Bad Alternator? Voltage drop?

[Bora Sport]

Well it is 16 years old now and over 400,000 kilometres. The battery went flat and an auto electrician told me the alternator wasn't charging enough to stop it from going flat.

[beale187]

So I went home last night, walked down to my VW lawn ornament (spare Bora) and ran a couple of tests on it and came up with this.

Car off, Battery reading: 12.40V
At Idle, Battery reading: 14.40V
At 2,000rpm, Battery reading: 14.28V
At Idle but Under Load: 13.90V
At 2,000rpm and under load (Lights, A/C etc.. all on), reading at battery: 13.80V

All readings substantially higher than my daily drive.

Then i got talking to a buddy here at work who's a LAME and he told me something I didn't know. That is, if a battery has a good resting reading, say of 12.2V - 12.6V it can still fail to produce enough AMPS to crank the starter motor if for example it has a dodgy cell.

Unfortunately my voltmeter does not have the functionality to test / measure CCA (Cold Crank AMPS) for my battery. The Delkor battery I was using (which is 2yrs old) has a CCA rating of 500. So I threw in the SuperCharge Battery from my donor vehicle which is rated 600CCA. Turn the key, car started first time no prob and all the other symptoms disappeared also....

I'll run with that for a couple of days and see how it goes, though I still suspect there more to it than the battery.

[beale187]

Well it is 16 years old now and over 400,000 kilometres. The battery went flat and an auto electrician told me the alternator wasn't charging enough to stop it from going flat.

Holy crap 400,000kms! That's phenomenal, if it gets to 1/2mil I reckon you send it back to Wolfsburg and they can mount it in VW HQ lobby. Incredible.

[Euro Remaps]

I would try making an extra earth lead from the battery to the engine and connect it to the mounting bolt on the starter motor and see if that makes any difference...i spent months with issues relating to possible starter motor,altenator, battery and ignition switch problems that turned out to be the earth lead and its been fine ever since...

[beale187]

Quick update.. Installed another battery with a higher CCA last Friday and have had no issues since. Also removed the battery and tray to check the ground terminals, they were tight but gave them a quick clean up anyways.


But then... Last night driving home I hear an ever so slight "click" noise and my cluster starts flicker and headlights dim. So it definitely sounds like a bad earth somewhere else. I'll pull the front off this weekend and take a look at the cables to alternator.

[beale187]

I would try making an extra earth lead from the battery to the engine and connect it to the mounting bolt on the starter motor and see if that makes any difference...i spent months with issues relating to possible starter motor,altenator, battery and ignition switch problems that turned out to be the earth lead and its been fine ever since...

Funny enough i checked out my donor Bora and the previous owner had done exactly this!

[Bora Sport]

I wait to be proven wrong but it still sounds to me like the alternator isn't charging enough.

[beale187]

I wait to be proven wrong but it still sounds to me like the alternator isn't charging enough.

That's my guess as well... I'm just avoiding jacking it up and pulling the front off to do the job haha, when you live on a hill just jacking it up safely is a pain in the a$$

[beale187]

Quick update.

Since installing another battery there's been no issues starting the beast. However all the other symptoms (cluster flickers, headlights dim when operating windows, humming noise through CD players etc..) are still there.

Pulled the front off over the weekend to get access to the alternator. Hooked up the voltmeter to the B1+ nut on the alternator and the negative post on the battery. At idle and under load (all accessories on) I started with a reading around 14.1v (seemed to fluctuate between 13.8 - 14.2) but it slowly dropped to around 13.3v (I assume this was because the battery had reached full charge?). So I took the rpm up to 3,000 and got a fairly consistent 14.2v reading.

So two quick questions if I can.

Given all readings are around where they need to be is it safe to say the alternator is ok?
AND I have a list of ground points that I need to check around the vehicle, some of which are not easy to access. Can a bad earth in one circuit effect another unrelated circuit? For example; If I have a loose earth connection for a door control module, can this bad earth effect headlights, cluster etc..??

Give me nuts and bolts any day...

[mikk]

Yes, check wiring everywhere. Could it be a short somewhere?