Weird current drain

[bmw540]

Hello all again...

I am slowly getting to the source of my electrical issues. First was a low battery issue which has been resolved by getting a new battery:( . Then I had a current drain issue:( . This was caused by the rear window blind, so removing the fuse has fixed the issue. Now I have another current drain. :( I now have my multimeter fixed to the dash watching the charge voltage and have noticed the voltage drop down from 13.9 to 13.0 when the engine gets hot. Is there a fan or something which turns on when the engine gets hot? as the voltage goes back to 13.9 when cold, like a ECU fan or something. I am going back to the drawing board tomorrow when I get some time to pull fuses. Hopefully the drain is there with the ignition on.

Any ideas please let me know.

[billy]

Hello all again...

I am slowly getting to the source of my electrical issues. First was a low battery issue which has been resolved by getting a new battery:( . Then I had a current drain issue:( . This was caused by the rear window blind, so removing the fuse has fixed the issue. Now I have another current drain. :( I now have my multimeter fixed to the dash watching the charge voltage and have noticed the voltage drop down from 13.9 to 13.0 when the engine gets hot. Is there a fan or something which turns on when the engine gets hot? as the voltage goes back to 13.9 when cold, like a ECU fan or something. I am going back to the drawing board tomorrow when I get some time to pull fuses. Hopefully the drain is there with the ignition on.

Any ideas please let me know.

firstly if you have the multimeter on the dash, where are you taking the charge feed from? unless its on some hefty wires direct from the battery you arent going to get a good read - you may already know that - just asking

also a current drain while the car is running shouldnt really be a problem as the alternator should be able to cope

[BillionPa]

there is an ECU fan, but i think i read somewhere its not thermostat controlled and runs all the time

[BillionPa]

also, a current draw that would drop the system voltage by that much would be.... massive, like a stereo amp, or some kind of electrical heater.

[bmw540]

yeah something is going on but did not get time last night to have a look as the wife is due any day and needs me to help out... so car comes second at the moment.

The meter reading on the dash is voltage not current as have been advised I will blow something up and the current will be too large to measure.

The voltage drop only happens when the car reaches operating temperture. Runs perfect when cold.

I have removed the radio fuse and no change.

On my way home tonight will pull the aux fan and see if there is any difference.

Is there a fuse for the ECU fan that I can check.

[shogun]

I only know it from my E32: the small fan for the E-box has the size of a PC fan, have my doubts that this could be the culprit.
I runs at 2 speeds. Always on, and when the temp in the e-box exceeds 44 degree C or so it switches to higher speed.
If it goes bad, it will start 'singing' like a bird.

[gmannino]

E34's all have tons of electronics to go wrong. Most of the time current draws are small electrical circuits that drain your battery everynight until the battery will not hold a charge anymore. Car audio, video, etc, most of the time, do not present current draws, but sometimes it does happen. I've fixed hundreds of current draw problems.

-Take a test light (the ones with the bulb)
-Disconnect the negative side of the battery and connect the probe between a good ground and the negative side of the battery.
-With the car not running and the ignition key out, the test light should be bright or glowing.
-Pull each fuse, ONE AT A TIME.
-When that light goes out, you have found the exact circuit the current draw exist.
-Investigate circuits individually, one at a time, to find draw.

IF you still dont find one, start pulling your fuseable links.

hope this helps

[bmw540]

only problem is that it only happens when the car gets hot so it going to be a pig to find.

[gmannino]

So how do you know you have a current draw? Does the battery die everynight? When the car's running, all electrical will draw from the alternator. The car gets hot everytime you drive it.

[PaulJ]

After the engine is hot (13 volts), what happens to the voltage when you turn the headlights on?

Paul

[Bill R.]

the ecu or ebox fan is thermostatically controlled, it comes on at 44c and goes off a 36c




there is an ECU fan, but i think i read somewhere its not thermostat controlled and runs all the time

[billy]

i still dont know why you are concerned with a current draw when the car is running...

your only concern should be is that the alternator is putting out the correct voltage to be able to run the car and charge the battery

can you let us know what problem you are having?

