My R53 has been throwing P0302-Misfire Cyl #2 codes off and on for about 8 months. I've had it to three shops, including the dealer, with no permanent solution, each shop works on it for a bit, code goes away and they say its fixed, the next week, it recurs. I've changed out the entire ignition (coil pac, plugs, wires), swapped injectors around, cleaned injectors and the terminals on injectors and grounds, replaced the fuel filter. It's always cyl #2, and it starts to misfire at idle after some time at speed, then it will clear out until I come to a stop again, it doesn't accelerate from a stop as smoothly as it used to- it kind of stammers and at speed (when running without the misfire) I have to modulate the throttle to get acceleration rather than mashing it (which makes it bobble). The ECU has been sent out and checked good, I'm at a loss. Any thoughts or previous experiences would help. BTW its at 162k miles with the original SC, 15% SC pulley, 2% OD crank pulley, JCW CAI, Miltek exhaust if that helps at all.
TIA,

 

Suggestion: turn off the DSC at startup. My R53 was "stammering" from a stop and this cured it (no idea why but I suspect the ECU was restricting fuel flow for some reason). I will say that mine was not throwing a code, however, so this may not work for you -- worth a try though.

 

Have you checked the connector that goes to the ignition coil? (the engine compartment wiring harness side) Might be some corrosion on the pins there causing problems. I know others have had that issue before.

 

 

Cooper48- I forgot to say that I'd tried that, to no avail.
Mike87- I thought that the corrosion issues were on the plug wire side, not the harness side- that'll be my next attempt
Tgriffithjr-no idea, I'm not sure where to hook into the fuel rail to measure it-I do know that it should be 3.5 bar (50 psi) though

 

The ignition harness can also chaffe about 6-8 inches down the harness from the ignition plug. Take apart the loom and you may find some of the insulation worn off the wires.

 

Thanks, I'll check out both that and the corrosion issue at the same time.

 

Have you checked compression or leakdown on the cylinders? My R50 is doing the same thing on cylinder 4, I did all the same items as you. Finally checked compression and cylinder 4 has zero compression. Suspect a burnt valve as Mini's apparently like to do that, so I'm currently hunting for a replacement head or rebuild.

 

+1 on a compression/leakdown test if it has not already been done. I too was having misfires in cylinder 2/3. Turned out Compression in cylinder 3 was only 2/3rds of the rest. Long story short, warped/Cracked head.

 

I found the immediate cause. I decided to change the plugs even though they only had 20k miles on them- here's what I found with #2 plug:


I haven't cleaned it up and put it under the microscope yet, but I'm betting that its got a crack in the insulator....The arcing burned all the way down the insulator and across the plug wire boot to the (I suspect) plug tube. Just a little bit of oil on the seal, so I'll probably get a valve cover gasket kit and do them all up properly just to be sure.
Microcracks at the top of the insulator just below the contact. We'll see if the new one cracks after use as well... NGK BKR7-EIX plugs FWIW