Need help with boost guage
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Teching In
Joined: Aug 2002
Posts: 3
Likes: 0
From: NW Fla.
Need help with boost guage OK, got the ATI put in. Went in pretty easily. Now, the only problem I am having is the boost guage isn't working. At first I thought it was the guage, but it isn't. Here's the deal. It's spliced into the brake booster vacuum line as per ATI's instructions. My understanding is that this line is under negative pressure and as boost builds, it goes into positive pressure and this positive pressure is pushed through the line and displayed as boost. Here's the kicker. I removed the nylon line and put my finger over the brass nub where it connects. Sure enough, it was sucking on my finger (negative pressure). Then I had someone give it gas. No matter how high we ran the RPM's up, the line never went into positive pressure (it never blew air out the nub, but continued to suck it in). How is this possible? My understanding of this issue is somewhat limited so bear with me. Anyway, I checked the line to the surge valve and checked the valve itself, and it seems to be in perfect working order. However, since no positive pressure is ever in that line, the surge valve is always open which means it is always venting out that line instead of shutting at boost. The valve works properly. The problem is that I don't have any positive pressure into the line I tapped into. Yes, I did tap the right valve, assuming that ATI doesn't have a misprint in their instructions! LOL!!! Any suggestions all you physics guru's out there? I'm supposed to go for custom tuning Sat. and I need to get this resolved. Thanx in advance guys.
Moderator
Joined: Nov 2001
Posts: 3,048
Likes: 12
From: Raleigh, NC
Re: Need help with boost guage Though the intake is my choice, too, I think others have used the brake booster line as a source to read vacuum and boost.
If the line has vacuum, if the motor is pressurized (boosted), the line must have pressure as well. Someone correct me if I'm wrong. Another questions I would have is does the motor build measureable boost just by rev'ing without the engine being under load. I've never checked that, and it may seem a silly question, but some knowledeageble expert may be able to help us out here.
Perhaps you don't have boost? Tap into the line coming off the left side of the intake and see if you have the same indications.
Good luck!
If the line has vacuum, if the motor is pressurized (boosted), the line must have pressure as well. Someone correct me if I'm wrong. Another questions I would have is does the motor build measureable boost just by rev'ing without the engine being under load. I've never checked that, and it may seem a silly question, but some knowledeageble expert may be able to help us out here.
Perhaps you don't have boost? Tap into the line coming off the left side of the intake and see if you have the same indications.
Good luck!
Launching!
Joined: Feb 2002
Posts: 210
Likes: 0
From: miami
Re: Need help with boost guage Blackls1 is on to something. You should not be reading boost if the engine is not under load. You might get a decrease in vacume but the pressure will not build. The engine is reving to fast and it wont allow presure to build in the manifold. Trying running it down you block in first or second gear You should get a boost reading then.
