[Lotus77]

I'm new to BMWs and thought some people may know an answer to this. I hear marble like sounds from the intake side of my E91 325, close to the cylinder 1 end. Any ideas?

I also have a check engine light and my mechanic says the code is from a misfire. I have 100,000 km/60k miles and so decided to change the spark plugs. Just did them tonight. Plugs 1-3 had quite a heavy deposit of carbon. Plugs 4-6 were a bit white, but seemed pretty normal. Any ideas here?

[pmeloche]

I has an misfire problem on one of the cylinder of my X5. The ignition coil was at fault. What octane grade are you using? Are you following the recommendation of BMW found in the reference manual?

[Lotus77]

I got an OBD reader and I think the primary problem is the O2 sensor. 'O2 sensor stuck lean bank 1 sensor 1'. I would infer that's why plugs from cyl 1-3 are heavily carbon fouled because the ECU is putting more fuel into those cylinders since the O2 sensor is stuck at lean.

[pmeloche]

O2 sensors are also prone to failure and will trigger the CEL.