for someone who can pull the heads. You could have anything from bad or broken rings, bad valve seal and guide to a hole in a piston. If you can't pull these yourself, you'll need to take it to a mechanic to do so.
Bought corsa 1.2 sxi as first car which worked fine for 2/3 weeks since i bought it (there did feel like a very slight misfire when i accelerated hard). I noticed two days ago it had absolutely no oil left so refilled with 5w30 synthetic and it worked great... for one day... broke down on the M8 the following day with substantial power loss amd engine warning light. I managed to get going again and got to a garage. Changed all 4 spark plugs (3rd cylinder spark plug was damp and oily) and coil packs AND refilled with oil again. Ran smooth for about 5 mins and began to misfire and lose power again, it now transpires that theres no compression in 3rd cylinder. It seems to me like the oil is having an adverse effect on the performance of the engine ie, leaking onto spark plugs.
Any advice on what this could be or what I should with this would be massively appreciated!