Battery Voltage Issue

[selym]

Ok, so I changed my water pump and belts at the same time, and removed the battery for access. This is a newish battery. Ever since, my voltmeter shows the battery voltage going up and down between 12v and 13.5v engine speed dependant, dropping to 12v when throttling off. Switching on the lights causes a slight drop.
I also use Torque Pro to monitor the voltages; I have two showing, one is OBD port voltage and the other is system voltage. I have 13.9v dropping to 13.6v when the battery has been charging for a bit (system voltage) and the OBD voltage pretty much mirrors what the voltmeter is showing. I get a check engine warning but no stored code or engine light on the dash shortly after setting off - I think the odd voltage issues are causing it.
I've cleaned the terminals and they look fine, and I have a solid 12.8v at the battery when off, and 14v at the battery when running.

Sorry for the long post, I think I have all the symptoms there - any ideas?

Cheers,

Myles

[stevieturbo]

And was it doing that before ?

[selym]

stevieturbo said:

And was it doing that before ?

Nope!

[vxr2010]

Poor earth connection on battery terminals or a bad positive connection ? i put a second earth on all cars i have as it can be a bit of an issue

[selym]

vxr2010 said:

Poor earth connection on battery terminals or a bad positive connection ? i put a second earth on all cars i have as it can be a bit of an issue

What is an easy way to check for that? I've measured from the earth wire on the block to the earth on the strut turret, which seemed ok at 5 ohms. Perhaps I need to investigate further afield to the alternator connections? It's the voltage dropping off when I throttle off that is odd.

[stevieturbo]

5 Ohms sounds like a lot, it really should be almost zero.

But it must be something you've disturbed during works, whether wiring, maybe new belt not tight enough or something

[selym]

stevieturbo said:

5 Ohms sounds like a lot, it really should be almost zero.

But it must be something you've disturbed during works, whether wiring, maybe new belt not tight enough or something

I think you may be right on both counts. I'm going to check belt tension and give it a little extra tension with a spanner while an oppo revs it - see if that makes any difference. The proof of the pudding is in the driving so if I can tension the belt much more by hand then the tensioner might be tired.....
I need to buzz out all the wiring, but need to be certain what is connected to what.