BMW e38 electrical issues

E38-beemer

Hi folks,
Need advice here.
Scenario: My 1998 e38 is having some electrical issues currently. Something has been draining the battery over the last 2 months when the car is off. A quick boost of my wifes' car and it would be grand again for a few weeks until it would go again.. Last week, it was a dead duck, no amount of charging would start the car.

So what do I do. I was thinking do I get the AA to bring it to the nearest auto-electrician (I'm based in swords) and take a chance with him or do I bring it to a BMW dealer straight away? Just really concerned about the cost of finding and fixing the root cause. I'm hoping it is something simple but then again it may not be..

Any advice or voices of experience would be greatly appreciated..
Just want some good advice on where to go with this one...
Thanks a mill...

Stevie Dakota

Are you sure it's not just a battery that needs replacing? I has a similar problem with my BMW and a new battery solved it. How old is the battery in the car, if more than 5 years it needs replacing. I would certainly try that first before anything else.

Anan1

Stevie Dakota wrote: »

Are you sure it's not just a battery that needs replacing? I has a similar problem with my BMW and a new battery solved it. How old is the battery in the car, if more than 5 years it needs replacing. I would certainly try that first before anything else.

+1, it is that time of year after all. If the new battery goes dead then at least you can jump start it and drive in to Hamiltons.

E38-beemer

Hi Stevie,
I would be surprised if it is just the battery as it is only a year old... and it was a good one that i bought at the time..
When the AA came out to me the last time to boost it up (as i'd no one around to use booster cables) they did a drain test on the battery and confirmed that when everything seemed to be off in the car, he could tell using some piece of equipment that there was still a drain on the battery - he even climbed in the boot of the car while testing it just so to make sure it wasn't the boot light staying on..
Hence why I think it is an electrical issue... so any advice on where to go?

Anan1

Hamiltons are good and not too expensive, they're based just off Camden St.

Seth Brundle

Get out a multimeter and remove all the fuses one by one and see if the drain on the battery stops - this will help narrow down the cause.
Out of curiosity, how long is the car standing before the battery drains?

Fishtits

"Get out a multimeter and remove all the fuses one by one and see if the drain on the battery stops - this will help narrow down the cause.
Out of curiosity, how long is the car standing before the battery drains"

+1 ... btw you dont need a multimeter - remove a battery terminal (negative) and touch it against the battery pole, if it sparks you've got whats known as a parasitic draw... this is bad.

Remove & replace each fuse in turn, until you identify which one, when removed reduces/eliminates the spark on touching the battery lead to its pole.

At this stage its a process of eliminating the various loads fed by that particular fuse.

Slow methodical process

unkel

E38-beemer wrote: »

A quick boost of my wifes' car and it would be grand again for a few weeks until it would go again..

You can fully charge the battery, but if you leave the car for a few weeks without starting / driving it, it most likely will not start. No point in getting the multimeter out or start messing with fuses, I'm telling ya

If you want to keep the battery fit, but do not want to drive the car, start it up once a week and leave the engine running for 30 minutes...

Voodoomelon

E38s are renowned for eating batteries for breakfast, but you should be able to start the car after a week of no driving no problem. You should also get your alternator checked. What's the mileage like, and what model is it?

rebel.ranter

Is it related to the "Hedgehog Resistor pack"? There is a unit called a final stage unit that controls the heating. If it has failed it can cause the fan to run on for 16 minutes after the car has been switched off. A long shot but could be your problem.
I have seen it go on two cars, both were e39 5 series but I believe the e38 7 has the unit also.

http://www.bimmerfest.com/forums/showthread.php?t=143393

However, with the amount of stuff on standby in these cars it would not be surprising if the car didn't start after a couple of weeks, especially when it is not in regular use. If I were in your shoes I would set up some sort of trickle charge system for the car. You could ring something up with proper connectors in the boot so it would be less hassle than connecting up a trickle charger with crocodile clips, etc.

unkel

Yep as others said, big difference between one week and two weeks. My E38 doesn't have a hope of starting after two weeks, but will always start after one week

unkel

rebel.ranter wrote: »

I would set up some sort of trickle charge system for the car. You could ring something up with proper connectors in the boot so it would be less hassle than connecting up a trickle charger with crocodile clips, etc.

A €15 2W solar panel trickle charger could do the trick, provided the panel can be placed in a reasonably bright position. You can hard wire it to the battery

nogoodnamesleft

As suggested multimeter and measure the voltage across the battery to see if it is anywhere near 12 volts. Start the car and turn on some electrics, lights, rear window heater etc and measure across the battery again. This is to check if the alternator is actually charging the battery should be in the region of 14volts across the battery terminals. If it isnt you know the alternator isnt charging it.

rebel.ranter

You could also check to see if there is an excess current drain with a multimeter.

Checking for current draw:

1. Disconnect the positive terminal from the battery.
2. Connect the Multimeter in series between the positive terminal of the battery & the disconnected cable.
3. The current draw of the car should be about 0.7 amps when everything is shut down. It should stay at that level for 16 minutes, then kick into a "sleep mode", with a draw of 0.02 amps. It should stay at this level indefinitely. If you have an after market alarm or a badly fitted car kit or different stereo, etc. the level will be slightly higher.
4. If you notice that it is significantly higher than the values mentioned above then you may have something faulty or an unwanted current draw. To eliminate the various circuits have an accomplice pull each fuse individually (do one at a time) until you notice a drop in current draw on the multimeter.
Don't get too excited when you see it drop off altogether or even significantly, you may have only disconnected something that is meant to draw that amount current!
Make a note of the fuses that affect the reading noting what items they power. Through a process of elimination then you can determine whether the readings are right for those that draw current. There's lots of BMW specific or even e38 specific fora (forums) out there to help with this.

Battery Reading:

Just to note that the battery should read higher than 12V, it is more like 13.8V

Also if you are only using the car as an occasional use car perhaps consider installing a higher Ah battery. The Ah is Ampere Hours, i.e. It will allow the battery to run things for a longer period of time. I think the e38 has a 70Ah battery as standard, get a 90Ah or 110Ah battery.

There are even people that have installed 2nd batteries! (see resource below), however this is probably over kill. In work we have installed 2nd batteries to cope with some of the test gear installed. You can use 2nd battery for emergency starts too by pressing a button on the dash .

BMW 7 Series Resource:

http://www.e38.org/

Voodoomelon

Can't beat the second battery, the 750 comes with one as standard. I was considering doing a retrofit of a second battery to power my extra equipment, as you can buy the dual stack battery rack no problem.