Unknown sending unit
 

I have this sending unit just below the intercooler. Nothing is connected to it and there are no wires nearby. Any thoughts?http://forums.pelicanparts.com/uploa...1345084263.jpg

Overboost sensor, bet you have a white wire grounded someplace....(edit, it's right next to it grounded on the bolt)
I would hook it up, shuts off the fuel pumps over 1.2 boost to protect the engine.

the brown wire to the left of the sensor and slightly up is what he is referring to. yeah pretty important

The brown wire in the photo is already attached to some type of sensor. Is that one normal?

It is actually a white wire and it gives earth to the fuel pump relais. If mounted like this, pumps will stay running on too high boost. Switch is cutting-off at 1.3bar, which makes sense. So just put the connector on the switch for safety

Your overboost wire has been moved to a grounding tab purposely. I'll bet if you move it back to the overboost sensor you'll get the teeth in windshield experience.
Is the engine running a 1bar spring? Short tube headers? If so the overboost spikes experienced in the BOV can trigger the sensor.

I am in the process of un-grounding this same wire and connecting it back to the same sensor, as my PO did the same thing: permanently grounded the wire referred to above. I'm interested in your comment about "teeth in the windshield". Does that mean that when the sensor is activated - i.e. during overboost, and the pumps cut out, it is not a "gradual" cut back of power, but a full stop of the engine? Will the engine literally stall/stop or just go back to a non-boost state?

And a related question: I assume the PO did this because he had installed a non-stock spring and didn't like the pesky Porsche design ruining his fun on overboost. Question is, what is the best/easiest way to know what spring/boost the engine is running? The standard boost gauge only goes to 1 bar.

I know this is simple stuff, but thanks for your patience with a newbie 930.

Yep, it stops immediately. Very abrupt. When people ground the wire to the sensor, it's usually because the sensor has become faulty and tripping too soon under normal boost conditions, or because it's failed completely and is in a permanently open circuit which prevents the pumps from running.
If you doubt your boost level (don't trust the in-dash gauge) then install an aftermarket remote gauge of known accuracy to check. Are you running with the stock Porsche wastegate, or with a Tial? The Tial has color coded springs to identify the boost level it controls to.

Those overboost sending units are total garbage.
They are so poorly made and overpriced it's ridiculous. I bought a new one from pelican years ago for $60 and it goes off ruining the driving experience every time I floor it but I run 1.2 bar with more than enough fuel, WMI, and I can retard ignition timeing and adjust boost from inside the car while driving.

If yours abruptly and dangerously shuts off the fuel pumps when floor you it while that wire is on the sending unit you can replace it with an adjustable hobbs pressure switch.
They are MUCH higher quality construction, cost half what the piece of sh.. german one cost, and you can adjust what pressure level it triggers and disconnects that wire from ground.

Wayyy better soloution in all respects and it lets you be in control again.

https://www.google.com/#hl=en&sclient=psy-ab&q=hobbs+pressure+switch&oq=hobbs&gs_l=hp.1.2.0l 4.0.0.1.451.0.0.0.0.0.0.0.0..0.0.les%3B..0.0...1c. D0Msysw89-0&pbx=1&bav=on.2,or.r_gc.r_pw.r_qf.&fp=3c711fb061a c048&biw=1920&bih=952

No idea what spring is in it.

I know there is a new K27 S Turbo and a fresh top end rebuild and not a great deal more.
It is starting to sound like I should leave it be

Thanks for the reply regarding the overboost switch/behavior. Leaving it grounded is the simple solution, but if I understand what my mechanic has been teaching me, the risk is that (assuming a non-standard spring) the car will run at higher-than-design boost, which, unless other mods are made to ensure sufficient fuel and charge cooling, can result in engine damage due to lean/hot conditions on boost. Assuming that is a correct concern, then what I don't know is whether it is a "long-term" issue, that is, not a problem for "occasional" overboost, or whether it is playing a losing game to overboost when I don't know about whether other mods are in place to handle the additional boost. Is that a fair summary, and if so, wouldn't it be safer to reconnect the switch and avoid overboost?

I think my wastegate is stock, although I'm not sure. If it were stock, does that mean that the spring MUST be stock, or can people put a non-stock spring into an OEM wastegate?

Thanks again...

Common to put a 1 bar spring in a stock wg. I'd be surprised if yours didn't have a 1 bar at least. If it pegs to 1.0 on the boost gauge it probably has one.
There is no downside in my mind to hooking it up.

Hook it up, Manitop. It's your insurance. If you're running more than stock boost, it puts you closer to the edge where boost spikes could stress the engine. Let this safety devise shut her down for you if/when that happens. Plus, it would also protect you in the event that a simple rubber hose failure can cause if your boost signal hose to the WG were to come loose, or the diaphram within the WG should tear incapacitating your boost control.

Thank you Mark & Tt, sounds like good advice to me. Gauge definitely pins, and motor is currently undergoing surgery to fix (among other things) broken rings. Sounds like the PO had too much fun with a 1+ bar spring and I'm paying the piper.

Next step in my education is to figure out how to make use of 1+ bar the "right" way; with proper mods, which, I believe, include enhanced fuel supply, larger intercooler, and ? But that is another thread....

Best,