you need one, you probably do.

Couldn't have said it better myself........

I strongly suspect that the DISA valve movement is controlled by the engine management system by more than RPM.

I replaced mine. Had no real symptoms other than a momentary flat spot/power drop at 2/3 throttle when accelerating and the RPM hit
somewhere around 3500-4000 RPM. Some folks stated this was a VANOS seal issue. Nope it was not though my seals were
hard as a rock. DISA solved the flat spot/power drop.

Thinking more about a vacuum leak, if the "yellow" DISA flap actuator or the vacuum dashpot has a leak, it would be difficult to
diagnose. My yellow flap actuator fit into the housing seemed good, hence I would not suspect leakage.

Ignoring the leak issue for a moment, if the one-way vacuum valve does not work properly, there will be no vacuum to actuate
the valve under a load when vacuum drops when the throttle is opened more than 1/2 way.

Originally Posted by gtxragtop

I strongly suspect that the DISA valve movement is controlled by the engine management system by more than RPM.

Given the strange workings, I suspect the same.

The only way we'll figure out how the DISA works is by using our innate youthful curiosity & intelligence. It takes neither to replace; both to understand well enough to test.

Originally Posted by gtxragtop

if the one-way vacuum valve does not work properly, there will be no vacuum to actuate

That's interesting! There must be a simple way to test that one-way vacuum valve. Perhaps we can remove it and blow into it either way.

Do you think it's removable without destroying the DISA itself?

Still waiting for mine to be delivered. If one had a switch mode power supply one could dial the voltage up and down with a pot to view the effects on the unit. I'll make a quick search for a schematic just to see whats out there. That being said consider this:

The electrical connection may exist to send sensor information vs control the unit. As a former Avionics Technician on 7XX series aircraft we tested moving surface indicators i.e. flaps, slats, aileron, trim and so forth. Part of the test consisted of taking voltage (or current) readings while moving the surface to different positions (degrees). 10 degrees should send out X amount of voltage (or current) and so forth. So there was a power source being sent to the unit that was attached to the moving surface. However the surface itself was moved via hydraulic pressure not by the sensing unit attached to it.

Is it possible that the DISA valve is moved via vacuum or some other environmental force and the electrical connection is simply telling the ECU the real time position of the vein?

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Originally Posted by seemyad

If one had a switch mode power supply one could dial the voltage up and down with a pot to view the effects on the unit.

I don't think that is necessary 'if' the connector is simply the alternator voltage input TO the DISA valve.

AFAIK, it either has ~13.8 volts on it ... or it doesn't.

When it has ~13.8 volts on it, the DISA is in the relaxed position due to mechanical spring pressure; when that voltage drops to zero volts, the DISA valve stem is pulled backward (opening the flap inside the intake manifold).

The vacuum is purportedly coming from a small one-way vent valve in the side of the DISA closest to the engine as shown in this thread:
- DISA Autopsy

Originally Posted by seemyad

Is it possible that the DISA valve is moved via vacuum or some other environmental force and the electrical connection is simply telling the ECU the real time position of the vein?

I still don't fundamentally understand how & when the DISA actually 'gets' the vacuum through that port in the photo above...

Originally Posted by bluebee

I don't think that is necessary 'if' the connector is simply the alternator voltage input TO the DISA valve.

AFAIK, it either has ~13.8 volts on it ... or it doesn't.

When it has ~13.8 volts on it, the DISA is in the relaxed position due to mechanical spring pressure; when that voltage drops to zero volts, the DISA valve stem is pulled backward (opening the flap inside the intake manifold).

The vacuum is purportedly coming from a small one-way vent valve in the side of the DISA closest to the engine as shown in this thread:
- DISA Autopsy




I still don't fundamentally understand how & when the DISA actually 'gets' the vacuum through that port in the photo above...

There is a 1/16" hole on the other side of that port. It gets vacuum from the manifold.

Thanks for the intel Blubee. That makes sense concerning the voltage. Also, I found this simple youtube video about the DISA.

Testing the Seal


Fixing a Broke DISA (this guy glues his). Video shows points of failure toward the middle.

This also purports to show how the DISA works.
Notice that the RED valve is the DISA valve.
Also notice the yellow vacuum and the black magnetic valve?

QUESTION:
Where is that magnetic valve?

