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Discussion Starter · #1 ·
Bought one, installed it, not sure if i'm happy or not.

Hopefully a few of you have done this before and will have some guesses as to what's wrong and why it's doing what it is.

Took off the old small one, put on the older larger RX-7 one. No leaks in the intake, everything is fine. Reset the ECU.

Idle's better than before.
From 2k RPM - 3k RPM - It's bogged down. Probably slower than an LX.
From 3k-4.5k - Normal, don't notice a difference.
From 4.5k-5.5k - Bogs back down. Kinda like anti-v-tec.
From 5.5k-7.?k - Screams. Alot of improvement. Kinda like v-tec. :)

Also, the throttle response has been shot all to hell. ANYWHERE in the RPM band, if i floor it, it stutters/slows down for a few secs, then goes. Once the pedal hits the floor, it's like i take my foot OFF of the gas for a sec. or 2, THEN it goes. Get what i'm sayin'? It only does this while in gear.. while in nuetral, the engine revs like normal.

Also, it flutters while holding the gas pedal still.. while cruising down the highway, it will increase/decrease in speed all by itself, and occasianally, it will act like i completely took my foot off of the gas, and the check engine light will come on.. then i floor it for a sec and everything's fine and dandy again..

Any guesses? I'm stumped. It worked fine on the car i got it off of. I'm about to put my small one back on just for driveability.. the top end power almost isn't worth it..
 

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First thing I would do is install the smaller one for now. If you still have the problems, then it's not the VAF (obviously), and if they go away, then it's obviously the VAF. I say this only because it sounds like a vacuum hose leak or intake tear to me. I could be way off base, but you never know.

Also, does the sensor itself send the same type of signal to the ECU? That may be the problem as well, though I don't know the technical specs of either of the VAF's, so I couldn't tell you.
 

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Discussion Starter · #3 ·
well i would, but putting the smaller one back in isn't really an easy task.. the in/out connectors on both ends of the smaller and larger VAM's are different sizes, so i have to find hoses to fit, re-silicone the adapter plate, ect.

i am 100% sure there are no tears in the intake tube or any vacuum hoses. i have replaced all of the vacuum hoses within the past few months, and i had the whole intake hose off a few times recently, and it's no different than before. :) also, it's not making any "hissing" sounds associated with either of the above.

the signal is sends is the only thing i'm concerned about, and this is kinda what i was wondering if anyone knew about. i'm sure PHYSICALLY the entire system is fine, and i'm pretty sure the VAM itstelf is operating properly.. i just want to know if there is something that needs to be done wiring-wise that i left out, or if this was normal with the larger VAM.
 

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You do know you have to tune the larger RX-7 VAF for your car rght?

you pop off the black cover and turn the dial a couple clicks

NOt sure which direction, theres a how-to on the site somewhere but without a tune yes, yer motor will run like shite

Once its tuned though, nice improvement in pull about 5K

R.
 

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DONT GET DISCOURAGED!!

its apparently really easy on these ones, I mean I don't know how much, if at all, VAM's differ from thunderbird to RX-7 but the how-to, damned if I can find it describes it as a pretty simple process


R.
 

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Damn... I really wish my stupid sister didn't have to take my computer to college- I had breakdown pics of the VAF- detailed pics of exactly what to do, and what every part in it was and what it did. Anyway...

There is a black cover on the top, of course. Take a nice sharp exacto knife and cut through the sillicone along the perimeter of the black lid. Since the sillicone is easy to cut through, and the lid is plastic and harder to cut through, you want to cut ONLY through the sillicone, and not the plastic. The plastic has a flare on the lower edge, so don't worry about about the tip of the knife going too far down and cutting any electronics, because it wont happen as long as you don't press too hard.
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This is what I have been told by darryl (mazdaspeedwest) on his rx-7 VAF how-to page: (in my own words)
Anyway, take a small screwdriver once you get the sillicone cut along the perimeter and pry the lid up and out. Once you get it off, you see that the entire assembly is based on a variable resistor, with varying resistance depending on the angle of the vane. What you do is you have to "re-zero" the vane. There are a series of notches along the outer edge of this ring, and a little clippy thing that fits into these notches that attaches directly to the vane. You have to unclip the clip and move along the notches until you get about a 0.5V idle voltage from the O2 sensor on your exhaust manifold.
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On another note, there is a valve (it's actually a piston) and it controls the volume of flow that is UNMETERED by the vane within the unit. It's a bypass air valve. It is a cylinder with a metal cap (that must be drilled out to access the screw) located on the upper, filter-side of the VAF.

I am not a certified auto mechanic, but I am a mechanical engineer and I tend to have a good sense of how systems work.

The thing is, the RX-7 and the 1.8L BP engine are two different engines. The ratio of air to fuel at, say 1200rpms may be (and probably is) different on the RX-7 than the a/f ratio needed by the EGT @ 1200rpms. On top of that, the RX-7 is a friggin rotary! I mean... it's a completely different engine! For all we know, the RX-7 meter may get really rich as the vane angle approaches 10 degrees and then lean out at 25 degrees... we really honestly don't know.

However, what COULD happen is that the resistance is linear and directly proportional to the angle of the vane with respect to the unit. What this means is that plotting resistance versus vane angle gives a line with a constant slope... or if you will, a graph with dy/dx equal to a constant. What I am saying is that the relationship between resistance versus vane angle MAY NOT be linear like we all assume. It may be exponential, etc, depending on how the VAF was designed for the RX-7 and the EGT.

However... if they are BOTH linear and have the same min and max angle resistances, then the ECU will decide the a/f, and thus the RX-7 and EGT VAF are both freely interchangable.

The concepts I discussed really aren't too far out... so don't think that I'm just talking out of my a$$, because I'm not.
 
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