Theta

Alright, now it's time for me to pick your brains about something.

Required info: I have two Innovate digital gauges: the MTX-L for AFR, and the MTX-D for Boost/Vacuum.

The lines are setup in the following way (see pic) per the PCV "fix" of separating the valley cover and intake manifold barbs.



As you can see, I have the T-line running from the intake manifold bard to both the gauge and the blow-off valve. This operates the valve without any issue, but the gauge will only show vacuum. When going into boost, it simply registers 0.

Here's my thought here... the manifold tap is only ever going to show vacuum since it's been separated. So... anyone have a recommendation for showing both boost and vac, or perhaps even simpler, does anyone know a good place to grab boost from?

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So... Any ideas?
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Matt @ FSP

The valley port will not show proper boost , that is only the pressure in the crankcase itself.

Theta

Hmm... Okay, blows that idea. It was a little complicated for my own liking anyway with three Tees, two check valves, etc.

Matt @ FSP

Technically, pressure ("boost") is in the intake manifold during positive pressure operation, so the hose from intake manifold should show boost unless there is a check valve on the intake manifold side. If that is the case it does not see boost on that side but I doubt that there is one in the int side...

Theta

Just replied to you - no check valve in the intake manifold for sure.

Stumped...

Theta

Oh, and in case anyone is wondering, yes the gauge works fine.

Gadfly

So the gauge is T'd into a vac line that runs from the intake manifold to the bov?

That is a correct install, and should show you manifold pressure both in boost and in vacuum... so either the line that runs to the gauge is pinched off somewhere, or there is a check valve preventing boost from registering.

Does the BOV work correctly? If there is no positive pressure making it to the top port on the BOV it will blow open while is boost.

Theta

Precisely - T running from intake manifold to BOV and gauge.

Vac tube to sensor is straight , un-pinched, and the sensor is sitting right next to washer fluid spout on the driver's side engine bay.

I've already done the hillbilly test - took the hose off, blew and sucked - gauge registered boost and vac values (small though they were).

I'm concerned that perhaps the wildly-loud BOV noise I was hearing today has something to do with this... Theoretically, if the valve never closed, I'd still be making boost at a greater rate than it could escape through the BOV...

Might be time to break out a mechanical gauge.

Theta

Okay, basic tests completed...

1) Gauge is fine, used mechanical to verify side-by-side.
2) No check valve on the intake manifold port - free air back and forth...
3) No leak on the BOV when off - spring is holding it tightly.

Bad news...

After reviewing the videos, it sounds like the BOV is never closing... Actually positive of it...

So that means there's no boost pressure running through the intake manifold... What... The... F...

Can somebody else with a blower or another shop take a wild-*** guess at this?

Things learned:
a) A human male can exert 2.1psi of pressure through a small air hose, and create 12in/hg of vacuum...
b) Crankcase gases are bad, mm'kay?

What a night...

Video mentioned above - listen for the boost - BOV isn't closing (try starting at 27 seconds):



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runutzzzzz

Something isn't right. You are grabbing from the correct location. Do you have another gauge to test it with?

NSC5

Well, from your install thread the performance gain seems to indicate you are getting significant boost. I would start by pulling the line at the manifold tap and apply pressure to the line to see if you have a leak at the BOV control or somewhere in your line or the T you used. That small line cannot flow very much air so a leak would drop line pressure without materially affecting overall boost.

It would be a true oddball case but a defect/cut in the line could seal under vacuum but open under positive pressure creating the odd reading you are seeing.

Z_Rocks

Which BOV is this? And what spring pressure does it have?
Way back when I had my first Centri on Corvette, as I would drive in 2nd gear with throttle partially open, I could hear exactly the same sound as yours where all the boost was rushing out. This was because of the cheap BOV that came with the package. I then bought the TiAL and them install it on a new pipe and solved the problem.
I think the one I bought was like this with 11lb spring.
http://www.rallysportdirect.com/Tial...FchQ7AodfDMAuw
Check out the different springs in that page.

In the video, I could hear the sound started as you stepped on the gas with the throttle open (which means the spring in BOV is not resisting the pressure) as opposed to when the throttle is closed (that's when the spring should let the pressure out).

I bet the BOV isn't working right.

Plexoer

Don't mean to change the subject, but Theta you don't happen to live out in O'Fallon do you? I think I may have seen you out there.

slief

His BOV is a Tial as per his Unboxing and install thread. Here are a couple pictures of it from that thread.

OD3G

In the above picture both sealing washers are on top of the fitting when one should be on each side. Could very likely have a boost leak at that fitting which is causing no boost to read on the gauge.

Theta

Bloody hell, that might have just done it. Will check when I get home from the hospital.

Theta

Maybe.... Depends on what you saw me doing.

Did it sound good?

Z_Rocks

Thanks, I had not followed the thread completely.

Exactly!

Skunkworks

Most bypass valves are setup to close at near atmospheric pressure, when you are idling or revving engine without load you still have too much vacuum (likely what’s going based on your video).

With engine not running bypass valve should be closed. When running at idle it should be open. If both statements are true, then don’t worry about it till you can drive it. When on the road roll into throttle at ~3000RPM, you should be able to feel it close.

The bypass valve is designed to keep impeller out of surge margin - surge is a localized or full rotating stall followed by flow reversal. Or more simplified the impeller is trying to flow more than engine (downstream flow) will accept. This happens during shifts (if stick), hard deceleration or high RPM and low throttle opening…

Theta

Sorry guys, my mind has been elsewhere. I should have mentioned this was observed during my drive yesterday.

Video was an example.

I will try the seal fix and see if that's the issue seems very logical.

Sorry, only have a phone at the moment.