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I was getting ready to put the throttle body back on my car yesterday and thought I'd check the operation of the double throttle diaphragm - dead! I went to my spare throttle body - dead! I just checked with the dealer, and this thing is a whopping $90!
On a non turbo car the double throttle is spring loaded to the wide open position when the car is warm/hot or the diaphram is busted. Just FYI for whoever. Turbo's are different.
Uh, I dunno what kinda car you got, but I know on turbos, the thermowax prevents them from opening so you don't do anything stupid with the engine still cold. :P
On a non turbo car the double throttle is spring loaded to the wide open position when the car is warm/hot or the diaphram is busted. Just FYI for whoever. Turbo's are different.
Uh, I dunno what kinda car you got, but I know on turbos, the thermowax prevents them from opening so you don't do anything stupid with the engine still cold. :P
-Ted
I've turbo and non turbo. The outter secondary plates are SPRING LOADED open if the diaphram is busted or the engine is hot or warm. It's always been that way, always will be.
The turbo is different. I kinda remember writing that in my post above.
All automatics should be ignored. If we do maybe people will forget that MAZDA mistake.
Here's a Jpg of your normal, non-turbo double throttle diaphram and fully spring loaded open secondary throttle plates. I've never ever found a working double throttle diaphram in a wrecking yard in the last five years and I've better things to buy with nintey bucks than a diaphram.
I ain't gonna be buying a new one, that's for sure. A hub or ACV at $500 sounds like an absolute bargain compared to this!
I guess I just won't worry about it, but I will try to take apart my spare just for kicks. Besides, I can't remember exactly how long the secondaries are held closed (it's in the FSM), but it's not very long. Seconds, not minutes, IIRC.
Just wire it open and remember not to floor it as soon as its turned on. I did it and it runs fine.
Again...the double throttle diaphram has a spring the holds the outer throttle plates full open even if the diaphram is busted. There's no need to wire it open. It's a non-turbo double throttle diaphram.
I just ordered two used ones from Riggs Vintage Mazda, I asked them to test them both before shipping, let's see how that goes!
I received the two diaphragms; My testing hookup
one doesn't move the lever at all with my hand vacuum pump.
The other moves in a fat sixteenth, I believe it needs to move quite a bit more!
Do these diaphragms hold vacuum, or do they quickly bleed it off with a hand pump?
The manual says to apply 200 mm Hg and check that the secondary throttle valve is fully closed.
Riggs sent me some 2 second movies showing the lever moving about 1/4" in, then quickly moving out in-between pumping the handle quickly!
Is this showing a functional diaphragm?
Please straighten me out before I argue with Riggs about this.
They say that it needs to see a steady vacuum from a running engine to keep the lever in. A hand pump won't provide a steady pull.
That does not sound correct to me, but what do I know?
The hand vacuum pump is a good way to measure it. . . . .Don't release the handle on the hand vacuum pump doing the test. . Pump a bunch of times and hold the handle in on the last stroke. . . .The pump vents itself when released. {At least mine did.} The DTV unit should stay sucked in
In any case, this is what I did with my 86 N/A .. . I retrofitted it to another unit as I believe the existing unit is NLA. I'm surprised somebody found one for sale.
You have to make a simple sheet metal bracket to make it work.. . The angle bracket comes with the new unit and is re-used in this new assembly.
The hand vacuum pump is a good way to measure it. . . . .Don't release the handle on the hand vacuum pump doing the test. . Pump a bunch of times and hold the handle in on the last stroke. . . .The pump vents itself when released. {At least mine did.} The DTV unit should stay sucked in
In any case, this is what I did with my 86 N/A .. . I retrofitted it to another unit as I believe the existing unit is NLA. I'm surprised somebody found one for sale.
You have to make a simple sheet metal bracket to make it work.. . The angle bracket comes with the new unit and is re-used in this new assembly.
How did you find this diaphragm?
My only concern is that the spring tension is different from the stock part.
The workshop manual shows how to test if it fully closes the #2 secondary throttle plates at 200mm of vacuum.
