Car wonโ€™t start - battery fine.

Car wonโ€™t start - battery fine.

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Discussion

paintman

6,573 posts

159 months

Monday 21st June
quotequote all
Ref the post by NMNeil above.

Sometimes I find these multiple quotes using selected bits from longer posts confusing.
That one makes it look as though I'm the one claiming to get 9 years out of my batteries.
Something I've never said!

Edited by paintman on Monday 21st June 19:00

MitchT

Original Poster:

13,873 posts

178 months

Tuesday 22nd June
quotequote all
Still trying to find someone with jump leads. In the meantime, I looked at the connections again.

Thick black cable from the -ve on the battery is connected to a tab on the "dome" containing the suspension strut. There's another black cable connected to the same dome which disappears under the fuse box and continues under the battery. I can't tell where it goes after that.

Nothing else to report!

phumy

5,139 posts

206 months

Tuesday 22nd June
quotequote all
Cheapest I could find and are probably rubbish too but come on, you have to borrow some? Go buy a set

https://www.ebay.co.uk/itm/100-AMP-CAR-JUMP-LEADS-...

E-bmw

6,340 posts

121 months

Tuesday 22nd June
quotequote all
MitchT said:
There's another black cable connected to the same dome which disappears under the fuse box and continues under the battery. I can't tell where it goes after that.
Likely the engine/gearbox/starter in a roundabout way.

MitchT

Original Poster:

13,873 posts

178 months

Tuesday 22nd June
quotequote all
phumy said:
Cheapest I could find and are probably rubbish too but come on, you have to borrow some? Go buy a set

https://www.ebay.co.uk/itm/100-AMP-CAR-JUMP-LEADS-...
Happy to buy some - just won't be able to do it until the weekend.

Penelope Stopit

8,860 posts

78 months

Tuesday 22nd June
quotequote all
Might be a good idea to start from scratch

MitchT

Original Poster:

13,873 posts

178 months

Wednesday 23rd June
quotequote all
Not much to report until I've picked up some jump leads on Saturday, though I'll speak to my local garage guy on Friday anyway.

In the meantime, I discovered that you can test for bad grounds by putting the multimeter into continuity testing mode and attaching the black probe to the -ve on the battery, then touching the red probe on the various earth points. I did this and tested the four ground points that I could find, all of which returned 001, which I believe is as it should be. The engine block, however, which I understand can also be treated as a ground, returned all sorts of random numbers. Maybe the earth cable running from the engine to the chassis is the culprit, but I can only see the end that's attached to the engine block and I can't even reach that.

Anyway, we'll see what Friday brings.

E-bmw

6,340 posts

121 months

Thursday 24th June
quotequote all
You have been told by several people since day 1 that this is a VERY likely culprit and how to test the theory with a jump lead.

Get it tested. wink

MitchT

Original Poster:

13,873 posts

178 months

Thursday 24th June
quotequote all
As I've already said, I'm getting jump leads on Saturday. I can't get them sooner.

Penelope Stopit

8,860 posts

78 months

Thursday 24th June
quotequote all
MitchT said:
Not much to report until I've picked up some jump leads on Saturday, though I'll speak to my local garage guy on Friday anyway.

In the meantime, I discovered that you can test for bad grounds by putting the multimeter into continuity testing mode and attaching the black probe to the -ve on the battery, then touching the red probe on the various earth points. I did this and tested the four ground points that I could find, all of which returned 001, which I believe is as it should be. The engine block, however, which I understand can also be treated as a ground, returned all sorts of random numbers. Maybe the earth cable running from the engine to the chassis is the culprit, but I can only see the end that's attached to the engine block and I can't even reach that.

Anyway, we'll see what Friday brings.
Mmmmm, it don't work like that

Resistance tests are meaningless as there's no load on the circuit being tested, many circuits will pass a resistance test yet fail a volt-drop test under load

Volt-drops are what it's all about

Measure voltage between 2 points when under load

Voltmeter connected between battery negative and engine block, turn key to crank position, 0.25 volts maximum should be shown on the voltmeter, any higher reading points to a bad engine earth

Same volt-drop test can be carried out on the battery positive cable to starter motor

Voltmeter connected between battery positive and starter positive, turn key to crank position, 0.75 volts maximum should be shown on the voltmeter, any higher reading points to a bad positive cable

Note higher volt-drop expected at positive cable, 0.75 volts max

MitchT

Original Poster:

13,873 posts

178 months

Thursday 24th June
quotequote all
Fair enough. I can only experiment with the information I can find until I can get help, which I can't do any sooner than tomorrow anyway.

MitchT

Original Poster:

13,873 posts

178 months

Monday 28th June
quotequote all
Just had the guy from the garage out...

Booster pack on battery: Nothing.
Jump lead from -ve to block: Nothing.
Attempt to bump start: Nothing.

He's now arranging to get it towed so he can get it on his ramp.

Odd how a car can be parked working fine and a month later, be completely dead, even though the battery is fine!

Sheepshanks

24,920 posts

88 months

Monday 28th June
quotequote all
On the upside, at least it has a definite fault. It's a nighmare when these things are intermittant.

MitchT

Original Poster:

13,873 posts

178 months

Monday 28th June
quotequote all
Sheepshanks said:
On the upside, at least it has a definite fault. It's a nighmare when these things are intermittant.
Definitely. I was concerned that it would suddenly and inexplicably work again and then I'd be worried that the fault would return when I'm out somewhere. I'd sooner something is broken and is then fixed, even if it means spending some money.

MitchT

Original Poster:

13,873 posts

178 months

Tuesday 29th June
quotequote all
Garage called and said they couldn't find a fault anywhere, so maybe the key's not talking to the immobiliser - have I got any more keys? I was already using the spare master as the main master had broken - it was one of those fancy (but relatively fragile) ones with a built in torch and it had disintegrated years ago when I used excessive force on a stiff lock. Funnily enough I'd bobbed into a BMW main dealer last weekend for a quote to get that replaced. Anyway, I went down to the garage at lunchtime with the valet key and bingo - engine started! Perhaps if the car hadn't been sat for a month, thus prompting thoughts of battery failure or a seized starter, I might have thought to try a spare key in the first place!

Facepalm.

paintman

6,573 posts

159 months

Tuesday 29th June
quotequote all
Something simple!
And possibly a cheap fix?

Nice to know you've got it sorted.


MitchT

Original Poster:

13,873 posts

178 months

Tuesday 29th June
quotequote all
£80 for "two hours faffing around" as they put it. More than happy with that!

Oh, plus a new spare master key to add to the new master key that I already needed... and hope the valet key doesn't bork in the meantime!

Penelope Stopit

8,860 posts

78 months

Tuesday 29th June
quotequote all
Sheepshanks suggested on the first page that you try another key

Oh well, live and learn

Good that it's up and running

MitchT

Original Poster:

13,873 posts

178 months

Tuesday 29th June
quotequote all
I didn't think I had another key at the time.

The casing on the main master key had broken apart a few years ago when I used too much force on it in a sticking lock. The spare master key - which I'd be using since - was the one that wouldn't start the car. The other key which I have - the valet key - I mistakenly though that one would unlock the car but not start it. Turns out it does start it but won't open the glove compartment or boot.

At least I know what all the keys do now!

Sheepshanks

24,920 posts

88 months

Tuesday 29th June
quotequote all
MitchT said:
The other key which I have - the valet key - I mistakenly though that one would unlock the car but not start it. Turns out it does start it but won't open the glove compartment or boot.

At least I know what all the keys do now!
The valet key is for a parking valet to use - you obviously don't frequent the right sort of places. smile