My son has a 2001 BMW 325i automatic with more than 100k miles. Engine has been running rough. He replaced all of the plugs, plug wires and coil packs. His BMW mechanic has told him he has a bad valve on the number one cylinder. My questions are: Is this a common problem for this car? What is the best method for repair, rebuild his head or purchase a rebuilt head?
Not a common problem. I'd like to know more about the car's service and repair history (especially any overheats and codes), as well as the mechanic's diagnosis, before thinking about pulling the head.
FWIW, a very common problem (particularly in winter) around this age/mileage that can lead to rough running is the CCV. If that hasn't been replaced, I'd be asking for a smoke test and a crankcase pressure/vacuum test before I did anything else.
In reply to 02Pilot: No overheat issues in the past. The mechanic ran a compression check and then put a camera in the spark plug hole and spotted the issue. He only works on BMW's in Allentown Pa.
As long as it wasn't overheated, the head can be rebuilt. As far as why, that's tough. Definitely not a common problem on the M54, as far as I know. The only thing I can think of is that it may have suffered the well-known secondary air injection failure and maybe the bits of the pump/valve got sucked into #1?
I would also check the DISA valve to make sure it hasn't disintegrated. Simple to pull it, and failure will be obvious (flap gone or shattered).
The head can be rebuilt, certainly... but one easy thing that commonly causes rough running at relatively low miles is leaks, blockage or failure in the secondary air pump, hoses, valve assembly or passages. A hunk of carbon stuck in a hose can cause issues and a crack in the hose can be a source of unmetered air.
If you trust the mechanic's diagnosis... cool. If you are leery and are seeing codes like P0491 and P0492 and it's usually because the secondary O2 sensor isn't seeing enough airflow when you first start the car (pump only runs for 30 sec or so on startup...).
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