View Full Version : My 540i/6 has sleep apnea!


Drum
05-13-2008, 10:18 AM
The 1997 540i/6 that I inherited from my Dad has had "sleep apnea" for a few years now. When it was my Dad's, he drove it pretty regularly until Spring time when he would start rolling on two wheels whenever he could. During the good weather, the 540 would sit, sometimes for weeks before it would be driven again and, eventually, my Dad would discover that the battery was dead as a door nail.

We ultimately "fixed" the problem by buying a second battery and carrying it around in the trunk. When the car went dead, my Dad would simply switch the battery and take the dead one for a charge. Somehow, the car seemed more resistant to dying with the battery in the trunk. (How do it know?:cool)

We have a brilliant and very loyal indy BMW mechanic who has been over the car at length and has not been able to figure out where the electrical draw originates.

When this problem first appeared, the battery would die after a week or ten days of no driving. More recently, since I inherited the car, it has been conking out the battery if it goes for 3-4 days without a ride.

Now, I think of the car like one would a dog that needs to be walked on a regular basis. I take it for a long-ish 30 minute drive about once a week and everything stays happy and electrifying. Still, if that fourth day comes and I have not given her a good ride, she is dead.

I figured it might be a good idea to spell all this out for you clever guys here and see if any of you have had similar experiences that you were able to track down. While driving a 540i on a regular basis is not what I would generally consider a burden, I have just recently picked up a used X3 to help save some of the miles on my beloved 5. With the novelty of the "new" car and so on, I am afraid that I am going to have problems again with my 540.

Any thoughts or helpful comments would be appreciated.

1. One symptom that has caught my attention in this is a winding sound that continues, sometimes long after the car has been turned off. My mechanic tells me that this is the vents under the car opening and closing. He has checked this aspect and does not think that it is the cause of the drain, but my Mom tells me that she would occasionally hear the car winding in the garage, hours after my Dad had parked it.

2. Has anyone any experience with the solar panel battery charger offered as an accessory by BMWUSA? It would appear that it sits on your dashboard and converts sunshine to a trickle charger that plugs into the car lighter. As the car has been living outside at my house, it is often quite sun bathed.

Cheers and thanks in advance for any help you all might be able to render.

Drum

jda2000
05-13-2008, 10:48 AM
Common failure in this car, replace the final stage resistor(FSR).

graphicjunkie
05-13-2008, 10:51 AM
I don't have the BMW one, but I picked up a cheapo from harbor freight.
1.5W solar charger for $10.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=44768

I was using it for a few weeks until I got my alternator changed out. Since I don't drive much, it would recharge my battery while it sat. Worked awesome! Plugs into your lighter, and goes to town.

Drum
05-13-2008, 10:57 AM
Common failure in this car, replace the final stage resistor(FSR).

Thanks. When I read this, I called my mechanic and he told me that this was one of the first things he tried. He went on to say that my car has the most recent version of the FSR already installed.

So... could it be a bad FSR that I got? Is there a way to test the function of the FSR?

Thanks again and also for the tip about the Harbor Freight charger. I have one of those stores nearby.

Cheers,
D

cegeste
05-13-2008, 11:37 AM
When I purchased my car, I had the dealer pull up the service history. My FSR had been replaced twice, as well as the battery. I'd say give it another go.

TyroneShoe
05-13-2008, 11:46 AM
I don't have the BMW one, but I picked up a cheapo from harbor freight.
1.5W solar charger for $10.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=44768

I was using it for a few weeks until I got my alternator changed out. Since I don't drive much, it would recharge my battery while it sat. Worked awesome! Plugs into your lighter, and goes to town.

I wonder how hard it would be to take one of these things and hardwire it into the car and put the solar cell on the rear shelf or something like that. Might make a really great trick for wintering your car and/or being a little green.

FrankMstein
05-13-2008, 12:35 PM
Mine was a bad aux fan and it took a meter and yanking all the fuses to find it then the fan. I am not sure if it is a resistor or fan itself...anyone know that?

Drum
05-13-2008, 03:06 PM
Thanks again, guys.

I am off to Harbor Freight for the band aid and I will ask my mechanic to order me another FSR for experimentation.

Thanks for the ideas.

D

Qsilver7
05-13-2008, 04:21 PM
DUDE!!! Please save your money...from what you describe there is NOTHING wrong with your FSU.

It is normal for a battery to fail if the car is not driven for long periods of time and the battery is NOT kept charged. Its a natural affect called SULFATION. The lead and lead oxide (the active material in the battery) react with the sulfuric acid in the battery's electrolyte (fluid) to form lead sulfate. Lead Sulfate (when kept charged) will continue to split and seperate back into lead and lead oxide as long as the battery is being charged...thus producing energy. If the battery sits for long periods without being charged...the lead sulfate begins to crystallize and cling to the plates in the batttery instead of remaining active in the battery's electrolyte (fluid).

The longer the battery is allowed to stay in a discharged state...the lead sulfate resists being converted back to lead & lead oxide...it will eventually kill the battery as the lead sulfate will remain in a crystalline form...clinging to the plates NOT producing energy. That's why BMW recommends disconnecting the battery if the car isn't driven for 3-4 weeks.

BMW also recmmends recharging the battery on a regular schedule if the car is not driven for long periods of time (the trickle charger will work great that you are looking to purchase)

This is also covered in the OWNERS MANUAL. If you don't have an owners manual...you can download one from www.e38.org/e39 ....just look at the bottom of the left column and download the manual (in PDF format) that is closest to your model year.

http://www.bimmerboard.com/members/q/original/Battery%20Storage.jpg

During the winter...I mount my 5 series with dedicated winter tires and the 7 doesn't get driven much. I keep the battery charged by hooking it up to a battery charger every 3 weeks (20 hours @ 2 amps)...which is more than what BMW recommends....but it works for me and I don't have problems with the battery in the 7 going dead.

http://www.bimmerboard.com/members/q/original/BMW%20Battery%20Charging%20Calendar.jpg

Drum
05-13-2008, 05:01 PM
Thanks very much for all that info. I really appreciate that and I understand what you are telling me about the FSR/FSU.

If my car would only die after 3 weeks, this would not be a problem at all, or not very much. The trouble is, my battery is dead after less than a week.

Maybe my batteries have been degraded by all the draining, but the batteries themselves do not remain for very long in a discharged state. Generally speaking, I discover their discharged state and have them re-charging within a day of discharge.

However, I have now installed the 1.5 watt version of the Harbor Freight solar panel charger and I also bought the 5 watt version if 1.5 turns out to be too small or not powerful enough. I guess I will let it sit now for a week or so and see how the battery responds. Supposedly, the solar panel only needs daylight and not necessarily sunshine to generate power.

We shall see.

Thanks again for the suggestions.

Cheers,
D