Alternator or Battery?

[huwants2no]

Hi

Driving 2007 1.9tdi Octavia

Recently it's been sluggish to start cold and warm sometimes. With a jump it's great so I'm guessing that rules out starter.

The battery is less then one year old so I thought alternator.

When I spoke to local garage guy said he would change the battery after I told him symptoms.

I tested battery with multimeter...12V engine off. 14.1 engine running

Also tested alternator to best of my ability with red lead on the cable goes from Alternator to the battery and black lead on alternator housing and got 12.1V

From what I read it should be more like 14.2V there

Anyone think I should buy new battery or does it seem as it is the alternator is bad?

Is there a guide on here for replacing alternator on here??

[Blue8793841]

27 minutes ago, huwants2no said:

Hi

Driving 2007 1.9tdi Octavia

Recently it's been sluggish to start cold and warm sometimes. With a jump it's great so I'm guessing that rules out starter.

The battery is less then one year old so I thought alternator.

When I spoke to local garage guy said he would change the battery after I told him symptoms.

I tested battery with multimeter...12V engine off. 14.1 engine running

Also tested alternator to best of my ability with red lead on the cable goes from Alternator to the battery and black lead on alternator housing and got 12.1V

From what I read it should be more like 14.2V there

Anyone think I should buy new battery or does it seem as it is the alternator is bad?

Is there a guide on here for replacing alternator on here??

 

You want to be reading from the main red cable on the alternator to earth.

 

Your measuring the battery voltage doing it on the body, not the charging voltage.

Edited 18 June by Blue8793841

[huwants2no]

15 minutes ago, Blue8793841 said:

 

You want to be reading from the main red cable on the alternator to earth.

 

Your measuring the battery voltage doing it on the body, not the charging voltage.

There was a black wire held on with nut. And another cable with the usual bag plastic connector. I disconnected it and touched multimeter to one the 2 pins on the alternator and got the reading off that and the metal case as an earth.

Does that make sense:)

[huwants2no]

Can't see 'main red cable' anywhere. Just those two in the pic

[Blue8793841]

Where the black cap is that wire you want to be on

[Blue8793841]

I wouldn't rule out starter motor too, they are common. I've seen people put new aftermarket starter on and have the same fault. Switched to 2nd hand genuine one and it was fine.

[huwants2no]

18 minutes ago, Blue8793841 said:

Where the black cap is that wire you want to be on

Just tested from that and it's between 14.3-14.4 so that seems to be ok.

I think one of those cables running back toward battery was chewed by rat. Just noticed some corrosion. I'll try get a pic

The chewed cable with bit of green corrosion on it is behind front left headlight

Edited 18 June by huwants2no
Add info to pic in post

[pikpilot]

If it looks to you as though water has got into the cable then replace it.

Major sign to look for is the internal multistrand copper conductor turning black.

[Blue8793841]

Doesn't look great. That wire goes from alternator to starter and battery, might be worth replacing the harness to start with.

[huwants2no]

49 minutes ago, pikpilot said:

If it looks to you as though water has got into the cable then replace it.

Major sign to look for is the internal multistrand copper conductor turning black.

The copper wind inside the alternator?

Bloody rats jesus

[huwants2no]

38 minutes ago, Blue8793841 said:

Doesn't look great. That wire goes from alternator to starter and battery, might be worth replacing the harness to start with.

Any ideas as to where I might find a diagram of the wiring?

Thanks for all the replies btw

[JamieH86]

8 hours ago, Blue8793841 said:

I wouldn't rule out starter motor too, they are common. I've seen people put new aftermarket starter on and have the same fault. Switched to 2nd hand genuine one and it was fine.

Yep I would say it is foolish to rule out the starter.

 

I had this issue a few years ago and the starter was the cause.  It was malfunctioning and draining the battery (and ended up ruining it).   Car started fine on leads though, but that is not exactly a long-term solution!

[pikpilot]

10 hours ago, huwants2no said:

The copper wind inside the alternator?

No, I was refering to the chewed cable in the photo.

[huwants2no]

6 hours ago, JamieH86 said:

Yep I would say it is foolish to rule out the starter.

 

I had this issue a few years ago and the starter was the cause.  It was malfunctioning and draining the battery (and ended up ruining it).   Car started fine on leads though, but that is not exactly a long-term solution!

Ok. Why would the starter work grand off jump leads on another cars battery but not work properly off my car battery?

That's what I don't get re starter motor

Thanks

Edited 19 June by huwants2no

[Breezy_Pete]

That alternator output wire doesn't go to the starter motor, it goes direct to the leftmost (as viewed from front of car looking into bay) big vertical fuses at front of engine bay fusebox.

Wire gauge depends on alternator rating fitted, 16mm squared unless it's a 140A alt, then its 25mm sq.  Looking at your earlier pic, it appears to be a 140A alt.

 

 

Edited 19 June by Breezy_Pete

[Breezy_Pete]

SA1 is the fuse it goes to.

[JamieH86]

1 hour ago, huwants2no said:

Ok. Why would the starter work grand off jump leads on another cars battery but not work properly off my car battery?

That's what I don't get re starter motor

Thanks

In my case, the problem with the starter motor wasn't that it was not working in the sense it couldn't start the car, but it had an electrical fault (for more detail track down my mechanic from 2018!) that meant it put too much load on the battery, and the car was progressively harder to start until eventually the battery was flat and all the electrics died one day.

 

However, when starting the motor with jump leads, you're connected to a car where the engine is already running and the battery is charging, so the faulty motor still gets sufficient power to start the engine.

 

Basically the cause of my issue was the starter motor, but the actual symptoms were in my battery.

[huwants2no]

On 19/06/2024 at 13:26, Breezy_Pete said:

That alternator output wire doesn't go to the starter motor, it goes direct to the leftmost (as viewed from front of car looking into bay) big vertical fuses at front of engine bay fusebox.

Wire gauge depends on alternator rating fitted, 16mm squared unless it's a 140A alt, then its 25mm sq.  Looking at your earlier pic, it appears to be a 140A alt.

 

 

Ok thanks for that and the diagram. Whatever it is it's annoying as hell. 330k miles on this girl,maybe time to move on

[huwants2no]

On 19/06/2024 at 13:49, JamieH86 said:

In my case, the problem with the starter motor wasn't that it was not working in the sense it couldn't start the car, but it had an electrical fault (for more detail track down my mechanic from 2018!) that meant it put too much load on the battery, and the car was progressively harder to start until eventually the battery was flat and all the electrics died one day.

 

However, when starting the motor with jump leads, you're connected to a car where the engine is already running and the battery is charging, so the faulty motor still gets sufficient power to start the engine.

 

Basically the cause of my issue was the starter motor, but the actual symptoms were in my battery.

Ah rite. Sorry I wasn't thinking much past the obvious. But I see now there can be other faults but similar battery symptoms

I got a new battery so I'll put that in and see. Will try tidy up the chewed wire as best I can but I guess over time damage will occur along it.

Used to be a great breakers near me where the guy would let you bring tools and remove parts you wanted. Closed down tho sadly

Thanks for the help