Oh dear...

[wasted]

You were right :) I should always remember that the basics are the most important bit!

[wasted]

Seems I spoke too soon. She pulled her little 'trick' again last night, leaving me stranded in Kingswood - however once again, after waiting for an hour and a half and then jump starting her, she happily drove home with lights on, charging with no worries at all. Again, no warning on the discharge - no ignition light - and it discharged VERY quickly, going from a fully charged battery to nothing within ten miles of driving with just the stereo on.

I'm now thinking this is something that's triggered by the engine getting hot and causing something (the alternator?) to stop working.

Next step is a new alternator I think - anyone able to shed any more light?

[Funky Diver]

If your battery is discharging that quick, I would say it's something more sinister than the alternator and you cxould be throwing muney away on the alternator.

It sounds more like the battery is somehow getting a direct earth to the chassis somewhere, more than likely via a faulty connection earthing out causing the discharge. When / If it happens again, check the heat of the battery. If it is very warm, than that would be your problem.

[PeteGLi]

- do you lot still reckon I should replace that earth strap on the coil mount?

I would.

[PeteGLi]

Next step is a new alternator I think - anyone able to shed any more light?

Before splashing out on a new alternator, it is worth getting a local auto-electrician to test it on his bench equipment.

[wasted]

Good shout on the battery, but I forgot to mention that the car actually died as though it were starved of fuel, indicating that the alternator isn't feeding enough power to the engine to run the fuel pump or provide a spark. If it were the battery earthing, I'd expect it to run normally until stopped - then on starting, the battery would be flat.

I think it's likely to be either the alternator failing when hot or wiring from the alt to the engine being dodgy... I've been wrong before though. Does this make sense?

[wasted]

Pete - how much do you reckon a test would be? It's just that I have a replacement alt available for about £15, meaning it might be more economical to just replace it. On the other hand, if it's not faulty, it is a waste of cash!

[PeteGLi]

My local one did mine for free.

[wasted]

Worth a go then! I'll have a ring around :)

[Nate]

take the battery off and clean the terminal posts and the wire clamps. do the same for the main earth lead where it joins the chassis and the g'box. with engine running (jump started or recharge battery) check for voltage drop from alt case to battery -ve and from alt +ve to battery +ve

[wasted]

Cheers Nate - I'll give that a go.

[ianaudia4]

If you have access to a battery charger, fully recharge the battery that way. I still think your battery is goosed!

[wasted]

As above, Ian, I reckon if it were the battery the car would continue running until switched off, because the alt would carry on supplying power to the engine even after the battery was totally flat. I had a think about things last night and I reckon the alternator's the most likely culprit given the symptoms, so I'm going to bite the bullet and replace it anyway.

[ianaudia4]

If your battery was goosed your electric fuel pump would not work! I have 2 spare alternators mate, if you want one?

[wasted]

I have an alternator available actually, so thanks for the offer but hopefully I'll be ok!

I think I'd be inclined to think it were the battery if it were just one or two things failing, but given that the lights, the instrument lighting, the MFA and everything else electrical gradually dim/die/stop working just before the engine coughs to a halt, I think it's more likely that the alternator is not providing power to the engine. Whether that's due to wiring or the alt itself is yet to be determined.

My Dad and I were discussing things last night, and we reckon that there is a set of diodes in the alt that could break down as they get hot... Would that make sense?

The other possibility given the fact that the ignition light doesn't come on was that the blue exciter wire was fubared, but since the ignition light goes on when the engine dies, there's obviously electricity moving through that circuit, so that rules it out. Brushes are also unlikely, given that the ignition light doesn't come on as the battery is discharging, so there must be something else going on inside the alternator that's causing this.

Could still be wiring though... It's hard to diagnose, as it seems to only happen when the car's hot, and even then, not every time. I had considered letting the car idle until hot and then popping a multimeter on various points to see where it fails (if it fails), but I have no idea whether this would work.

The alternator pulley's been whining for a while now, so I think I'm going to replace it anyway, run it for a while, and see if the fault reoccurs - one essential purchase in the near future will be a jumpstarting block I think!