[bmw540]

thanks for all the replies...

Gmannino. I can tell there is a current draw by watching the charging voltage and the idle gets rough. The battery does not go flat over night. I have done a current test with engine off and it is drawing less than 100mA. Sorry for the term "hot", I mean correct operating temperature. The engine warms up correctly and does not overheat.

PauJ. With the engine hot the voltage when cold drops around 0.4vdc and driving ar0.1vdc.

Billy. I want the car to run correctly. I don't want to have it just charging the battery with an electrical problem that is going to bite me in the arse sometime knowing my luck at night. The crust of the problem is that the charging voltage is very low then the engine is at operating temp and at idle. All other times it is fine.

I notice last night when I was at the traffic lights and the voltage was 11.8vdc and accelerated the voltage went to 12.5vdc and then all of the sudden jumps back up to 13.8vdc.

cold start voltage is around 14vdc
hot start voltage is around 12-13vdc

cold and at the traffic lights voltage is 14vdc
hot and at the traffic lights voltage is 12-13vdc

cold and driving voltage is 14vdc
hot and driving voltage is 14vdc

So I am wondering if the aux fan is kicking in with a large current draw when the engine is at operating temperature at the lights.

[BillionPa]

sounds like the alternator is messed up, diodes perhaps?
you would need to be running the low beams, the high beams, the aux fan, the fog lights, and blasting a huge stereo to drop a 140A alternator anywhere close to 11.8V

remember, my test of all the lights + stereo + interior fans on full blast was still above 14V.

[bmw540]

i really hope not as i had the alternator removed and tested and they said it was fine. Was pissed that they did nt chnage the regulator. But then again I get the correct charging voltage when the car is cold and when driving. Only happens when at idle.

[BillionPa]

when they tested it, they tested it at room temp, and not when it was as hot as the engine..... speaking of which, is the cooling vent on the bottom attatched?

[billy]

when they tested it, they tested it at room temp, and not when it was as hot as the engine..... speaking of which, is the cooling vent on the bottom attatched?

billionpa - i think your just confusing matters
you shouldnt be concerning yourself with what is consuming power and what switches on when the engines hot etc

your concern should be that the alternator isnt kicking out enough power

i would hazard a guess that the brushes are worn down on the alternator and or the regulator is faulty

get the alternator back out and change the regulator assembly

billy

[BillionPa]

that shouldnt confuse matters at all.

when his alternator is at op temp and moving at low rpms, its not kicking enough voltage. therefore, the unit is either overheating, or is failing at normal operating temp.

next step would be to determine which case, and the first logical step would be to see if the cooling vent fell off, as it requires only visual confirmation.

if that fixes the problem, all is good for now, if it doesnt, move to step 2 and pull the alternator.

[bmw540]

Ok update...

Besides the charging voltage problem I have been also chasing a rough idle issue. I had the fuel filters changed yesterday afternoon and it has made a huge difference, also seams to have resolved the charging voltage. Let me explain. After changing the fuel filters the idle is now around 600rpm from 400-500 rpm, idle is a lot smoother and the charging voltage is now around 13.5-13.7vdc at idle with the engine at normal operating temperature. I have also noticed at idle that the charging voltage is not steady, it fluctuates between 13.5 and 13.7vdc. Is this normal? I think you are both on the money about the alternator not being 100%. I will have it removed again and get another guy to test it and change the voltage regulator.

So to sum up…
Flat battery
Purchased new battery and had alternator removed with bearing replaced
Flat battery
Found voltage drain in wiper pressure control motor. Removed fuse
Flat battery
Found voltage drain in rear window blind. Removed fuse
Low charge voltage
Changed fuel filters
Next is remove alternator and test and replace voltage regulator

Thankyou for all of the support and help… I can sleep well tonight.