Strange Engine Issue That Nobody Seems To Be Able To Diagnose - Please Help.

[CraigRobbo]

Okay guys, super weird one here, my old engine (m52B28) started running rough (and i mean rough) revving slow and sounded like it was running on 3 cylinders. Here is a short video, So we changed the the Crank, cam lamba sensors and the maf but it got worse and then eventually it dropped a valve and died, now to me it sounds like its pre detting.

So i thought nothing of it and assumed the engine was ready for dying any ways. So changed the block to a known good working block, exactly the same issue! Sounds like its running on 3 or massively pre detting, so again changed sensors and tried unplugging knock sensors..no avil...so we tried a new ECU which was known working from another car...same issue...WHAT the hell guys... so in total 3 engine blocks known working good same fault in this car, two ECU and replaced all the sensors twice.. what could it be??
In the video that is full open throttle and that is how slowly (and maximum) it revs...however now it wont even rev past 2k now.
Video uploaded so you can hear how it sounds but remember it got worse than this.

Please help.

[jrmurray]

This may sound stupid but what haven't you changed in the car? Like ignition system etc cuz if you've replace main components then surely it must be something that is still original?

[CraigRobbo]

I think ive gotten to the bottom of it, the cats...