lenat

In summary what I have verified:
1. Serpentine belt moves
2. Engine aka timing belt moves ( I haven't verified timing as car is not in the place where I could removed belt cover, which means bumper removal)
3. Intake and exhaust cams are moving
4. Measured compression in cylinders, about 30 psi
(of course ign. coils ar ok, spars are ok, fuel pump is ok, fuel pressure is there)

I haven't yet tried to put a tablespoon of oil through spark plug holes. Do you recommend doing it or is it already obvious that I need to take the cylinder head off and inspect the valves?
What are the reasons to lose compression other than bent valves

What I noticed with valve cover open is that cam chain tensioner isn’t going up. I have understood that it should move up and down?

Back to the beginning where I stated that I wasn't able to get any fault codes with Vag Com nor the engine light came on. So when I removed everything necessary to get the valve cover open, then all disconnected connectors (also fuel pump fuse nr. 28) triggered fault codes, but then again these were triggered by me:
10 Faults Found:
17645 - Fuel Injector for Cylinder 1 (N30): Open Circuit
P1237 - 004 - No Signal/Communication
17647 - Fuel Injector for Cylinder 3 (N32): Open Circuit
P1239 - 004 - No Signal/Communication
17648 - Fuel Injector for Cylinder 4 (N33): Open Circuit
P1240 - 004 - No Signal/Communication
17646 - Fuel Injector for Cylinder 2 (N31): Open Circuit
P1238 - 004 - No Signal/Communication
17833 - EVAP Purge Valve (N80): Short to Ground
P1425 - 002 - Lower Limit Exceeded - Intermittent
17525 - Oxygen (Lambda) Sensor Heating Circuit: B1 S2: Short to Ground
P1117 - 002 - Lower Limit Exceeded - Intermittent
17843 - Secondary Air Pump Relay (J299): Short to Ground
P1435 - 002 - Lower Limit Exceeded - Intermittent
17829 - Secondary Air Injection Solenoid Valve (N112): Short to Ground
P1421 - 002 - Lower Limit Exceeded - Intermittent
17697 - Boost Pressure Control Valve (N249): Short to Ground
P1289 - 002 - Lower Limit Exceeded - Intermittent
17949 - Fuel Pump Relay (J17): Open Circuit
P1541 - 004 - No Signal/Communication - Intermittent

any help is highly appreciated, thank you

lenat

reason for this problem was stuck piston rings on all 4 valves at once. Root cause unknown.

x19

Well,
The 1st,right now you have lower compression 30 psi, and you removed valve cover off and you can put thickness gauge to check the valve clearance ( should be "0" if compression OKay),but you have a clearance (valve stem bent and stuck at point) which means, you need to remove cylinder head for recondition of the head or If you were lucky,there is no bent in all valve. Therefore, you have to find another place such a valve timing and cylinder leakage test (10~20% OKay too). if those test are passed, Turn crank shaft few times by hand and feel good= no interference, retest compression(=be careful).

2nd,
You have to go next problems (engine management system Pxxxx) after you could start Engine( collect above problem first! ). x19