Vacuum and DV question
Site Moderator/B5 Tech Guru
Joined: Feb 2010
Posts: 1,745
From: Bay Area, CA
LM0812, I agree with you that it's much better to run with it - my only point was that it'd likely be ok for a bit without it. You're definitely right that it's better to run with it.
I'm not familiar with those boxes eitherbut as stated above, tapping into any vacuum line at the manifold will give the proper pressure reference for it to work right.
I'm not familiar with those boxes eitherbut as stated above, tapping into any vacuum line at the manifold will give the proper pressure reference for it to work right.
Actually its a ndbw(AEB) vs DBW(2000+) thing. Most DBW owners end up bypassing that valve and running the line directly from the front of the IM to the DV like it is on the AEB. The valve under the IM allows the ECU to open the DV as a safety feature to control over boosting.
On the DBW cars another thing that the ecu can do to cause erratic/lower boost is to close the throttle body and this is also done to control boost/power.
On the DBW cars another thing that the ecu can do to cause erratic/lower boost is to close the throttle body and this is also done to control boost/power.
Last edited by BaseDrifter; Nov 25, 2010 at 02:59 PM.
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2nd Gear
Joined: Jul 2009
Posts: 794
From: Lancaster, CA
So, If I've got this straight, the n249 valve is that little box and that allows the ecu to control the DV. So, by running a line directly from the IM to the DV, the DV will still function without help from the ecu. The wire connection that goes to the n249 must be telling the ecu that there is no vacuum right now, so that must be how it cuts off the n75 and makes the WG only let 5 psi. run through instead of the stock 8 psi.? I hope I got that right lol. So for now I'll just take the line from the DV to the n249 and connect it to the IM and put some vacuum caps on the n249. I wonder if I would pass a CA smog check with it like that.
Thanks for all the replies. You guys really helped me out.
Thanks for all the replies. You guys really helped me out.
So, If I've got this straight, the n249 valve is that little box and that allows the ecu to control the DV. So, by running a line directly from the IM to the DV, the DV will still function without help from the ecu. The wire connection that goes to the n249 must be telling the ecu that there is no vacuum right now, so that must be how it cuts off the n75 and makes the WG only let 5 psi. run through instead of the stock 8 psi.? I hope I got that right lol. So for now I'll just take the line from the DV to the n249 and connect it to the IM and put some vacuum caps on the n249. I wonder if I would pass a CA smog check with it like that.
Thanks for all the replies. You guys really helped me out.
Thanks for all the replies. You guys really helped me out.
Thread Starter
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2nd Gear
Joined: Jul 2009
Posts: 794
From: Lancaster, CA
Just when I thought I had this vacuum line business all figured out, the damn car got me confused again...
Today I tried what you guys suggested, by running the line from the IM straight to the DV. Well, I don't know what's happening now to be honest. My boost increased dramatically, which gave me another misfire in the same #2 cyl. The boost doesn't seem to be erratic like before though. Does this mean the n75 is working?? Also, how did this all change just because I ran a line to the DV and bypassed the n249?? Well, I guess I'll just go get a new coil pack first and see what happens after that. I'm just paranoid about the EPC kicking in like before. Any insight is appreciated. Thanks.
Today I tried what you guys suggested, by running the line from the IM straight to the DV. Well, I don't know what's happening now to be honest. My boost increased dramatically, which gave me another misfire in the same #2 cyl. The boost doesn't seem to be erratic like before though. Does this mean the n75 is working?? Also, how did this all change just because I ran a line to the DV and bypassed the n249?? Well, I guess I'll just go get a new coil pack first and see what happens after that. I'm just paranoid about the EPC kicking in like before. Any insight is appreciated. Thanks.
Site Moderator/B5 Tech Guru
Joined: Feb 2010
Posts: 1,745
From: Bay Area, CA
Just when I thought I had this vacuum line business all figured out, the damn car got me confused again...
Today I tried what you guys suggested, by running the line from the IM straight to the DV. Well, I don't know what's happening now to be honest. My boost increased dramatically, which gave me another misfire in the same #2 cyl. The boost doesn't seem to be erratic like before though. Does this mean the n75 is working?? Also, how did this all change just because I ran a line to the DV and bypassed the n249?? Well, I guess I'll just go get a new coil pack first and see what happens after that. I'm just paranoid about the EPC kicking in like before. Any insight is appreciated. Thanks.
Today I tried what you guys suggested, by running the line from the IM straight to the DV. Well, I don't know what's happening now to be honest. My boost increased dramatically, which gave me another misfire in the same #2 cyl. The boost doesn't seem to be erratic like before though. Does this mean the n75 is working?? Also, how did this all change just because I ran a line to the DV and bypassed the n249?? Well, I guess I'll just go get a new coil pack first and see what happens after that. I'm just paranoid about the EPC kicking in like before. Any insight is appreciated. Thanks.
Doesn't sound like a bad thing. Get that misfire taken care of and see how it runs.
Last edited by BaseDrifter; Nov 30, 2010 at 12:32 AM.
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2nd Gear
Joined: Jul 2009
Posts: 794
From: Lancaster, CA
Yeah, I'm crossing my fingers that it's a good thing and no, I don't have a boost gauge. I was thinking about just getting a cheap one from Pep Boys or Ebay so I can at least see what the hell's going on with my boost levels. The coil pack is first though like you suggested.
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