Jersey Posted September 20, 2003 Share Posted September 20, 2003 Hey all. Referencing a '82ZXT. Does anyone know what the VCV is for? Thanks. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted September 20, 2003 Share Posted September 20, 2003 I believe it controls other valves such as the idle control... it meters the amount of vacuum to the valves it connects to. Quote Link to comment Share on other sites More sharing options...
Jersey Posted September 20, 2003 Author Share Posted September 20, 2003 Idle control, as in AAC (Auxillary Air Control) valve? The AAC is the only "valve" that is directly connected in the T mess of hoses on top of the intake and the AAC gets controlled by the VCM (Vacuum Control Modulator) This VCV is also connected to the 3/4" nipple off of the J-pipe and to the Air Regulator. The direction of the valve is that, it opens and allows air into the intake when pressure is applied from the top or a great amount of vacuum is in the intake and pulls it open, allowing air in. I just have no idea what this is for and what situation would cause it to open. Appreciate the response 525. Any other ideas out there? Quote Link to comment Share on other sites More sharing options...
Guest szlash280z Posted September 20, 2003 Share Posted September 20, 2003 it's just there to make you ask questions. now leave it alone! I am just kidding. I don't know what it is for. Quote Link to comment Share on other sites More sharing options...
Cody 82 ZXT Posted September 21, 2003 Share Posted September 21, 2003 I know one of them controls the EGR functions. Quote Link to comment Share on other sites More sharing options...
Jersey Posted September 21, 2003 Author Share Posted September 21, 2003 That aint right szlash! Cody, the VCM controls the AAC and EGR. Come on guys, someone out there HAS to know what this VCV's purpose is??? Quote Link to comment Share on other sites More sharing options...
Jersey Posted September 21, 2003 Author Share Posted September 21, 2003 Ok, i though about it more and i have an idea - When you snap the throttle plate closed with a good load on the motor, instead of the vacuum in the intake going to 50hg's, it only goes to say 28hg because this VCV opens and "controls" the amount of vacuum to a tolerable rate by letting air from the J-pipe in. Whattya say? Quote Link to comment Share on other sites More sharing options...
Cody 82 ZXT Posted September 21, 2003 Share Posted September 21, 2003 I really wish I had an exact diagram for how the vacum lines go and exactly what they do. I have studied it some but, it's been about two years siince I tried to have it running perfectly with those dodads hooked up. Now I don't have any snce I'm running a different ECU. If I can get some time tonight I'll look and see if I can find the page in the FSM that has the diagram. Quote Link to comment Share on other sites More sharing options...
Jersey Posted September 22, 2003 Author Share Posted September 22, 2003 Thanks Cody. I'm just real curious as to what this things purpose is. It's the valve that looks to be tapped into the 4th intake runner and when removed, it looks and operates like a PCV. When it opens, it allows air into the intake. Quote Link to comment Share on other sites More sharing options...
VinhZXT Posted September 22, 2003 Share Posted September 22, 2003 Jersey, You had it right. Without this valve your car won't idle and will not run. I learn it the hard way. In the process of cleaning up my engine compartment I removed this valve and the car wouldn't run. This valve serves 2 purposes. 1 is to allow just enough air into the intake when the throttle closes to keep the car idles. 2. like a BOV. when you build boost and the throttle closes, on the intake side will create some vacuum and sucks this valve open. Therefore venting the boost back into the intake.. Vinh Vu http://vvu.tripod.com/myz.html Quote Link to comment Share on other sites More sharing options...
Jersey Posted September 22, 2003 Author Share Posted September 22, 2003 Thanks for the reply vinh. I did some tesing myself this afternoon and found the VCV seals at idle (on my Z anyway) and also at any incease in intake pressure, but when you snap the throttle plate closed, it opens just slightly to allow a little air in then closes back up again, doing its job and controlling pressure i guess. I also checked the little 3/4" nipple off the J-pipe on my cousins '83zxt that is connected to this T of vacuum lines and, when you get the T3 spinning and snap the throttle plate closed, it vents hard out of the nipple and must force the air down through the VCV, basically like a blowoff valve as you mentioned, just vents it into the intake instead of the boot before the T3. I wonder what pressure this thing is suppose to start venting at? No real way to test it since there's no technical data about it in the FSM. Figure if it was fatigued and the spring was weakend over the years, it would take less vacuum to open it and could be the cause of slight problems such as high idle since air from the J-pipe would be sucked right into the intake, bypassing the throttle body. Thanks again for reply. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted September 22, 2003 Share Posted September 22, 2003 When I wired in my '82 turbo stuff initially I kept all that crap, and it ran fine. On the second revision, I ripped it all out, keeping the turbo manifold and all the valves on it, teed off. The third revision I replaced the manifold with an N42, no EGR, and the big throat Weber TB. In no case did I ever have any idling or driveability issues. The original stuff automaticaly controlled the idle and after I ripped all the vacuum valves out, I just set the stop on the stock throttle body to adjust idle, and now the Weber has an air bypass to adjust the idle. Not sure I understand the push to make it work. Quote Link to comment Share on other sites More sharing options...
Jersey Posted September 23, 2003 Author Share Posted September 23, 2003 no push to make it work Nathen, i just like to know how everythign works under my hood. That's it. I've had a few and cannot type much more. Sorry. Appreciate the re[ly. Post more tomorrow. Quote Link to comment Share on other sites More sharing options...
john kosmatka Posted August 31, 2004 Share Posted August 31, 2004 So If Im running an n42 intake shaved with no egr valve do I need the vcm valve, Ill also be running a 240sx t-body. Thanks John Quote Link to comment Share on other sites More sharing options...
Jersey Posted August 31, 2004 Author Share Posted August 31, 2004 You should be fine john. The N42 doesn't have the port for the VCV. I can't say for sure how high your vacuum is going to be say, when lifting off the throttle in gear at a high rpm because i would think without any sort of vent (ie. PCV) it would be rather high, but i'm just guessing here. Why no PCV? Just curious. EDIT: Sorry John. Just re-read your post and you said no EGR, not PCV. You'll be fine. Quote Link to comment Share on other sites More sharing options...
Guest 2slo4u Posted August 31, 2004 Share Posted August 31, 2004 I think I remember someone here talking about that valve (vcv) in an older post. Something about allowing the boost on turbocharged models to bypass the throttle plate a little when you let off abruptly so the air wouldn't hammer the compressor side of the turbine. 81zxturbo 95slobaru Quote Link to comment Share on other sites More sharing options...
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