Apologies for yet another cylinder 3 misfire thread, but we have done some troubleshooting already and are at a roadblock and we need help please. 2013 Mini Cooper S, 55k miles.

To summarize, a friend's car stalled in the middle of an intersection, was tower to dealership, they quoted a crazy amount to have fuel injectors, spark plugs, brakes and oil changed.

So we decided to do it ourselves. Everything replaced that the dealer was going to do themselves, and the car runs smoother than before, but still misfiring on 3.

Swapped coil pack from 3 to 2, cleared code, code came back still cylinder 3 misfire. Kept car running, went down the line and unplugged coils from all cylinders to try to notice a difference in how the car ran, 1,2, and 4 did as expected, car ran worse when unplugged.
Again, we took a known good coil (one that when unplugged made car run worse), put it in cylinder 3, then plugged 3 while car was running, and it made no difference.

We are now thinking it may be the wiring harness going to the ECU from the coils because the actual connector on 3 does not look corroded at all. We peeled back some of the mesh around the wiring on the harness where it visually looked the most scuffed up, expected a short of some sort, but the wires looked fine.

 

How about a compression check? Maybe your exhaust valve disintegrated.

 

Will do a compression test and get back with results.

Thank you.

 

Yeah, just saying as there are quite a few cases - me included - with chunks from the exhaust valve missing. I believe there is no root cause analysis why it's often No.3.
But hopefully I'm wrong. Could also be some carbon buildup on the intake side. That now goes down to removing the intake and so on.

 

We did just change the oil and there was no sparkling in the oil or metal chunks on the drain plug magnet indicating that, so hopefully not.

We did just change out fuel injectors too, but didn't think to check the intake valves while the manifold was off.

Thanks again,

 

There will be nothing in the oil. It just melts away and exits via the turbo.

 

Compression test came back to about 190 psi consistent between all cylinders.

I took the spark plug out with the coil and i couldn't see a spark when turning over the engine, but i could've been doing it totally wrong. Coil packs were replaced before performing this test.

Any help would be appreciated!