As I was running errands this morning, I noticed a progressively louder squealing noise from under the hood. When I stopped to check it out, I could hear it wasn't from the belts, water pump, or alternator and it sounded loud from underneath the car - more like it was coming from the back driver's side of the compartment. As I made my last couple of stops, I could feel the engine surging a little while stopped at a light, and when I would start the engine up I would get a little puff of white (not oil) smoke from the exhaust. When I was a quarter mile from getting home, the engine started to miss and the service engine soon light came on. When I got home I checked the fault codes with my Peake reader and got: 8b 4b 46 3e and 39. These ought to relate to: electric thermostat final stage (I get this one all the time), misfire random, misfire cyl 8, misfire random, and misfire cyl 8.

I fear a cam bearing, but what do you folks think? I plan on having it towed to a local independent BMW shop on Monday, but what should I prepare the wife for, $1000 or $12,000?

1998 540iA

It sounds like the same problem I had two weeks ago. When you step on the gas does the sound fade away?
With mine the more i drove the squeeling became progressively louder, and smoke came out of the exhaust.
The problem w/ mine was the crankcase ventilator went bad. I've never heard of it before, until then. But basiclly it's a PVC part, costs <$100 from the dealer, but it's located underneath the intake manifold, so w/ labor the total was around $500. I spoke w/ the service manager and he said the smoke(which was white) is from oil being sucked through the engine. The car can be driven for a few miles w/o any damage, but the more you drive it, the more oil will be burnt, so basiclly if you drive it long enough you will suck the oil from the engine, and then you're at $10,000. I can't remember why they said it caused the squeling noise.
If the problem just started and the dealer is within 20 minutes from you then drop it off. If not, I'd get it towed, b/c you don't want to take a chance.

Yeah, that's exactly how my situation played out. The only thing I question is why I would get multiple misfire fault codes from only one cylinder (though it could be that cylinder has slightly less compression than all the others - or something). So far I've done all the maintenance on this car, but I'm in the process of moving, so I don't have the luxury of spending two days underneath the hood messing with the intake manifold. I guess it'll go to the dealer Monday. I had hopes that the catalytic converter had failed and would be covered under the EPA warranty, oh well.

Thanks for the heads up, Bud.

You were right on, Man. Laurel BMW in Westmont, IL changed out the intake plate and the thermostat today. I wish I got the labor rate you got, the bill for just the intake plate job was $1000. If I had more time (in the process of moving) I would have done the job myself. Both items had only about $200 of parts. Thanks for the help.

THIS SOUNDS EXACTLY WORD FOR WORD MY SYMPTOMS...can someone please tell me what the part is and where it is located. You said crank case ventilator, is that the actual name of the part. I have this problem right now and no regular mechanic has been able to figure it out.

On my 1997 540i, the part is 11-61-7-501-563 just listed as "Cover" in BMW parts but some people call it the "Oil Separator Valve." It is a plastic cover that contains a large rubber diaphram that fails. It is the part on the back of the intake manifold, held in place by 7 torx type screws. Although not real easy, it can be replaced without removing the intake manifold. I found a real good writeup with photos on E38.org for instructions on replacing the oil separator valve. The part was $75.05 at BMW of Murray in SLC, UT.
The sound from under the car or back of the engine is, amazingly, the sound of air being sucked into the crankcase through the main rear seal. This is due to a huge vacuum developing in the crankcase when the rubber diaphram fails. I was fortunate that Kurt, the shop foreman at the above mentioned dealer, would take a phone call from me and explain, because I would not have believed that the extremely loud screeching sound (like metal-on-metal, or a squealing bearing) that I could hear most loudly near the flywheel under the car was air going through the seal. I was sure the torque convertor, flywheel, or rear main bearing must have failed.
The white puffs of smoke from the exhaust and fouled plugs causing misfire are also symptoms of this failure, since it results in excess oil in the intake manifold. In my case, after putting the car on ramps such that it was raised in the front, the oil ran back and into the left rear cylinder, causing huge "puffs" when I revved the car, fouling this plug, and causing a Check Engine fault.
A quick diagnosis is to pull the oil dipstick out, which allows another path for air to enter the crankcase, and therefore stops the screeching sound from the rear seal.
And just one other bit of knowledge regarding the intake manifold, at least on my '97 540i. There are two throttle sensors located at the front of the intake manifold. One senses the position of the main throttle, the other senses what is called the "secondary throttle" which is activated by a cable and motor and is part of the ASC system. (This is that idiotic system that prevents you from being able to accelerate when the wheels are slipping in snow...I wonder if the genius who designed this ever actually has driven in snow???) Anyway, unlike anywhere else I've ever seen on a BMW (or most other modern cars), THE PLUGS ON THESE TWO SENSORS ARE REVERSIBLE! They are right near each other and it's real easy to reverse them. If you have become accustomed (like me) to not paying too much attention to the possibility of reversing electrical plugs on your BMW since they are ***ALWAYS*** idiot-proof, then you should know that there is at least one instance where it is NOT idiot-proof! When I made this mistake, these were the symptoms: ASC light on dashboard remains permanently lighted; car will not upshift in forward gears but remains stuck in first or second; ABS light is NOT on; an ECM code is not set, so you won't find one with a regular OBD-II reader, but if you have access to Carsoft or other more sophisticated code reader, there is a code set on the ABS/ASC system. The Carsoft code was "38 Gas-Valve-Adjustment Error."

Chalk up another for the good ol' crank case vent valve.