Boost Leak From BOV Dump.

[mcarruthers]

Hey guys, this is my first post, bear with me. I've searched the forums and haven't recieved the answer im looking for. I recently purchased a 92 talon tsi. It came with an UICP and atmospheric BOV (no name) (unproper set-up). The car will hit 9-10psi. It pulls hard at about 5psi, but above that seems slugish. Boost leak for sure. Ive BLT'ed from the hose which connects to the J-pipe to the intercooler outlet, and that's holding well. No if I go one pipe farther (caping it before the throttle body) it builds 0 boost, in a test. All the air rushes from the BOV dump. I have a factory upper pipe and BOV (crushed), and installed it to compare. It will build boost during the test to about 10-11psi but will not hold above 5-6psi. Again all the air is dumping from bov dump. ***My question, are these BOV's leaking due to un proper BLT or malfunctioning BOV? When doing a boost leak test from the J-pipe hose to end of the upper intercooler pipe, should it retain boost, or does the BOV need boost from small vacuum line to keep valve sealed?
Thanks for your time, Matt

 

[dsm_Crazed]

You have the vacuum line from the intake manifold to the BOV hooked up, right? You can't properly test that pipe unless you have that pressurized air making it to the intake manifold. Spring pressure keeps that BOV closed normally. That vacuum line from the intake manifold allows the boost pressure to go to the top of the diaphragm in the BOV, and help keep the valve closed with boost in the pipe. This way, you have:

spring pressure + boost > boost

If you have the pipe capped before the throttle body, then there is nothing but that spring pressure holding it closed, and its naturally going to open when boost gets higher than the spring pressure.

 

[mcarruthers]

When I do a full system test theres to many leaks to build any boost at all, so I wanted to do it piece by piece, to isolate the problem. Thanks for the info, thats kind of what I figured. I just wanted a second opinion. I appreciate it.