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Hi there, having a big issue with my mini cooper S rs53 its a 2002 with around 90 thousand on the clock.

Iv encounter a issue where cylinder 1 has less than 50psi and rest are 175? Which causes the car to missfire.

I have changed spark plugs an ignition coils an leads what else could be the issue?

In need of big help.

Thank you.
 

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changing plugs and coil pack or leads wont fix low compression ,, you next job would be to redo compression test on number 1 this time add a 50ml of engine oil in the plug hole first, the retest it if compression jumps to same as other or as near as then its a piston ring issue, if stays same then valve issue or gasket problem as the cylinder next to it has good pressure i would guess more likely a cracked valve,, if its a burnt out valve then i would suspect the injector has gone wonky and over fuelling or dripping rather that atomising needs checking before rebuilding the head etc as will just do it again if faulty ,,, could also do a leak down test if have a compressor and some air line and taps and special adaptor to screen in plug holes, but doing a oil compression test does work well
 
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