Flat battery, v. high current drain - Fuse No. 8 under bonnet. Water pump continuous...

Bit of an update. Big thanks to ph001 - ammeter arrived this morning courtesy of Amazon.

V. pushed for time today but couldn't resist a quick test. Firstly testing at the battery (with boot light on) current draw was 18.8Amps (more than twice my estimate which suggests battery was in better condition than anticipated when fitted, worse when checked and perhaps the drain reduces over time).

I've then checked a few accessible cables under bonnet. I haven't been able to tie this down too much but i'm getting nearly 15A at the fuse box under the bonnet. (See pics). Also I can hear a high frequency buzz near the front of the engine. I don't think it was the alternator but near by. Sounded a bit like a whirring pump (oil pump?) but it was a bit noisy outside so hard to tell. I'll find a metal rod to use as a stethoscope and see if I can narrow it down. Meanwhile any suggestions?
IMG_1444[1].JPGIMG_1429[1].JPG
 
Newbers said:
V. pushed for time today but couldn't resist a quick test. Firstly testing at the battery (with boot light on) current draw was 18.8Amps (more than twice my estimate which suggests battery was in better condition than anticipated when fitted, worse when checked and perhaps the drain reduces over time).
Click to expand...

Is this with ignition off? That is colossal I would expect this to be less than 100mA (you need to give a short delay after ignition off as some ecus may initially draw higher current then go to sleep).

If it is with ignition off I would recommend pulling all the battery fed fuses one by one each time returning and see if you can find a single fuse that causes it to drop considerably. By looking at the fuse diagram you ill be able to narrow down the issue.

I did a post with all the fuses and if they were ignition/aux/battery fed if it helps.

http://www.z4-forum.com/forum/viewtopic.php?f=2&t=99155&p=1451269&hilit=fuse#p1451269
 
I remember seeing that post and thinking it as very community spirited of you but that I didn't need it! Does that refer to the internal fusebox?

I only recorded substantial load from one of the red cables off the battery. I suspect this one heads to the small junction box on the bulkhead then to the fuses under the bonnet. I guess the other feeds the internal fuses. I could be wrong but I suspect my problem is under the bonnet and could be a faulty relay which is not turning off something in or around the engine.
 
You won't get an accurate reading by clamping it around multiple cables like that, as some will be positive and some earth. You need to use the clamp around individual cables to get a proper figure.

Mike
 
Ducklakeview said:
You won't get an accurate reading by clamping it around multiple cables like that, as some will be positive and some earth. You need to use the clamp around individual cables to get a proper figure.

Mike
Click to expand...

Agreed. All the same there are a lot of electrons hustling their way down that conduit!
 
Newbers said:
Ducklakeview said:
You won't get an accurate reading by clamping it around multiple cables like that, as some will be positive and some earth. You need to use the clamp around individual cables to get a proper figure.

Mike
Click to expand...

Agreed. All the same there are a lot of electrons hustling their way down that conduit!
Click to expand...

You can't trust ANY part of that reading, there could well me 15ma going through there...

Mike
 
Not quite how it works. Clamp ammeters work on magnetic field, so if you have say 10A flowing down one conductor and then 10A flowing in the return then the mag fields cancel out and the net result is zero. This is why you don't get a reading clamping around 3-core mains cable for example.

In a car, it's unusual to run a separate 0v cable as chassis is 0v anyway so they tend to just terminate locally to chassis. I suspect that current is genuine so now it's just a case of trying to isolate.

OP, have you had a good feel around the fuse box for anything getting warm as previously suggested?
 
I had the same issue, turned out to be the nav drive constantly searching for the disc after key was removed. I ran a separate live back to the fuse board connected to a circuit which is only live once ignition is on and its been fine since.
 
ph001 said:
OP, have you had a good feel around the fuse box for anything getting warm as previously suggested?
Click to expand...

Not yet - I was a bit pushed for time. Initial indications are that it will be a fuse in the box under the bonnet rather than in the cabin. I'm basing this on the fact that one of the red cables off the battery showed only very low (expected current). The other which I think is the fancy one that runs under the car, to the JB on the bulkhead (I think). I'm registering a good few amps on conduits coming in to and out of the smaller fuse box under the bonnet so (again I think) the fuse protecting whatever is at fault is in that smaller black fuse box.

I'm struggling about to find a wiring diagram that covers the electrical stuff on the engine. I've got the WDS disc here but the only laptop with a DVD slot has an old version of Java and I can't get it on my wifi to update :-x !
 
It finally stopped raining long enough to go and get a bit deeper in to this. In this fuse box under the bonnet: IMG_1448[1].JPG
fuse No. 8 IMG_1447[1].JPG is the one that is carrying the load (an indicated 14A acknowledging Mike's comments about multiple cables in the bundle). The fuse was warm.
No key in ignition but definitely got a whirring noise somewhere at the front of the engine. I wasn't in a position to be able to get underneath but just wondering about the water pump. I'm aware of water pump problems (not sure if these are with N52 engines) but my understanding is these normally fail off. Just wondering if there could be a problem with the thermostat which is causing the pump to default to on.

Can anyone tell me what that fuse no. 8 is actually for?

