Xsara Picasso missfire

[Vuk1987]

Guys, I have a bad missfire that has gotten worse and worse.
Error codes on Lexia are
P1336 permanent
P1337 permanent
P0313 permanent (might be due to using lpg as main fuel)
P1339 permanent

I also did a live measurements, but video is too large to attach it.

My question is, should I just go for the ignition coil change, or there are other things I should look for before that?
Spark plugs are some year or two old, with no big mileage.
I have change ignition coil pack some 3 years ago.

The car is Xsara Picasso 2006 year of production, 1.6 16v petrol engine TU5JP4 or NFU is, I believe, the engine mark.

Thanks in advance.

[Vuk1987]

I've searched on the internet a bit. I will measure the compression first.

[Vuk1987]

Measured the compression, it was 10 bar on cylinder 1 and 4, it was 7 bar on cylinder 2 and 3. I used cheap Chinese measuring device so I guess there is a possibility it's wrong. But, the engine should be able to run with that compression, although it's far from perfect.
I changed the ignition coil, but I don't notice any difference.
I'm going to erase errors now and watch the situation from now on.
No luck for now

[Vuk1987]

Well, there actually is a difference. Check engine light went off on it's self, and the car seems to run better. But the sound is still awful.

[Vuk1987]

The mechanic measured the compression with his professional tool, and it turns out it is lower than it was when I measured it with my cheap barometer (5,5 bar on two cylinders and 8,5 on the other two), so, the engine is pretty much done. I use LPG, and it has probably done its job the valves, at least I hope so. I hope it's only valves, not piston rings. We'll know in a day or two. It's gonna cost me, anyway ...

[PaulC5]

It could be the cylinder head gasket has failed between cylinders 2 and 3 so might not be too expensive to fix.

[Vuk1987]

It was around 750 euros to fix, although I replaced front disks as well. Cylinder head gasket failed, two engine valves burnt.
Now I get error code P0337, permanent fault, engine speed sensor signal coherence.
I guess that they moved something, or made dirty, but I can't tell yet.
I'm yet to find the sensor, and see whats wrong. The engine runs better, but behaves strange on higher rpm