Also, what good would a hand operated vacuum tester be if it released the vacuum on its own!
Mine has a release valve on the bottom opposite the gauge, I have to press it to release the vacuum when doing a test! That is if the part being tested holds a vacuum, that is the purpose of the vacuum testing pump. 
I found it searching for the NLA EGR valve and then I thought it might be the right size and stroke for the double throttle diaphragm
I am not sure if the OEM unit has a spring. It feels like the rebound is totally done by the rubber diaphragm.. . .I dunno, I've never cut it open.
I tested this unit with a hand vacuum pump and it sucks in around 8" vac. . ..Typically the Vac system on my 86 N/A runs around 16 to 20" during idle. . . .More than enough to pull in when the thermowax valve allows the vacuum condition.
The tricky part is getting the stroke and the play in the pin done right.. . .Bracket needs to be made right in order to accomplish this.
At the end of the day there needs to be force put on the vanes to keep them open when there is no vacuum applied. (i.e. warmed up). . And this force comes from the unit when there is no vacuum applied.. As you know, the thermowax valve controls the vacuum.
I put around 5k miles on this design and it works like it should. . .It retards the engine when cold.. . .Gives a place to land the vac line.
If the purpose is to go fast, just omit it. .. . I never noticed how much it retards the engine when cold until I made it work again.
Please explain what "It retards the engine when cold" for me?
I am trying to understand this system and I am bit confounded, I know that manifold vacuum is applied to the diaphragm when the coolant temperature is below 140 degrees F. Once it reaches above 140 the vacuum is blocked, and the throttle valves are held fully open.
My question is how the throttle valves behave as the engine warms up? Does it come into effect only on deceleration when the secondary throttle plates are closing? The dashpot slows their closing down, (To prevent bucking?) But at the same time the vacuum should be increasing in the diaphragm closing the valves? What does this accomplish? Also, why does the system use a delay valve in it?
Any info is appreciated! 
P.S. I am going to cut apart one of my diaphragms and determine how they function.
It doesn't retard anything. It restricts airflow until correct fuel can be calculated. Here's what's going on.
Our engines measure the airflow coming in two ways; the MAF sensor by the air filter, and calculations based on air-pressure and intake air temp sensor at the throttle body. Airflow at idle, and low throttle conditions is measured using the MAF sensor. As covered in a previous post, idle and low-throttle airflow is fairly minimal, so you need a narrower range, high resolution sensor. Under higher throttle conditions, the MAF sensor maxes out and the ECU still needs to calculate the correct fuel mix. It does so by assuming an airflow based on intake pressure and temperature. This is where the intake air temp at the throttle body comes in. This sensor has to be heated for it to be in the useful range. The intake air flowing over the heated sensor cools it and changes the resistance. Sensors in other vehicles may have a heating element on them, bug for our purposes, ours are heated via the metal in the throttle body. There are two coolant hoses to circulate coolant through the throttle body to heat it up. Once the throttle body is at temp, the sensor is in the proper range to measure accurately. The thermowax vacuum valve is a mechanical means of ensuring that the sensor is able to reach temperature before the engine goes under full load. With the secondary throttle bores blocked until the sensor heats up, the narrow range air calculations are performed based on the airflow from the primary throttle bore only.
Yes there will be vacuum behind those secondary plates, but that doesn't affect anything at all. Those intake runners just aren't being used at that time. The vacuum source for the diaphragm comes off of the secondary throttle bores. The primary throttle bore loses vacuum when it opens, which would defeat the purpose. While the main secondary plates do open with the primary, the diaphragm controlled secondary plates are placed upstream of the main secondary plates so that vacuum is maintained through all throttle positions until the thermowax allows it to open up. They stay shut until the throttle body is warmed up, and will open and close with the main secondary plates once the thermowax valve has decoupled the diaphragm from the system. Once the throttle body is hot, the diaphragm goes to rest and does nothing.
A couple important notes here:
Do not block off the coolant lines to the throttle body. They are there to heat up the intake air temp sensor. Also, the spacer block between the UIM and the throttle body acts as an insulator, so less heat transmits from the keg to the throttle body and the coolant keeps the sensor at a more stable reference point.
