When I bought my '05 MCS, I found out it had been bought and serviced at Tate by the previous owner. I went to Tate and got the service records for my files.

I've noticed over the last few months that the car seems to peter out in the upper rev ranges, mostly above 4K. I thought maybe the air filter might be the culprit, so I replaced that last week with the K&N drop-in. It didn't make much difference.

So, on a whim, I went and bought a set of new plugs for it today. I started replacing them when I got home this evening, and when I pulled the first one I noticed it had a four-prong configuration. I didn't think much of it, as the plugs said BMW and NGK on the barrel; obviously serviced by the dealer, so they couldn't screw that up...right?

Wrong. I replaced the plugs, took it for a spin, and WOW!! What a difference! She pulls cleanly all the way to the redline now; no gaps, no uneven acceleration, nothing. When I got home, I checked out the NGK part number on the old plugs - BKR6EQUP. That's great for a standard Cooper, but not for the MCS. I checked the service records and sure enough, Tate had replaced the plugs about 10K miles ago.

Nice.

 

Actually the NGK BKR6EQUP plugs are for both the Cooper and Cooper S. The JCW cars normally have their plugs replaced with BKR7EQUP plugs which are a level cooler.

What really might have been the issue is that the old plugs were fouled or otherwise damaged and thus weren't performing well.

 

The plugs I pulled looked OK - a little black around the edges, but the electrodes were a golden brown, with no obvious signs of wear.

All I know is that I put in the correct plug and the car runs better.

 

Did you check the gaps? Maybe Tate just didn't gap 'em? It would be interesting to gap 'em and try them again.

 

Actually if the plugs he pulled were the multiground NGK plugs then they don't need gapping like a traditional plug would. They should be pre-gapped to the MINI spec.

 

Ah ok... all these new-fangled thingamajigs are nice!

 

If they didn't look that bad but it ran poorly perhaps a conductor was cracked? It's possible to crack a plug installing.