P38A Fixed- Battery going flat again

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Andy Burrell

Andy Burrell

Retired to the country
Posts
190
Location
Cambridgeshire
So I have a couple of jobs to do on the car and have not had it plugged into the Ctek for about a week as it is up on stands at the moment. Needed to turn the ignition on yesterday and the battery was flat again. Since the last time I have removed the rf unit for the remote locking and am just using the key to unlock etc, I have cleaned up all the earth points I can find as well as a new earth from the battery to the engine.
I thought as I have time waiting for other bits to arrive I would test the alternator as this is something I have not looked at properly. To make it easier to test I have taken it off the car and set up a bench rig. I have attached a video of it under test and it looks OK. Will probably get it refurbished though as then I am 100% sure it's OK.
I guess is then a case of disconnecting things to try and work out what else could be causing it. The car has TV screens in the headrests and a PlayStation 2 wired in under the front passenger seat and there is also some mystery wiring under the dash not connected to anything I reckon it had a car phone installed at some point.
The battery is about 9 months old so am hoping it's not that.
Anything else to check?
 
Have you got a DC Clamp meter (this is what I use)? Makes it easy to see what wires have current in them after switch off.

Also if you keep drivers door open, and manually close the door latch, then you can "lock" the car so the BECM sleeps & then check for current drain on wiring inside the car.
 
Datatek said:
Easy enough to refurb the alternator yourself. Flat in a week is pretty quick if the battery is good. Have you done the BECM sleep test?
Click to expand...
I haven't specifically l knew about the rf receiver keeping the BECM awake which I have eliminated. Is there a guide to doing the sleep tests?
 
Datatek said:
Easy enough to refurb the alternator yourself. Flat in a week is pretty quick if the battery is good. Have you done the BECM sleep test?
Click to expand...
I have just sat in the car with it all locked up and the faint glow on the auto P does go out after about 3mins.
With regards to the alternator refurb, I have looked everywhere for the parts to refurb it but have drawn a blank with the Bosch part numbers.
 
Andy Burrell said:
I have just sat in the car with it all locked up and the faint glow on the auto P does go out after about 3mins.
With regards to the alternator refurb, I have looked everywhere for the parts to refurb it but have drawn a blank with the Bosch part numbers.
Click to expand...
Mobiltron do the regulator/brush assembly and maybe they do the diode pack for the diesel, not sure about the V8. Any refurb need a regulator set point of 14.7 volts for modern batteries.
If the LED goes out, the BECM is going to sleep, so the drain is elsewhere. Headlamp wipers not parking correctly can cause problems I believe.
 
pwood999 said:
Have you got a DC Clamp meter (this is what I use)? Makes it easy to see what wires have current in them after switch off.

Also if you keep drivers door open, and manually close the door latch, then you can "lock" the car so the BECM sleeps & then check for current drain on wiring inside the car.
Click to expand...
Been looking at clamp meters, seems to be an array of price and quality. Is there one you would recommend?
 
The one in the link above is what I use, and definitely does DC current. Make sure you read the reviews because there are some with incorrect product details.
 
Andy Burrell said:
Been looking at clamp meters, seems to be an array of price and quality. Is there one you would recommend?
Click to expand...

I would suggest you look for one that has a maximum current rating of 150 amps or less. You are trying to measure a current drain that is probably a few amps and this might be hard to measure accurately on a meter designed to measure up to 400 or 600 amps. The one I use has a maximum of 60 amps and can easily measure the expected 30 to 50 Milliamps of drain expected after the BeCM goes to sleep.
 
So this morning I took the alternator to a man in a shed who has been testing and repairing alternators and starter motors for more than 30 years. He put it on his test rig and immediately diagnosed the problem, the brushes on the regulator module were bouncing and not producing a consistent voltage. Something I wouldn't have noticed with my test rig. He reckons its the original unit and it's done 115k so not too bad. He's going to give it a full refurb for a lot less than a replacement.
I have also bought a clamp meter from a local firm.
https://testermans.co.uk/product/alphatek-tek632-acdc-mini-clamp-meter/
 
Andy Burrell said:
So this morning I took the alternator to a man in a shed who has been testing and repairing alternators and starter motors for more than 30 years. He put it on his test rig and immediately diagnosed the problem, the brushes on the regulator module were bouncing and not producing a consistent voltage. Something I wouldn't have noticed with my test rig. He reckons its the original unit and it's done 115k so not too bad. He's going to give it a full refurb for a lot less than a replacement.
I have also bought a clamp meter from a local firm.
https://testermans.co.uk/product/alphatek-tek632-acdc-mini-clamp-meter/
Click to expand...
Make sure that the refurb includes a regulator with a set point of 14.7 volts which is needed for modern car batteries;.
 
So had the alternator refurbished. The regulator module is no longer in production either by Bosch or as a pattern part so he rebuild the old one with the correct components and fitted new bearings that were rusty and worn, the slip rings were smoothed out and all tested. £95 all in which I was happy with. I now have to methodically work through the wiring to see what's causing the drain as the battery went flat when it was standing without the alternator connected. Not helped with the torrential rain today stopping me getting on. Fortunately its not my main vehicle so it takes as long as it takes.
Also had opportunity to re do one of the driveshaft oil seals I did earlier on as it was weeping, re did the hub alignment and fitted a new LR oil seal and it looks nice and dry now.
Will update as I go. Of course it could still be a knackered battery, only 10 months old.
 
Andy Burrell said:
So had the alternator refurbished. The regulator module is no longer in production either by Bosch or as a pattern part so he rebuild the old one with the correct components and fitted new bearings that were rusty and worn, the slip rings were smoothed out and all tested. £95 all in which I was happy with. I now have to methodically work through the wiring to see what's causing the drain as the battery went flat when it was standing without the alternator connected. Not helped with the torrential rain today stopping me getting on. Fortunately its not my main vehicle so it takes as long as it takes.
Also had opportunity to re do one of the driveshaft oil seals I did earlier on as it was weeping, re did the hub alignment and fitted a new LR oil seal and it looks nice and dry now.
Will update as I go. Of course it could still be a knackered battery, only 10 months old.
Click to expand...
No regulators available as a pattern part? I find that hard to believe. If the regulator is producing only 13.8 volts as used to be the standard, if you do short runs, you will soon end up with a knackered battery as 13.8 is not enough to charge a modern battery fully. If is is 13.8 volts I suggest you put a charger on at every opportunity.
 
It's putting out 14.4v at tick over so that ought to be OK. I charged the battery with the Ctek on the car whilst the alternator was off being repaired and left it standing for 4 days without any driving and the Ctek disconnected. It then was flat enough not to be able to turn over. Will take the battery off and charge it again then leave it sitting on the bench for a few days to see if it holds the charge.
 
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