# "Battery drain" 1988 BMW 735i



## donaldashworth (Dec 10, 2007)

["battery drain" 1988 BMW 735i]

I recently purchased a 1988 BMW 735i with 197k miles from the orginal owner last weekend. Some time

back, the engine's main bearing was replaced, and pretty much the entire engine was overhaulled. The

body also has a new pearlescent white paint job.

The orginal owner decided to sell car after all of this work because quite regularly the battery would

completely drain itself "while running". The car runs great, the battery just dies everyonce in a

while.

Last night, I connected two wires to the battery and routed them outside of the vehicle and let the car

set for an hour. Later I connected my fluke and I am measuring a 0.01 milliamp draw...nothing

practically. So, unless I have an intermittant parasitic leak, I believe the problem may be caused by

the regulator or altenator.

I started the car and let it warm up, and then disconnected the battery. The car remained running on

the altenator. This does not mean the altenator is not defective, but it's not completely dead either.

My question is this; how would one proceed at this point? I do not want to take the car to a

dealership. I can spend 38.00 and replace the regulator, and 180.00 or so on a rebuild altenator later.

I have 2003 BM 325i and I am strapped for cash. The 735i (having a new paint job and rebuilt

motor...and all of the maintenance records) was too good of a deal to pass up. I would rather make

educated guesses on parts replacement rather than non-educated ones.

Can anyone think of any other diagnostic treatment, asside from taking the altenator for a diagnostic

check up at Autozone?

Thanks,
Don


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## TerryY (Jul 20, 2003)

Just drive it to autozone. I believe that they should be able to test both the battery and alternator in the car.


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## manminder singh (Oct 15, 2007)

Hi I had the same problem last year and It was the final stage blower resister. After a year of trouble free motoring I am now having the same problem with the battery draining when the car is parked. I am now told by the main BMW dealer that it is the BASIC MODULE which is at fault.
I am now posting a thread on beamerfest with my problem.


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## donaldashworth (Dec 10, 2007)

manminder singh said:


> Hi I had the same problem last year and It was the final stage blower resister. After a year of trouble free motoring I am now having the same problem with the battery draining when the car is parked. I am now told by the main BMW dealer that it is the BASIC MODULE which is at fault.
> I am now posting a thread on beamerfest with my problem.


Thanks Terry,

I have a Bently Manual for my car. Before I tear into the wiring diagrams, can you tell me off hand how to test for a defective final stage blower resister?

I know the characteristics of resisters. Just wondering if there are any "tricks" before I take it out of the circuit and test it.

Thanks,
Don


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## TerryY (Jul 20, 2003)

Testing my long term memory here. If the final output resistor has failed the blower will only run at the last/highest detent on the speed wheel. Because that bypasses the resistor and applies full voltage. Been a long time though and my memory is slipping in old age.

http://www.e38.org/e32/

or

http://bmwe32.masscom.net/

may have the correct/definitive answer.


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## donaldashworth (Dec 10, 2007)

*Parisitic battery drain update - I'm at a loss*

This afternoon I disconnected the negative battery terminal and place my digital volt meter between the battery negative terminal and the body ground. I set my DVM on mA/A (DC) and the display would vary between .38 and .45 mA.

I let the car rest for 30 minutes and began pulling fuses one at a time under the hood. I eventually reached fuse 20 (the plastic fuse cover labels fuse 20 as "Instrument cluster, heater")

My Bently Manual describes fuse 20 as&#8230;

Anti-theft system (DWA)
Automatic climate control (IHKA)
Brake pad warning
Instrument cluster check control 
On board computer
Park, tail, marker, under hood lights
Power windows
Sunroof

I am not certain if this is .38 ~ .45 mA is the normal draw across fuse 20 when the car is idle.

Also, occasionally the fuel and temp gauges on the instrument cluster do no resister. When this happens, the digital readout does not work either. Usually, after I drive the car around a bit, the instrument cluster returns. Not always though.

And the SRS light always flashes. I am not certain what is causing this. I checked out the left and right collision sensors&#8230;they seem ok.

One thing I noticed today is the speaker/chime has been disconnected. I reconnected the speaker/chime and, event with the windows and doors closed and the car was turned off and at rest, the speak chime would go off (one ding) every few minutes. I am not certain if this was due to my bumping/touching the car while taking fuse readings or not. I have to assume that the previous owner disconnected this because it kept going off. I went out side a few minutes ago, and I could hear the speaker/chime sounding.

The previous owner said that the electrical problem (parasitic battery drain) began when he drove through a water puddle at high speed. He could not diagnose the problem, and his solution was to put a negative terminal "quick disconnect" on the battery.

At this point, if the .38 ~ .45 mA current draw across fuse 20 is normal, I would think that I should begin understanding why the speaker/chime is sounding. I am leaning towards disabling (if possible) the "Anti-theft system".


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