Originally Posted by bluebee

This also purports to show how the DISA works.
Notice that the RED valve is the DISA valve.
Also notice the yellow vacuum and the black magnetic valve?

QUESTION:
Where is that magnetic valve?

Considering your earlier intel regarding the voltage, I surmise the "magnetic valve" could be something as simple as an iron rod with wire coiled around it.

12VDC could energize the coiled wires to create a magnetic field used to pull some mechanism (open or close) inside the housing of the DISA. This is the simplest way the voltage can be used. Perhaps the vacuum actually opens and closes the circuit used to energize the magnetic valve with the supplied voltage OR perhaps the vacuum is used to regulate how far the vein will open once the magnet is energized.

This is 100% conjecture on my part based on electronic theory and ZERO experience with the DISA.

If I had the tools I'd dissect mine after the new one is installed.

Here is a DISA block diagram: (scroll to shrink and/or enlarge)
http://wds.spaghetticoder.org/us/svg...36.svg?m=e3902

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=== EDIT - Pay Dirt !!! === The following description works well with the images Blubee provided right above this post


HOW IT WORKS -

Individual Control Intake System (DISA)


Function

Periodic pressure fluctuations are produced in the intake pipe by the induction strokes of the cylinders. These pressure waves run through the intake tube and are reflected at the closed inlet valves. The intake tube length precisely adapted to the valve timing ensures that a pressure peak of the reflected air wave reaches the inlet valve just before the end of its opening range. A post-charging effect is achieved in this way. This post-charging effect conveys a larger volume of fresh mixture into the cylinder.

DISA utilizes the advantages of short and long intake pipes.

Short intake pipes or intake pipes with a large diameter have the effect of producing higher output values in the upper engine speed range together with lower torque values in the medium engine speed range. Long intake pipes or intake pipes with a small diameter develop high torque in the medium engine speed range.

Operating principle

A headpipe is arranged ahead of the oscillating tubes of the two cylinder banks.

When the connecting flap valve is closed , the headpipe and oscillating tube together act as a long intake pipe. The pulsating gas column produces a distinct increase in torque in the medium engine speed range.

The connecting flap between the two cylinder banks is opened in order to increase the output in the upper engine speed range. As a result, the dynamics of the headpipes is reduced to a large extent. The short oscillating tubes which are now effective enable higher output values in the upper engine speed range.

The vacuum tank is evacuated by the vacuum applied in the intake pipe in the partial load range. The connecting flap is closed with the aid of the vacuum unit and the pneumatic actuator.

===> MEAT AND POTATOES HERE BLUBEE ===> If the switching speed is exceeded, the DME control unit deactivates the solenoid valve, i.e. it is switched off. As a result, the vacuum unit is aerated and the flap opened.

As soon as the solenoid valve switches (on dropping below the switching speed) the vacuum reservoir and vacuum unit are reconnected and the connecting flap closed.

The switching speeds for activation and deactivation are shifted with respect to each other (hysteresis) in order to avoid opening and closing in rapid succession.

This control configuration ensures that the connecting flap always remains open in the event of a fault in the electropneumatic flap operation. This ensures the complete engine output is available in the upper engine speed range (e.g. for overtaking). The basic setting of the flap is therefore "open".

The flap is returned or opened by means of two springs:

- A torsion spring on the flap shaft

- A coil spring in the diaphragm cell

The solenoid valve is activated directly via a powerful output stage in the DME control unit.




Source of information above = http://wds.spaghetticoder.org/us/zin...1214_M0DIS.htm






CONCLUSION:

Based on what I just read above it appears the "magnetic valve" aka "solenoid" closes allowing the vacuum to build and close the flap. When it is de-energized the valve opens which releases the vacuum and the spring opens the flap. The flap appears to remain in a "normally open" position until the "magnetic valve" aka "solenoid" creates the condition for the vacuum to build and pull the flap close. The 12VDC controls the solenoid aka "magnetic valve".

Talk about engineering!!! You have to design the size and shape of the intake manifold in such a manner that the DISA will have the desired effect at the desired RPM. These guys don't play when it comes to BMW. WOW!

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Originally Posted by seemyad

The flap appears to remain in a "normally open" position until the "magnetic valve" aka "solenoid" creates the condition for the vacuum to build and pull the flap close. The 12VDC controls the solenoid aka "magnetic valve"

Verrrry interesting!

