Boost guage reading vac. searched
 

I know this is a stupid ? but I am new to turbos. Simply put I have connected the line from my aftermarket boost guage to evry nipple on the car to determ what one works. Where I thought and then searching reveld same awnser was T it into the PS line. SonicRat said use a nipple on the TB or behinde it basicly after the flapper doors. So I tryd the 3 nipples right behinde the TB towrds front of car. My line for the PS runs like UIM - T--BOV - more line T -- boost guage -check valve - PS
All emishions are removed from engin. Ither way the guage only reads VAC 18inhg at idle and neer 30 at higher reves.

T off of the stock boost sensor.
-John

you can you use the bottom nipple on either the back or the front of the UIM. I have mine connected to the rear one...

Ill try that martin thx. where is the stock BS?

Actually it's a pressure sensor on turbo and a boost sensor on an NA IIRC. Anyways it's on the passenger side strut tower.

As I posted I T'd into this line and I only get VAC readings. My BOV is T'd here as well.

Unless I totaly have this whol section routed to the wrong nipple.

I'm confused by your first post. Where is your vac source for the pressure sensor and anything else you have tee'd off it. The 3 nipples on the front of the UIM (near the TB) do not all read vac and boost. Only the top and bottom of the 3 in the front read vac and boost. The middle is only vac I believe.

Someting is wack with my car then. I hooked the boost guage only to the top nipple of the 3 next to the TB and my guage only reads VAC.

I have the PS and BOV T'd coming from the single nipple in the middle right next to the BAC and above the ACV. I allso hooked my boost guage with a T here as well and got VAC only.

So you actually drove your car under load to test that it will not read pressure? Or are you checking this at idle?

I am reving the car under no load. My BOV goes off strong.

Not everyone can build boost at idle. Some can. Drive the car and I bet you will see positive pressure unless your gauge is broke.

Well I figured if BOV is going off when reved its building boost. When I rev it the guage dives into VAC. Guage works I used a VAC/boost presure tester on it. I will drive it and see when car is driveable

Like I said before, I like to runt he pressure sensor/bov off the nipple on the UIM near the passanger side of the car, near where the BAC is. For gauges, I generally use those on the TB. Most of the time you won't be able to build boost just revving in neutral so this could probably explain why you never see it. Just because the blow-off valve sounds doesn't mean it's building boost.

Ahh thx u for the clear up!

Actually it's a manifold absolute pressure (MAP) sensor no matter what engine it's on. They both do the same thing and both work the same way, so they do not have different names no matter what Mazda says in the FSM. The parts manual actually calls them both boost sensors.

The only difference between NA and TII MAP sensors is how high they read up to. The TII sensor goes up to around 15psig positive pressure (30psi absolute) and I believe the NA sensor reads up to 2-3psig (17-19psi absolute), which makes it a pretty crappy "boost" sensor. ;)

Some BOV's don't even need a load to sound off.

Usefull nfo NZ thx.
Rexryder realy. I thought boost had to be built up into the piping atleast the TB plates to sound off when there snaped shut.