Sudden massive misfire?

Hey! I wanted to go for a drive in my 172 ph1 today and was greeted with a strong smell of unburnt fuel along with what seems to be a massive misfire right upon starting - car was shaking and sounded like it was going to cut out any moment. Could it be running on three cylinders? It was completely fine three days ago.

Spark plugs, coil and leads were done half a year ago along with injectors. If I remember correctly, there was a little bit of oil on the leftmost (UK drivers side) plug. Also changed the thermostat, cooolant temp sensor and coolant tank last week, if that could have anything to do with it. How do I solve this?

Start with the basics. Make sure that everything is connected as it should be. Don’t rule out that one of the new parts has failed. I don’t know anything about the ph1 but if it’s like the ph2 make sure that the leads have not been trapped underneath the inlet manifold.

Unburned fuel and lumpy idle sounds like you're down a cylinder. You can try individually unplugging HT leads (with the engine off) to see if one has no impact on how it runs to find the cylinder thats not firing.

Thank can easily swap plugs, leads and injectors around to see if you can isolate a specific component before proceeding.

Thatd be my approach. Check all plugs as well, I found I was running rich once and it had soaked the plugs. Giving them all a clean solved the issue short term. Obviously did nothing to fix the root cause.