Cracking sound from engine

[treff-7]

I checked fuel pressure. It was only 3 bar so swapped the FPR. Now pinging is almost completely gone and engine runs smoother and pulls harder.
I only drove the car for about a mile since and it seems like that little pinging is slowly going away, too. We'll see tomorrow how it behaves. I might reset the computer as well.

Bottom line: Thank you for everyone who tried to help!

Techno55:
I tinkered with the cams when I swapped the vanos but triple checked the timings after. I did not change the fuel filter as it was replaced a few years ago. However I might replace it again just for the heck of it.
When I installed my Walbro pump I searched the net for pictures how to do it and saw that people had very dirty pickup filters on their fuel pump. Mine was like new with 270K on the clock. I bought this car 7 years ago and I did not replace it. And knowing what condition it was in then I highly doubt that the PO had it replaced either. I don't know if it's because this car never ran on low quality fuel or the ethanol wiped it clean...

[the imitator]

I bought a fuel pressure gauge and while i drove the car without the cap on it sucked up a lot of oil due to that major vacuum leak

If that happens again to you, just use your gas cap.

[treff-7]

I'm quite embarrassed to say but it did happen again. This time however the cap slid off the engine and got stuck in the engine bay so i was able to put it back. Stupid, i know.....

Thanks for the tip BTW! I had no idea it fit.

[treff-7]

Engine is still pinging... not as bad as it was before and it's a lot more responsive and starts easier. Also noticed when i hooked up the gauge that after shutting the engine off the fuel pressure was gone in about 30 seconds. I don't think it's still the case cuz it starts very easy even after sitting for an hour.
Fuel filter is next on the list. I think techno550 will be right and the ethanol is playing a joke on me.... I hope at least. I'm running out of options.

[treff-7]

I checked the fuel pressure again. It was under 3 bar this time so replaced the fuel filter. Engine got significantly better but I can still hear slight pinging once in a while for under a second and then DME adjusts the timings and it goes away. I will check on fuel pressure again tomorrow if it's still low but looks like the knock sensors are working fine at least.