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Mk5 Unusual Electrics Problem

electrics battery wont start

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#1 FiestaFiasco

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Posted 11 June 2012 - 09:01 AM

2004, Fiesta Zetec, 1.4L, petrol, manual

Car recently developed some odd symptoms which I think are a problem with the electrics. Any advice gratefully received.

Just in case it is relevant - Car lives on a fairly steep drive, nose pointed up hill, and has been parked unused in fairly heavy rain for 2-5 days between uses recently.

Wednesday 6th (last week)
First use in a couple of days.
3 very short drives (5 mins each) with car parked and engine off for 5 mins in between each drive.
Started fine and ran fine but I had the ABS and handbrake lights turning on and off as I drove.
I assumed the brakes might have rusted and got stuck (as has happened before) so I did a bit of sharp braking and releasing to unstick them. No obvious change. The lights may have sometimes been triggered by me braking but not obviously.

Monday 11th (today)
First use in 5 days.
3 very short drives (5 mins each) with car parked and engine off for 5 mins in between each drive.
Started fine, battery really seemed to have no trouble turning the engine over, sounded normal etc. Also ran fine.
This time I had just the battery light on. Was a little worried that at one of my stops the car wouldn't start again, but no problems.
After the 2nd stop I started also getting the ABS and handbrake lights coming on and off (battery light is constantly on).
Then the radio started playing up, going silent, randomly losing the signal and searching etc.
Then I noticed that the windscreen wipers were slowing down, starting to judder, I put them up to full speed and they still crawled. Engine was still running fine.
Parked on the drive, nose up hill as normal. Turned off the engine.
5 Minutes later I had to go out again but I couldn't start the car.
Battery seemed completely flat, groaned and couldn't even turn the engine over once before giving up. LCD displays of fuel and temperature did some funny patterns then calmed down. I tried the engine once more, got the same feeble effort from the battery.
I took my wife's car out instead, for 10 about minutes. Returned and parked ready to jump start the Fiesta.
Gave the fiesta one last chance before rolling it out of the drive and the car started perfectly first time, no suggestion that the battery had any trouble.
I decided to turn the car around in the drive, to make it easier to roll out should I have to jump start it later.
Noticed that the battery light was still on, handbrake and ABS lights were not but windscreen wipers and radio were still acting odd.
Parked the car nose downhill this time. Turned off the engine and out of curiosity tried to turn it back on again.
Acted as if the battery were totally flat again.

So I seem to have a battery that goes flat while the engine is running, then charges itself when the engine is off. I am pretty sure physics says this is impossible so I assume the problem is somewhere in the electrics not the battery. I had a look under the bonnet, but I didn't really know what I should be looking for. I couldn't see any obvious frayed cables or connectors sitting in puddles of water.

Any suggestion of what it could be, or any diagnostics I can do?

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#2 Dan62

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Posted 11 June 2012 - 10:14 AM

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#3 FiestaFiasco

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Posted 11 June 2012 - 02:14 PM

Could you give me a clue what the altenator looks like or how to find it?

Drum shaped thing with lots of looped copper wire, next to the big exposed moving belt, bottom left as I stand in front of the car looking into the bonnet?

#4 Dan62

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Posted 11 June 2012 - 04:52 PM

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#5 FiestaFiasco

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Posted 13 June 2012 - 10:22 AM

Nothing obviously wrong with connections on altenator or battery.

Took some battery voltages on Monday:
Off voltage: around 8.0 if the car has only just been turned off, rising to 10.2 when the car has been off for 30 mins
Idle voltage: starts around 7.2, dropping to around 6.7 over 5 minutes
Idle voltage with max load (lights, wipers, fan): wipers got slower, lights got dimmer, couldn't get back round to the battery to test voltage before it stalled.

Started the car this morning, battery light was on initially then turned off. I put on all the loads but nothing I could do would make the problem return. Lights are bright, wipers are fast and the battery light stays off.

Only things that have changed is that I parked the car the other way on the hill (nose down) and it has stopped raining. Is it possible that water had collected somewhere causing a short circuit?

Weird.


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