Quick Question- No vacuum readout on Boost Gauge?

Hi all, just a quick question here.. I've been running my new manual boost controller along with a gauge for about a week now, its set at about 11 Psi (No higher until I get new spark plugs), all seems to be working well and fine. Only thing that has kinda bothered me is that I have never seen my gauge show vacuum, mind you-- yes it is a boost/vac gauge not just a boost one, but it is my understanding that after a shift the gauge should drop down momentarily to a vaccum as the extra boost is released by the BOV. Under medium acceleration the boost does drop after a shift ... to between 0-2 Psi, but I have never seen it go into a vacuum. Should this only occur on a truely hard shift at high Psi, or is this a possible indication that my BOV is not working properly or has a boost leak? I am confident that my gauge is installed properly etc and is air-tight, but should I be concerned about this at all?
Thanks.

where do you have it reading the boost/vac from?

where do you have it reading the boost/vac from?


yea, make sure you have your boost gauge connected in after the throttle body

From this thread
http://www.automotiveforums.com/vbulletin/showthread.php?t=691878

second note, is it just a boost gauge? or is it a boost / vac gauge?

If its a boost / vac gauge it needs to be hooked up to a vac line that comes off the upper plenum / intake manifold after the throttle body or you will never read vac correctly.

Bah! I should read more carefully... my boost gauge was tapped before the throttle body at the y-pipe.... when it should have been from the plenum. Well I've switched it once again and am about to test it all out to make sure all is going fine.

nice man that should help! haha goog luck!

Ahhh!! Despair continues.... now that my gauge is tapped into the Plenum Line, I'm only reading vacuum, no boost shows up at all when driving. Let me check if this is right... at idle it reads at about -15Hg, when accelerating lightly to medium around town I am staying in vacuum, the closest to boost I got was around 0 Psi... I am going to upload pics of the install in a minute as I am certain I have something hooked up incorrectly.

here we go:
http://img407.imageshack.us/img407/6545/0417071941adi5.jpg
http://img405.imageshack.us/img405/1381/0417071942zj4.jpg

As you can tell I dont have the gauge directly from the plenum, I split it off from that hose distributer...which I am uncertain if I even need... just left it there to be safe..

Before I was reading boost basically between the Y-pipe and MBC.. which seemed to work fine...
Maybe I am leaking boost with the new setup?

Ok, I located a leak coming from the other side of the vacuum hose that ran out of the plenum through the distributer and a ways down out of that to what I believe is the fuel pressure regulater...in short I replaced that hose so now its pressurized. Anyways,I do seem to be reading boost now though it doesnt seem to be much.... is a -16Hg normal for idle... and is a -10 to -5 normal for cruising? I did get it to go up into positive but even with heavy acceleration I dont think I really went higher than 6 Psi.... something just doesn't feel right. And I haven't touched my MBC, it still shows around 4 threads which previously the gauge read at around a max of 11Psi from the y-pipe.

Also I can definitely see the gauge drop to about -15 whever I put the clutch in. Should I just run a straight vac line coming out of the plenum T to the fuel pressure regulator? I've read the vacuum reduction mod but its left me somewhat confused... nonetheless my setup does look similar to this, 2nd picture:
http://www.3si.org/forum/attachment.php?attachmentid=59639

you still have a leak somewhere

at idle, you should be sitting at -20, if your driving, then let off the gas, you should drop below -20 and then come back up to -20. If your having trouble building boost, you probably still have a boost leak somewhere. Where you tapped the line in does look correct.

Okay, I'll take a look once again tomorrow. In terms of minimizing the number of vacuum hoses, as in the reduction mod, is it safe to remove the entire metal bracket that sits on the throttle body and connects to the adaptors on the firewall, so long as I make sure the one line from the plenum goes to the fuel pressure regulator, or are there other lines that I would have to cap or run if I wanted to eliminate that?

Full guide is here http://www.3si.org/wiki/index.php/Vacuum_Reduction
Looking at that I dont want to entirely replace all my hoses, but I'd like to eliminate the bracket I was just talking about.

Thanks again.

normally what i do on a vacuum reduction is I pull all the solenoids, all the vacuum hoses in the area, the bracket on the throttle body and the long hard lines that run from the rear to the front of the engine bay. I then cap off the 3 nipples on top of the throttle body, run the nipple from the back of the intake plenum to the boost gauge, run the nipple on the back of the y-pipe to the inlet of the boost controller, run the outlet of the of the boost controller into a vacuum T and run those to the wastegates. Then I run a hose from the fuel pressure regulator to the nipple on the intake plenum thats located near the front side of the throttle body, then cut that hose somewhere in the middle, insert another vacuum T and run that to the blow off valve. Then I make sure that all EGR crap is pulled off and install EGR block offs. Thats it. However, those steps will be modified according to the emissions you have or what you are wanting to do. My steps get rid of everything.

