Boost gauge, pressure sensor, & rapid clicking under hood
 

Okay, just got my '90 TurboII running. One problem I'm having now though is..

When I was driving it, I noticed that the boost seemed to be spooling fine, but the boost gauge wasn't showing much (if anything) above 0. When not running, it would sit at -20. Then when I put it to the on position, it goes up to 0 and sits there. When I'm driving, it stays at the same place, and doesn't really seem to move.

I'm pretty sure there IS boost, it don't feel like a 130hp car, and I can hear the whine as the RPM goes up.

So, I pulled the electrical connector to the pressure sensor, and turned the ignition to on. It stayed at -20. I plugged it in and a clicking sound started coming from somewhere in the engine, I can't tell where. Really rapid clicking too.

So I turn it off, unplug it, turn it back on, back at -20 and no clicking. Turn it off, plug it in, turn it to on, and it starts clicking again.

So who can solve the problem?

actually just drove it again, the clicking went away after it sat off for a while.

When I brought it up to "on", it stayed below 0, but a little above where it sits when it's off, a little above -20. Then I turned it on, I think it moved a little.. Bring it out, run it up to about 5500 in 1st, 5000 in 2nd (it's been higher, but now I don't want to bring it too high while the pressure sensor might be messed up, I don't want to blow it). Anyhow, brought it up to those 2 listed RPM numbers, and it moved up a little bit more, still not above 0, but this time it stayed there and didn't go back down below to what it was at before. I'm thinking maybe it's sticking? I don't know?

oh yeah, one more thing.. just to make sure I'm not a complete idiot, the fairly little vacuum line that's on top of the BOV (that IS the BOV isn't it?) is the one that goes to the pressure sensor, right?

YOU BLOODY IDIOT! joke. No. The intake manifold has two nipples dedicated to each item. One for the bov and the other for the pressure sensor.

I only have a 87 and have never touched a 90 whatever. But I'm sure the setup is the same. One nipple should be on the acv. Its the one pointing straight out towards you. Just a few inches to the rear of that one, is another for the bov. Right now I forget the real name is for what we're calling the bov.

you sure that's right for the '90? I'll go out now and look at it, see if that's the case, but I didn't see any open lines, and the sensor lines I THOUGHT were shorter than that. I'll doublecheck again though.

I just checked the lower intake manifold. It SEEMS that there's 2 little nipples on the forward half of the intake manifold, BUT they're going to this little metal pipe thing, there's 3 little "vacuum line" like thingeys.. two of 'em are connected to the intake manifold, the 3rd I forget what it's connected to.. anyone identify these? The manifold is an A-spec, the engine is a J-spec.

Hailers is right (as usual!) about those nipples. There's one on the manifold for the BOV and one on the ACV for the pressure sensor. This is for S4 and S5.
You need to get an aftermarket gauge on there. The stock one is pretty much useless for taking accurate readings anyway, but you need another gauge to confirm whether the sensor or gauge is at fault or if you are indeed running low boost. If the sensor is broken you need to replace it ASAP because it's very important for keeping your engine together at high boost.
From your description above though the gauge sounds OK. It should be at zero with the ingition on and the engine off, and at -200mmHg at idle. The manifold pressure at idle is actually well below that (380-400mmHg), which is why the gauge doesn't move until you use a bit more right foot to get manifold pressure above -200mmHg (another reason the stock gauge is no good). If if goes straight to up to zero when you floor it but not much higher, you may have a boost problem (hose leak, tired turbo).
Get that gauge first, it's vital for troubleshooting. :)

yeah I want to get an aftermarket gauge, but I don't really have the $$ to do that yet. I don't really run it more than stock or tune it myself, so stock is sufficient for now.

But anyhow, so I can disconnect 2 of the lines from the 3-part metal vacuum line thing? Then reconnect them towards the pressure sensor and the bov?

anyone know if this is ok, or what these things go to?

I know the feeling... You really need to confirm what your boost is though. A dodgy pressure sensor could be an engine killer, and low boost indicates other probs. See if you can borrow a diagnostic pressure gauge from a mechanic. No! Leave those three lines on the vac spider alone, they're nothing to do with this. Have a look at this pic of my manifold with the ACV removed. You can see those three lines capped, and the line for the BOV going to the manifold. The pressure sensor line normally comes off the ACV, but you can see mine's tapped into the BOV line. The nipple for pressure sensor on the AVC is the one up the top that points outwards (not upwards).

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