3 replies to this topic

[gazdude]

Hi guys, my 1999 Mini Cooper MPi has been great since I bought it last year but now its a bit poorly

About 3 months the battery was losing its charge a lot so I bought a new Pug 306 diesel battery which did the trick! But once again I'm having problems with the battery draining (sometimes below 12v!) and hence the car won't start. I've been solving this by putting it on charge every night but as its my daily runner I could do with repairing it asap!

I've done a search on here and tried all the following

1) Got battery checked out at two places who said its fine
2) measured the voltage at the alternator (14v+) and the battery (13.5v+) when the engines running
3) cleaned up engine earth and battery earth, checked the under the car lead, cleaned up alternator connector
4) made sure alternator belt is tight enough
5) checked battery in series and drain was only 0.03amps, think it was due to alarm/immobiliser being on?

Halfords seemed to think the alternator was on the way out, they got me to start the engine and turn the lights on. This caused the battery volts to drop from 13.5v and when the heated windscreen was on it dropped to 12.9v! The alternator stays at a constant 14v+ though.

Should I just stump up and get a new alternator or can I check a few other things first?

The car seems to be kangarooing a bit now as well

Thanks for any help, might have to go to Himley 2moro to see if theres any bargains

[tomsbluemini]

Sounds like an engine earth strap to me...

will probably only cost you a fiver to buy, and to be honest, ifyou can check the voltage on your battery you can change an earth strap, not that hard...

You'll find it as you look at your engine, there's a steady bar on the left hand side of the block. there's a braided metal wire coming off it - it's that one...

Tom

Edited by tomsbluemini, 10 May 2008 - 02:07 PM.

[sixwheeler]

An earth strap cannot cause a current drain on a battery!

The normal cause (having ruled out ALL other obvious possibilities) is a dodgy diode in the rectifier pack on the back of the alternator allowing a small current drain.

If you only do very short journeys then over time the battery can become flat.

You need to check the amount of current draining (oh, you already did that, I personally think that is a bit high, but not over the top and I doubt that is enough to discharge it over night (duff battery?), you could certainly expect a 0.015A drain which is what my minis are at the most and this does not cause any problems) while the car is off and then my first check would be to unplug the the alternator to see if the drain stops. If that is not the cause then you just have to keep going unpluging things and pulling fuses until you can work out exactly where the problem is.

Also, make sure all the connections are good and rust free on the solenoid and that the battery straps are well fitting and very secure as well as the alternator and solenoid connectors on the ends of all the wires. Any voltage/current that you loose in poor connections is not going to get to the battery to charge it up.

Edited by sixwheeler, 10 May 2008 - 04:16 PM.

[gazdude]

Hi guys!

Finally seem to have it fixed, I was checking the ECU earth instead of the engine earth d'oh!! The engine earth was connected to some terribly corroded points, tried to get it out but its in the most inconvenient place ever, couldnt get a good grip of it.

Decided to fit a new earth from a point on the engine block to the chassis. This seemed to make the alternator volts near enough match the battery volts while the engine is running.

Took it out for a spin and now the kangarooing seems to have dissapeared, just gotta see if the battery charges up fully on a longer run.

Thanks for the advice guys.

(also need a new battery negative clamp as its a bit loose! )

Edited by gazdude, 10 May 2008 - 07:54 PM.