Skunkworks

Theta,

You said “It obviously has some amount of boost in order to close that Tial valve”… As mentioned before, bypass valve closes at below atmospheric pressure (some vacuum threshold, depending on spring, adjustment…), or it is engine vacuum that is opening it. If it took boost to close valve (not venting), then how would you get into boost? Yes, undersized bypass valve could do it, but you are not undersized in your application. Don’t get too hung up on this detail, because based on previous video it appears to be actuating just fine.

You have new parts so not suspecting shredded o-rings or similar, but anything is possible. There are many things that could cause issues, but not time for a witch hunt yet.

As others and I mentioned check for leaks if after drive you cannot get into boost. Do your testing at 3000+ RPM.

As far as putting a gauge on that line… As long as it’s a line after throttle body (from intake manifold) that is free flowing, then nothing to be concerned about.

Your mechanical gauge results are normal, the blip you got followed by some oscillation is normal for an un-dampened type. Most electronic gauges have a low pass filtering built in…

Theta

This is one of those times semantics actually comes very much into play. Can't have boost without the closing of the valve (unless as you said the valve was undersized which it's not, etc), so rather it's the transition from vac to boost that's allowing the spring (with a rate equivalent to 2 psi, I believe) to overcome the vacuum. I phrased it wrong.

The good news is that, regardless of whatever the root cause of this gauge oddity turns out to be, the valve is working properly.

Skunkworks

Last post on the valve… As shipped is it closed with engine not running? If yes, then nothing to do with boost, as mentioned it is vacuum that opens it.

From Tial http://tialsport.com/index.php/tial-...ovs/46-tialbvq , you’ll notice that springs are rated “-X PSI” or a negative pressure… It is the “-2 PSI” or more -3, -4.. (when negative value - it is a vacuum) as an example that dictates when it/valve starts opening.

Not trying to be jack azz, but you are looking at it backwards. The vacuum overcomes spring pressure to open valve. Or the valve is normally closed and vacuum is required to open it, lose vacuum and it closes... The point at which it starts opening is dictated by spring pressure, the more spring preload, the more vacuum required to open it.

Theta

I stand corrected - I'm used to solenoid-controlled BPVs in my turbo cars (read: letting something else do all the work without any thought involved).

So essentially I am (or was) looking at it entirely backwards. Same in the middle, but different (opposite) forces acting.

twokrx7

Have you pulled the hose off the mani and then pressured up the host/fittings/etc with a manual hand pump/gage to verify your in-cabin gage readout and confirm no leaks in the boost gage system?

Theta

Yep, everything's good including the readings on the two different gauges.

My working assumption at the moment is that my two gauges (digital and liquid-filled mechanical) are not getting the split-second response - or rather are filtering it - that the cheap pressure tester with the incredibly-bouncy needle is getting.

Since it's only in boost for a fraction of a second, that may just not be enough to 'excite' the other gauges, unlike the cheap one that does show the needle spike.

So, when I put a load on it again today or tomorrow I'll test that theory. Just in case, I ordered another of the same boost gauge in case the sensor was faulty, etc. or wasn't reading quickly enough. Grasping at straws, but it's a possibility now that the mechanical side (hoses, barbs, etc) is 100%.

Theta

Took it out today after all the changes to the BOV bolt/nozzle, new tubing, etc. and had a little better luck with the digital gauge. The instant (but seriously annoying) monitoring of the cheapo mechanical pressure gauge was spot-on.

There does seem to be some sort of lag period that the digital gauge is using before showing boost, as it sits at 0.0 for a good half-second before showing boost now.

So, whatever combo or single item fixed it, I'm just happy it's working correctly now. The BOV sounds quite a bit different now than the last time I drove it (which makes it seem like I had something going on there, as well).

I'm hoping the new sensor with the new gauge will not have that delay, but it could be just how they designed it.

Oh well - wish I knew what it was, but case closed!

carlrx7

why not use a vacuum manifold off the brake booster line?

BrunoTheMellow

Sorry to revive an old thread but did you ever do a How-To on this Theta? I know several people wanted to see it. Would you mind taking a few pictures of the wiring/connections. I understand the PCV tubing stuff now but everything else is greek to me.