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It's not for my 7thgen but it's for my friends golf gti vr6 it's general mechanics question so I thought I would ask so here goes.

His car is screwed up so we hook it up to vagcom (scanning tool) gives us 3 codes misfiring cyl 4 and 6 and knock sensor. So we take it to the mechanic to check it out he opens up the head cyl 4 filled with gas and cyl 6 is somewhat scortched. So we get it back, change the coilpack, wires and spark plugs that did nothing. So we did compression test should be between 144 to 191 with max variant of 47. Cyl 1,2,3,5 are all around 160-165. 4 is at 85 and 6 is at 130. We put some oil in the cyl 4 to see if we can get the lube around the rings and maybe eliminate that it's a rin problem, the compression goes up at bit to 110. Do the same for cyl 6 but it stays the same at 130. So what were trying to figure out is the following, what would be the problem be? Injectors were thinking that the injectors are still getting pulses so it's not throwing a code and it's a mechincal failure in the injector or maybe its cracked. Maybe a headgasket doubtful but could be a crack in between the gasket 4 and 6. The other thing were thinking is the valves or the piston rings. The engine has 73,000km which is like 45,000miles so were not really leaning to the rings but you never know. We're gonna take the intake manifold off tommorow and check the injectors so hopefully that will narrow down some solutions. Anyways do anyone have any idea of what it could specificly be?

 
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You've mentioned pretty much all the possible causes. Most of the cases I have seen where a cylinder has low compression has been because of the piston rings or valves.