Also - anyone got a wiring diagram that covers engine functions or a map of the fuses in this box?
 
I'm assuming if you pull that fuse the whirring stops? You would even feel the water pump buzzing if it was running so that is your first port of call. Really struggling to fund any info on under bonnet fuses. Here are the glove box ones just for future ref.. http://www.z4-forum.com/forum/viewtopic.php?f=3&t=38888

The water pump would fit the bill at that sort of current draw, but yes....unusual for them to fail always on. It certainly can run with the ignition off though if the coolant temp is >90'c so you could see how a fault could give you the problem you are seeing. The stat itself has no sensors on it so is completely autonomous. I'd probably still be tempted to change though if you end up doing the pump.
 
Pulling fuses to check for a parasitic draw is not a good idea with modern cars. It is not an accepted practice anymore.

Modules shut down as their power supply is interrupted, then take ages to go back to sleep. Sometimes as long as 20 minutes. Get a normal multimeter and shut as many things as you can (doors, boot, bonnet etc) and put the multimeter leads across each fuse in turn. Right at the top of the fuse. Those 2 metal bits. DC voltage scale. Small range. 2V or less.
If the circuit is active there will be a very small voltage drop across the fuse. If it is not active, it will be 0. The slightest reading (no matter how small, and it will be small) is a sign of current draw.

Andy
 
andyfanshawe said:
Pulling fuses to check for a parasitic draw is not a good idea with modern cars. It is not an accepted practice anymore.

Modules shut down as their power supply is interrupted, then take ages to go back to sleep. Sometimes as long as 20 minutes. Get a normal multimeter and shut as many things as you can (doors, boot, bonnet etc) and put the multimeter leads across each fuse in turn. Right at the top of the fuse. Those 2 metal bits. DC voltage scale. Small range. 2V or less.
If the circuit is active there will be a very small voltage drop across the fuse. If it is not active, it will be 0. The slightest reading (no matter how small, and it will be small) is a sign of current draw.

Andy
Click to expand...

Hi, I’m surprised that a voltage drop can be measured across the fuse? After all it’s a single piece of wire in effect (if it’s not blown!) I would have expected to read 0v measuring across it this way :?
Rob
 
If there is current through the fuse it will have a volt drop across it but it will be small (milli volts). I don't see any issue in pulling it to see the effect though to be honest, despite it not being best practice.

The OP already knows fuse 8 has current through it as it is warm.
 
Smartbear said:
andyfanshawe said:
Pulling fuses to check for a parasitic draw is not a good idea with modern cars. It is not an accepted practice anymore.

Modules shut down as their power supply is interrupted, then take ages to go back to sleep. Sometimes as long as 20 minutes. Get a normal multimeter and shut as many things as you can (doors, boot, bonnet etc) and put the multimeter leads across each fuse in turn. Right at the top of the fuse. Those 2 metal bits. DC voltage scale. Small range. 2V or less.
If the circuit is active there will be a very small voltage drop across the fuse. If it is not active, it will be 0. The slightest reading (no matter how small, and it will be small) is a sign of current draw.

Andy
Click to expand...

Hi, I’m surprised that a voltage drop can be measured across the fuse? After all it’s a single piece of wire in effect (if it’s not blown!) I would have expected to read 0v measuring across it this way :?
Rob
Click to expand...

If the resistance is zero, there will be zero volt drop. But a fuse has a resistance (so has a cable or wire) so there will be a voltage drop. The resistance will be very small though, so the voltage drop will be also.
The key here is if the multimeter reads anything at all, there is current flow in that circuit.

Interesting isn't it?
 
ph001 said:
If there is current through the fuse it will have a volt drop across it but it will be small (milli volts). I don't see any issue in pulling it to see the effect though to be honest, despite it not being best practice.

The OP already knows fuse 8 has current through it as it is warm.
Click to expand...

Thank you for your honesty!
It is not best practice because it is interrupting power to modules. You then have to wait possibly 20 mins + for it to go back to sleep once the fuse is back in. Any current monitoring during that time will be inaccurate because the module(s) are still consuming current.
Checking across fuses in circuits does not affect the power to that circuit.

A business (mine included) hasnt got time to wait 20 mins + each time a module power supply is disconnected and reconnected. Not even considering the effect on the software with power being switched on and off quickly. How fast can you say corruption and reprogramming and well,.....cost.

Yes, I am aware he has found the circuit at fault.

Heat cameras ( infra red) are now being used as diagnostic aids to see where the heat is in a circuit or circuits. Expensive (£500 +) though they may be. TIPM ( totally integrated power modules) or intelligent fuse boxes ( chrysler especially) are good examples where heat build due to current drain deep.inside the component can be seen but not felt.
Sorry to interrupt the thread, but may help someone out in future.

Andy.
 
You must log in or register to reply here.

Similar threads

V
Flat battery - Unable to start car
Replies
4
Views
996
B21
B21
P
Flat battery
Replies
14
Views
1K
DonDon
D
C
Battery going flat
2
Replies
25
Views
2K
Clw
C
G
Very flat battery.
Replies
5
Views
1K
B21
B21
H
Flat battery - cause?
Replies
7
Views
500
enuff_zed
enuff_zed
Back
Top Bottom