Alright, after re-doing much of my vacuum line, I've finally located the cause of the leak itself... the back back of my stewart warner boost gauge actually. It turns out that the installation kit was supposed to include some type of ferrule for securing the tube lining air-tight to the back of the gauge.. unfortunately it did not come with such a device. I just tried tightening it and using a rubber barrier to create an air-tight fit, which did not work. So I just decided to glue the base of the fitting to the adapter with some PVC glue..now waiting for it to dry to see if that makes it airtight.

I've re done almost every single vacuum hose. The back of my gauge is now completely secure and airtight. Yet still I start up my car and idle at -16Hg. How can I still have a leak somewhere? I have check everywhere, the only other thing that comes to mind is I read somewhere that a screw on the throttle body can cause a leak as the rubber wears off....yet I have no idea which screw this is/ what they are talking about. I know where the idle RPM screw is, but I know that isn't where the leak is...

This is driving me crazy as I have been spending fay after day re-doing stuff and looking for leaks, my gauge installation is turning into a 2 week nightmare.

I Havent been staying up to date with your luck.. but have you tryed putting it on the same line as your BOV? if not try that just for kicks

Easiest way to find leaks is to pressure test. Do a search, make a pressure tester, and pressure test. Easier to find leaks when you don't have to listen over the engine idling. Plus it will find leaks under boost that maynot be audible under vacuum. Chances are, if you havn't pressure tested before, you have quite a few, not just one or 2. The rear turbo/IC pipes' rubber gaskets, plenum gasket, biss screw's rubber O-ring, etc are some of the more common ones.

Well either way I'm definitely leaking somewhere... as I cant build Psi. I'll probably have my friend come over tomorrow, he knows much much more about cars than I do, and I've seen the guide for building a pressure tester, I may have to do that as well.

I'll make my way over this weekend and well give her a pressure test...hopefully locate all the leaks and seal them.

Just to make sure. When you are trying to build pressure...are you driving hte car, or are you just reving it in the driveway. Because you aren't going to build noticeable boost while the car is sitting still.

Either way there seems to be a vacuum problem due to the fact that when in idle its only giving a readout of about -16 when it should be -20...I'll drive it around before I do anything to it tomorrow to kinda get a ballpark of the numbers its getting.

Undoubtedly it has leaks...that accounts for the vacuum discrepancy. If it hasn't been pressure tested recently, of course it will have leaks. But not being able to build ANY boost pressure at all, makes me wonder if he's trying to build boost with load on the engine, or if he's just reving it up in his driveway...hence why I asked.

Ahh, I'm not sure if I said it before but its not that it wont build up boost at all, its more like the max boost I can reach is around 5 Psi, which was driving around under heavy acceleration, so yeah its definitely leaking. Anyways after a bit of testing it sounds like the leak is coming from the rear turbo, so tomorrow we're probably going to jack the car so we can get a better look at it, its probably the line or seal on it.... we shall see. Also planning to replace the o-rings on the throttle body, I'm sure those are worn to hell.

... if you have a boost leak.. lifting the car is not going to help you find the problem if its your rear turbo

You sure you hooked it to the wastegates properly...sounds like you are just running wastegate pressure.

Also make sure you have the mbc set up the right way. And not the inlet/outlets reversed.

Lastly, have you started slowly tightening the mbc a 1/4 turn each time and building your way up? Because if hte screw is loose, all you will see is wastegate pressure.

Boosting at wastegate pressure, usually isn't a bunch of minor boost leaks...generally it's something done wrong.

It isn't my connections at all, I have replaced every single piece of vacuum hose in the car and completely finished the vacuum reduction mod. My hose diagram looks identical to the digram I posted earlier from the guide. Only thing I have left to do is the o-rings in the TB, nonetheless I am still idling at -16 and car hear a sucking/leaking sounds coming from around the upper plenum/TB when the engine is running.

http://www.3si.org/wiki/index.php/ThrottleBody_O-Ring_Replacement

Is this the guide I should be using to go about replacing the O-rings in the throttle body? Because it just seems a bit overly complex and it looks like it would be easy to mess up. Is there any other way to seal the TB for leaks? Or should I just try and go about as directed in the guide? I remember something about the idle screw o-ring, is that what the guide ends up replacing?