So first off this is my first post, I just bought an r55 well after running or driving for about 15 to 20 minutes it will start to miss and hesitate consistently on the 4th cylinder I have changed spark plugs , coils, injectors and im getting 165 lbs on compression while warm on very very rare occasions I can blip the throttle and it will backfire through the intake my question is what more could I check , test or change?
also currently I don't have any CEL'S

 

Backfire through the intake leads me to think timing issue

 

there the code I get and if I unplug then plug the eccentric motor my rough idle goes away and i can reset the check engine

 

I also put on a new eccentric valve sensor its an oem unit but no change, is it possible that the motor is going out?

 

Look over this link. A failed knock sensor will pull timing and keep the motor running with retarded timing limiting power till it's fixed.

https://www.pelicanparts.com/techart...eplacement.htm

Could also be the timing chain. This is a all to common failure on the Mini Cooper

 

New knock sensor still not running right

 

Possible problem? Thats the wiring going to the oxygen sensor

 

well crap found my problem

 

What the what?!?

 

🤯That's definitely a problem. I don't think that's gonna buff out.

 

Weirdest damaged piston I've ever seen.

What was the condition of the plug?

You can see where the projections on the piston are pounding indentations in the head. Projections appear to be "chunks" of whatever embedded in the piston. See if they can dislodged.

Why no apparent damage/marks on the valves?

More close ups would be of interest.

Must be a result of FOD, however, condition of the valves is not consistent with FOD. You'd expect to see valve damage as well for FOD. Unless the FO is too soft to mar the valve.

Can't be a coincidence that most of the damage is in the squish bands.

 

15 years of working on cars and this was a first for me
plugs are all undamaged just normal carbon buildup