Sorry to shout, but I hope someone out their can enlighten me before Monday.

My E39 528i 5-spd has just over 50K on it. Always serviced by BMW dealerships, by the book. Ran great until yesterday. Suddenly, the CHECK ENGINE light comes on and the car starts riding rough, especially at low speeds.

I took it to the dealership immediately. Three techs spent an hour trying to figure out the problem. They put in new plugs and a new coil with no success. Finally, they did a compression test and found cylinder 3 at only 30 lbs. All the rest were normal! Initially, the service rep mentioned bent valves due to overrev on downshift!? Then he said it could be just about anything. So, they plan to start by tearing the head off on Monday!

Has anyone experienced anything like this with their 528 E39? I really don't want to have the head taken off if it could be software causing this. And, why the heck would only one cylinder be affected and the other 5 are just fine? Even the service rep later discounted the bent valve theory because more than one cylinder should be affected by that scenario. He said the techs can hardly wait for Monday to get that head off and see what's going on - YIKES! I don't want my E39 to be a guinea pig. HELP!

anything - faulty piston rings, blown head gasket, blown head, worn out cam lobes (almost improbable), faulty valve spring retainers etc. You name it. Again, I am saying this based on what you have described. Any of these factors can lead to the loss of compression, at least the way it is tested, and to incomplete burning that caused your engine light to come up.

I know it does not help but you asked the question. Sorry.

Stepan