There is more over here, in pages 42 to 44:
- m54x5[1].pdf

Note: My clarifications are in red; otherwise, it's verbatim from that document.

Also notice the use of the word "vacuum accumulator" which, somehow, helps to 'close' the valve (but why isn't the 12 volt DC magnetic solenoid enough to close the valve on it's own?).

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.

BTW, here is the DISA electrical block diagram referenced above:

Originally Posted by seemyad

Here is a DISA block diagram: (scroll to shrink and/or enlarge)
http://wds.spaghetticoder.org/us/svg...36.svg?m=e3902

Originally Posted by bluebee

Verrrry interesting!

There is more over here, in pages 42 to 44:
- m54x5[1].pdf

It begins to make sense. Airflow dynamics are being manipulated to create a "wave" for increased torque (valve closed). At higher RPMs volume is increased for more power by turning one path to the cylinders into two paths. You lose the directional wave but you have more air (volume) due to the additional passage way when the flap is open.

Ingenious!!! I never considered the utilization of resonant waves of air to manipulate engine performance. Makes one appreciate why the high sticker price. These are not just-another-engine. I wondered how they could make such a heavy car seem so light on it's feet in the full range of speed.

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Originally Posted by seemyad

It begins to make sense.

It's only barely beginning to make sense to me!

The part that confuses me is the purpose of the 'vacuum accumulator'.

Here are two opposing observations:
a) When I applied 12 volts DC to the DISA, even with the engine off, the lever clearly and forcefully actuated. We now know that this actuated a magnetic solenoid which 'closed' the flap against the spring mechanical pressure.

b) The description above clearly says this ... but it also adds "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"

So, the critical question is WHY do we even need the one-way check valve for the vacuum accumultor to accumulate vacuum.

Q: Why isn't the force of the magnetic solenoid enough to close the flap?

Here is my hazard of a guess at what happens:

At idle, there is 12 volts DC at the DISA valve. This clearly (and forcefully) pulls the lever backward ... but ... maybe ... just maybe ... that's NOT ENOUGH FORCE??? to close the flap tightly.

Maybe that pulling back of the lever simply allows engine vacuum to get to the "vacuum accumulator" one-way check valve.

Maybe that's all the magnetic solenoid accomplishes (perhaps it moves a blocking object from covering the one-way check valve?)?

Then, once the 12 volts moves the lever backward which (I'm guessing) uncovers the one-way check valve ... then (and only then?) can the vacuum begin to "accumulate", which (somehow) actually forces the flap closed (i.e., into the vertical position against spring tension).

So, in that hypothetical scenario, the 12 volts merely allows the vacuum port to be 'uncovered'. Once uncovered, the one-way check valve allows vacuum to accumulate ... which ... in time ... closes the flap. ???

Why else would the DISA require BOTH a magnetic solenoid AND a vacuum accumulator to close the flap?

Does anyone have a better idea of why the magnetic solenoid isn't enough, on its own, to close the valve (i.e., why do we need vacuum accumulation to close the valve?)?

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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Originally Posted by seemyad

The electrical portion merely creates/completes the path for the vacuum giving the diaphragm enough "suction" to force the flap close

Wonderful explanation!

You tied together the 'finger hole' in the video with this whole operation. That's teamwork!

I don't think ANYONE actually understood, until now, HOW the DISA valve actually closed!
- When does the intake manifold adjustor (DISA Valve) close?

In fact, despite tons of threads, I don't think anyone really knew what you just said!

• - Strange results from a simple test of the M54 DISA valve today
• - When does the intake manifold adjustor (DISA Valve) close?
• - How the DISA Works
• - DISA Autopsy
• etc.

Originally Posted by seemyad

I am unsure as to the location of the "vacuum reservoir"

Some say it's the rectangular box itself. That needs to be proven/disproven though.

Originally Posted by seemyad

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

Thanks for the support. It 'was' dismaying to see others say, in effect, "just replace the damn thing and stop asking questions".

I wanted to say that only 1% of the people out there actually add value to figure out HOW something works in order to better understand how to test it when it doesn't work. But that is lost on 99% of the people who only care to replace the part, whether it's good or bad.