This post describes the NA setup, and a simplified portion of the Turbo II setup. The Turbo II has a couple other components such as the MAP sensor and an intake air temp sensor in the MAF as well as the one at the throttle body. Those allow the ECU to account for the compressor changing the temperature of the intake air.
It doesn't retard anything. It restricts airflow until correct fuel can be calculated. Here's what's going on.
Our engines measure the airflow coming in two ways; the MAF sensor by the air filter, and calculations based on air-pressure and intake air temp sensor at the throttle body. Airflow at idle, and low throttle conditions is measured using the MAF sensor. As covered in a previous post, idle and low-throttle airflow is fairly minimal, so you need a narrower range, high resolution sensor. Under higher throttle conditions, the MAF sensor maxes out and the ECU still needs to calculate the correct fuel mix. It does so by assuming an airflow based on intake pressure and temperature. This is where the intake air temp at the throttle body comes in. This sensor has to be heated for it to be in the useful range. The intake air flowing over the heated sensor cools it and changes the resistance. Sensors in other vehicles may have a heating element on them, bug for our purposes, ours are heated via the metal in the throttle body. There are two coolant hoses to circulate coolant through the throttle body to heat it up. Once the throttle body is at temp, the sensor is in the proper range to measure accurately. The thermowax vacuum valve is a mechanical means of ensuring that the sensor is able to reach temperature before the engine goes under full load. With the secondary throttle bores blocked until the sensor heats up, the narrow range air calculations are performed based on the airflow from the primary throttle bore only.
Yes there will be vacuum behind those secondary plates, but that doesn't affect anything at all. Those intake runners just aren't being used at that time. The vacuum source for the diaphragm comes off of the secondary throttle bores. The primary throttle bore loses vacuum when it opens, which would defeat the purpose. While the main secondary plates do open with the primary, the diaphragm controlled secondary plates are placed upstream of the main secondary plates so that vacuum is maintained through all throttle positions until the thermowax allows it to open up. They stay shut until the throttle body is warmed up, and will open and close with the main secondary plates once the thermowax valve has decoupled the diaphragm from the system. Once the throttle body is hot, the diaphragm goes to rest and does nothing.
A couple important notes here:
Do not block off the coolant lines to the throttle body. They are there to heat up the intake air temp sensor. Also, the spacer block between the UIM and the throttle body acts as an insulator, so less heat transmits from the keg to the throttle body and the coolant keeps the sensor at a more stable reference point.
This post describes the NA setup, and a simplified portion of the Turbo II setup. The Turbo II has a couple other components such as the MAP sensor and an intake air temp sensor in the MAF as well as the one at the throttle body. Those allow the ECU to account for the compressor changing the temperature of the intake air.
All due respect, but I don't think that's accurate. FCs use MAF based fuel calculation under all conditions. I don't think there's any situation (on a stock car) in which the MAF is maxed out. Also, the IAT sensor in the dynamic chamber is used for calculating BAC valve duty only (to compensate for less dense air at higher intake temperatures). The one inside the MAF is for fuel corrections.
The vacuum diaphragm being discussed here is purely to slow transitions in air when the engine is cold. Your description of the way that the diaphragm system works is 100% correct, but its only function is to slow throttle transitions (probably to prevent a transient lean condition). When the car is cold and you blip the throttle, the mechanical secondaries open instantly but the vacuum controlled secondaries will slowly open (slowly still being < 1s) as the vacuum in the intake drops and the diaphragm returns to resting position. Once the engine is hot there is no vacuum to the diaphragm at all and the system is disabled.
Here's the relevant page describing this function in the training manual:
As far as fuel calculations, it's MAF based:
And it uses the other sensors for "corrections" but, the training manual is a bit unclear as to how:
(For some reason the "Australia Only" model in the manual seems to correspond to USDM NA FCs)
So the MAP sensor is used for compensations of some sort. I'm just not sure what. The most confusing part to me is the "output increase" - it's very vague and the only description is "To increase output"
