This time – a short entry, in which I will tell you how the replacement of the valve cover ended quite severely.
The problem: due to wear, the seal of valve cover had become hard, which resulted in the oil leak in the spark plug shafts, and the oil also dripped on the exhaust manifold. Also, the DME Offset type adaptations were unstable. This problem could appear thanks to extra air supply either along with the seal or via CCV membrane. A logical decision – the valve cover has to be replaced!
After replacing the valve cover, the situation with Offset type LTFT got correct. The problems with oil leakage disappeared. But another problem appeared – uneven performance of the engine (shivering), which was caused by quite often misfires. What could be the cause of the problem? The situation with possible misfires should even get better because, during the maintenance, the spark plugs were replaced (original BMW spark plugs, purchased from the dealer, were installed).
On the next day after the service maintenance, the owner of the vehicle took out the ignition coils and found, that the inside of the spark plugs pipes is white, very rough – as if someone has worked it with the sandpaper!
What had happened to the ignition coils?
As the pipes (mostly from outside) were dirty with oil, the mechanic, in goodwill, has “washed” them using a cleaning spray.
Here we have to remember what the Bosch dealer said – these ignition coils can be cleaned only with a dry cloth because the pipes are covered with a thin layer of silicone. If this protective layer is damaged, the ignition coils have to be replaced.
Unfortunately, the spray has permanently damaged this protective layer.
The white “residues” confirm that the high-voltage has chosen the shortest way – it has “skipped” the inside of the pipe of the ignition coil instead of performing the discharge in the spark plug. This is the cause of misfires.
In this current case, two mostly damaged ignition coils had to be replaced permanently, other – should be replaced during the next 5 .. 10’000km. Only after a complete replacement of a full set of the ignition coils, the problem with misfires disappeared. Yes, the customer had extra expenses of EUR 200 for the ignition coils; also, the costs of several diagnostics and the replacement of the ignition coils.