Originally Posted by seemyad

You gave me the missing clue when you mentioned the "magnetic switch".

And RDL gave us that clue in the first place. This is total teamwork. Tribal effort at its finest!

To help others, I just now added your response to the canonical DISA thread:
- How the DISA Works

EDIT: BTW, the fact there is a group buy with almost 100 people on it, means we just might get that 1% who take theirs apart and prove or disprove all that we've surmised, as a team:
- DISA Valve Pricing - Group Buy - ORDERING INFO

Over in that thread, I posted a request for 1% of the 100 people buying a new DISA in the group buy to autopsy it specifically to test the hypothesis.

Here is my restatement, in layman's terms, how I think it operates (as always, please correct).

Notice the problematic step of HOW the accumulated vacuum dissipates...

Originally Posted by bluebee

out of the 100 or so takers for this deal, will at least 1% of you take the time and effort to autopsy your DISA specifically to prove or disprove the magnetic solenoid vacuum accumulator one-way check valve theory?

Here's the theory, in a nutshell (see details in that thread):

1. The DISA, at idle, has 12 volts actuating it.
2. This pulls back a magnetic solenoid actuated lever, which (apparently) uncovers a one-way vacuum check valve which is vented to the outside by a 1/16" hole drilled in the DISA body.
3. This one-way vacuum check valve "accumulates" vacuum (apparently in the square box) until the DISA flap valve closes (due to the vacuum - not due directly to the magnetic solenoid).
4. When a set of higher-rpm conditions (temperature & RPM) are reached, the 12 volts signal goes to zero volts.
5. This (somehow) covers up the check valve ... which (somehow) allows the accumulated vacuum to dissipate (which it won't do if you hold your finger on the outside hole as shown in the videos).
6. When the accumulated vacuum has dissipated to a weak point, the spring-loaded flap returns to its normal position (i.e., open).

Originally Posted by bluebee

Over in that thread, I posted a request for 1% of the 100 people buying a new DISA in the group buy to autopsy it specifically to test the hypothesis.

Here is my restatement, in layman's terms, how I think it operates (as always, please correct).

Notice the problematic step of HOW the accumulated vacuum dissipates...

[/LIST]

You may have steps 2 and 5 crossed. From observing the YouTube video I surmise the energized state closes the vent hole (allowing the vacuum to build) while simultaneously opening a valve connecting the vacuum reservoir to the diaphragm. The de-energized state opens the vent hole releasing the vacuum) while simultaneously closing the air valve disconnecting the vacuum reservoir.


Just a guess on my part. Need to cut one open to see the mechanism.

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Originally Posted by seemyad

You may have steps 2 and 5 crossed.

Just returned from Tahoe.

Based on this thread, I think my whole scenario above is wrong about what actually pulls the flap closed against mechanical spring pressure:
- DISA autopsy

Originally Posted by bluebee

Is this a decent proposal for testing the DISA diaphragm for integrity?

1. Remove DISA valve (two T40 torx screws)
2. Manually set the flap into the closed position (against spring pressure)
3. Seal the 1/16" vacuum hose with your finger
4. If the DISA flap moves afterward, the diaphragm is leaking

Originally Posted by bluebee

How does this sound?

• Idle condition ...
  • 12VDC present, air valve opens, vacuum accumulates, flap pulls shut (vertical) against the force of the mechanical spring
• At 3,750 RPM ...
  • 0VDC present, air valve shuts, vacuum dissipates?, flap swings open (horizontal) due to the mechanical spring
• Back below 3,750 RPM ...
  • 12VDC present, air valve pulls open, vacuum again accumulates, flap pulls shut (vertical) against the force of the mechanical spring

QUESTION: What makes the vacuum dissipate when the air valve shuts?

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Originally Posted by bluebee

Just returned from Tahoe.

Welcome back!

I lived in Stockton CA for 6 months installing a new RADAR system at their airport. I drove up to Tahoe two or three times. The winding road up the mountain is beautiful (and scary at times). I love the scenery in Tahoe.

Based on this thread, I think my whole scenario above is wrong about what actually pulls the flap closed against mechanical spring pressure:
- DISA autopsy

Please provide input to my new DISA post:

How To Check Your DISA - 4 (fairly) Simple Checks
http://www.bimmerfest.com/forums/sho...d.php?t=575367


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