Trying to find a prob with the Batterys going flat after only being 6 Mths old.

The Batterys are at 12v when the ignition is on but wont start the car. Needs a jump.

When running the batterys show 13.5v so the alternator seems to be charging.

All the wires are attached correctly.

Any advise will be very much appreiciated

Thanks

Nige

The car needs a

Disconnect the earth and put an ohm meter across the positive and earth to see if there is anything drawing power, could be something like the mini transformer in the radio

13.5 is on the low side when running. I would expect 14 - 14.5 ish. Check and clean all battery connections, engine earth strap, condition of wires ( they're long in a B I think) alternator connections. Fan belt OK? Then retest. If still under 14 then check alternator.

Common cause for this problem with Lucas ACR type alternators is a diode going short on one of the phases.As suggested,check for current drain with everything switched off. You dont even need an ammeter to do this.Just disconnect one battery terminal and gently strike it on the battery pole,a spark indicates current drain.

quote:

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Originally posted by Dusty
If still under 14 then check alternator.

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Hi Cryoman,

I've been having some electrical problems with my MGB recently so I feel your pain.

What actually happens when you try turning the engine over?

Without knowing more, the first things I would suggest doing are:

1) disconnect all the battery terminals, and the main earth connection in the battery compartment. Give everything a good clean and a little sand to make sure it's good metal everywhere.

Try ignition again.

2)check the engine earth strap (left hand side of the engine straddling the engine mount)

Try running a jumper cable between the engine and some clean point on the chassis as a test. If the car starts with that in place you know it's the earth strap.

3) check all the starter motor connections. Famous for getting corroded as they're quite low to the ground.


Hope that's of some help, I've found that it tends to be really simple things that go wrong, and they tend to only require very simple solutions.

[Edited on 10/8/08 by ravingfool]

MGB starter pre-enage solenoids are a pain in the neck for sticking -- try giving the starter a hefty hump.

If that dosen't work ---

13.4 volts is about right for one of these cars with the engine at 2500 rpm & head lights switched on, it dosen't mean the alternator isn't the problem.
With everything thing switched off I would expect the battery voltage across the two batteries to fall to 12.8 to 12.5 volts --- 12 indicates a problem probably the batteries are discharged.

First problem to check for is the the 3 spade plug at the back of the alternator is making a clean tight connection that isn't arcing as this is a very common problem with ACR aternators. To fix this you have to remove the black plastic cover and clean the blades with a nail board pinched from the swimbo then give the lucar connectors in side the plastic case a squeeze in, enough so as the bight into the blades.

if that dosen't work get back to us, it could be the alternator diodes allowing current drain back through the alternaor or a dead cell in one of the batteries.

[Edited on 10/8/08 by britishtrident]