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I have a 2007 Cooper S 1.6 Turbo with a misfire, when removing the oil cap there seems to be a vacuum.I have looked around for any air leaks still no joy. Ive tried plugs and all coil packs no luck. Engine management light on and i have had it code read and it comes back with a faulty ECU ?? Ive run a compression test and 1-2-4 are all reading 175. Cylinder 3 is reading Nil.

Can anyone point me in the next obvious direction please. Sticky or burnt out valve maybe ?:crying:
 

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I have a 2007 Cooper S 1.6 Turbo with a misfire, when removing the oil cap there seems to be a vacuum.I have looked around for any air leaks still no joy. Ive tried plugs and all coil packs no luck. Engine management light on and i have had it code read and it comes back with a faulty ECU ?? Ive run a compression test and 1-2-4 are all reading 175. Cylinder 3 is reading Nil.

Can anyone point me in the next obvious direction please. Sticky or burnt out valve maybe ?:crying:
will be a crack valve number 3, ( stick oil in number 3 retest compression if jumps up its piston rings if dont then valve or gasket or cam follower has jumped off on inlet vvt spring maybe,or gasket has gone to oil way maybe, either way head off, as for faulty ecu is that it wont connect to diagnostics or is it because it had a flat battery at some point and that just a bi product of no power to ecu or anything else, reset it full charged battery and re scan it,, also what are using to scan it,
 

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Thanks for that, I guess to start I will re test cylinder No 3 with oil and see where that takes me.
 

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Thanks for that, I guess to start I will re test cylinder No 3 with oil and see where that takes me.
i've seen a fair few valves get cracked or burnt out on them,, mostly a indication of other issues causing it in first place like injector gone wonky or wrong spark plugs or spark plug of coil pack problem very rarely,, worth after repairing do run injection cleaner through it.
that all said some just crack,
you will need head off if were you and repairing it put new chain kit in it as old one will be spent for sure or very close to it. eitherway you need to remove head , but i would before doing so do that trick with oil in the bore and compression test as when head off harder to prove rings good or bad with out further strip down ie sump off and piston out,, the oil will temp seal worn piston rings to give a reading if rings,, if no change then proves more likely its within the upper part of engine,
another test can do when head off is put some diesel small amount in number 3 cylinder with engine oil drained hour before and sump plug out , so pour diesel in and then watch the sump plug hole for any diesel running out,, if instantly get it running then rings have worn out, on a very good engine could leave it in there for days and loose none,, i also use seafoam inlet spray on the pistons and let soak in and down to the rings as this loosens the crud that can hold rings off the bores on some, i also use it to clean head with scotchbrite pads ie inlet ports carbon and all surfaces,, once clean and ready to install head just before put head on i clean both head and block with thinners or panel wipe head this helps the gasket coating to stick its self to the surfaces
 
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