puzzling alternator / charging problem MK1 Scirocco 1.7L gas

[tannere]

Hi all, I have a charging problem, I Hope you can help!

I have a 1981 MK1 Scirocco with the 1.7L gasoline engine and bosch alternator w/ integrated/internal voltage regulator.


The main issue is that the alternator is only putting out 13V while the engine is running, not the 14.5V that it should, even though the alternator is newly refurbished. There is also some sort of parasitic drain on the battery while the car is turned off, approx. 1V loss per day (may or may not be related). Here are the readings and recent work:


- Newly refurbished alternator. It was told it now puts out 14V+ and the integral voltage regulator was checked out and is good

- brand new battery

- engine running, alternator puts out 13V

- 2 large prongs on the alternator connection test at 11.6V with the engine off

- 1 small prong on the alternator connection tests at 11.6V when the key is turned

- Alternator ground connection checks out good as well



Any thoughts? I covered the basics and what is described in the manual, and left confused.



Thanks!

[chopperoli]

What was the voltage before the alternator swap? Maybe it's a bad refurb, or a bad regulator

[EDDIE-F]

Sounds like the earthing strap from engine mount to body to battery negative has gone high resistance. maybe try clamping a black jump lead from engine block to battery negative. see if you get aprox 14 v on the battery to charge it on a fast tickover.

[james butler]

the brush packs can be a problem to source the correct type (I've seen at least 3 types for different amperage types)
do your basic checks first like the earth points especially where the alternator bolts to the engine block and the return from block to battery
then all the live cables
is your battery ok? old batteries can pull the voltage down when on their last legs
to find your parasitic drain get yourself an ammeter, with everything turned off remove the live terminal and connect the meter to the live terminal and the other side of the ammeter to the battery live post
this should show you the current flowing out of the battery with everything off (this should be no higher than 0.3amps for the clock and whatever)
if its higher than this which it sounds like it is you have a parasitic drain.
to find it, start pulling fuses out of the fuse box one at a time and watch the ammeter.
if you pull a fuse and the ammeter drops that fuse is the circuit that has your parasitic drain.
I've had a couple over the years and this is how i found them.

[tannere]

Yes I am starting to question the refurb job. I will go through the steps recommended above for the ground connections first before pulling the unit out and taking it back. The battery is brand new.

Thanks for your tips!

[mark1gls]

Boot light, aftermarket alarm or immobiliser are a common source of battery drain.

[tannere]

Update: She's back in action! Thanks for all your advice. Turns out, there were a couple bad ground connections, and the parasitic drain was coming from the radio. I pulled the fuse on the radio to eliminate that and will investigate that further. But in the meantime, glad to have the car back on the road.

[mark1gls]

Glad to hear it’s all working again

[james butler]

good to hear you found the issue
radios sometimes HAVE to be wired one permenant live for memory and the other MUST be switched live from the igntion.
if you wire the switched live to the battery you will find the radio is never trully off and drains the battery.
at least thats the problem i had with my alpine