Welcome to Just Commodores, a site specifically designed for all people who share the same passion as yourself.

New Posts Contact us

Just Commodores Forum Community

It takes just a moment to join our fantastic community

Register

Mystery V8 charging issue

Deuce

Super Stock
Joined
Feb 5, 2012
Messages
3,111
Reaction score
1,995
Points
113
Location
Snobs Rock (or so the locals say)
Members Ride
'94 VR SS V8
My car is strangely not charging correctly. Anyone got some ideas?

Scenario:
94 V8 SS running fine for about 450km's of 500km trip.
Stop in to visit people about 30km from home. Upon departing their home, notice my battery warning light is on (after traveling a few km's with everything electrical on). Also notice that the voltage read out on my head unit is down around 2Volt from where it normally sits. (11.8 down from 13.8-14.2). I checked I hadn't thrown an alternator belt, and then continued on home.
Testing:
checked all fuses (fine), removed battery, checked water level of every cell (maintenance free but had caps??), cleaned terminals, refitted battery (trickle charged for 30min), checked alternator belt deflection (approx 12mm), removed alternator plug (it was clean) electrical lubed and refitted. Started and was charging fine. 14.6volt output at alternator power lead, 14-14.2 on head unit display, 14.4ish across battery.
Drove to servo for some gas (fine), 400m to the supermarket (fine), start up to drive home - issue rears it's ugly head again. Got home, checked alt power wire, and output is at 12.2volt, so is battery and head unit display.

Car is now on trickle charger and I will pull down and examine my spare alternator before putting that in (condition unknown).
If any one has had a similar issue, or can recommend something to check please let me know.
 

K-BAGZ

De Plane! De Plane!
Joined
Dec 22, 2012
Messages
524
Reaction score
12
Points
0
Location
Far North QLD
Members Ride
VR II S-pac V6 Ute / VZ SV6 Sedan / VZ R8
Checked specific gravity of each cell?

Maybe a diode has failed in the rectifier bridge, reducing alternator charge output.

How hot does the alternator get? Checked the B+ terminal tightness?
 

K-BAGZ

De Plane! De Plane!
Joined
Dec 22, 2012
Messages
524
Reaction score
12
Points
0
Location
Far North QLD
Members Ride
VR II S-pac V6 Ute / VZ SV6 Sedan / VZ R8
Checked specific gravity of each cell?

Maybe a diode has failed in the rectifier bridge, reducing alternator charge output.

How hot does the alternator get? Checked the B+ terminal tightness?
 

Deuce

Super Stock
Joined
Feb 5, 2012
Messages
3,111
Reaction score
1,995
Points
113
Location
Snobs Rock (or so the locals say)
Members Ride
'94 VR SS V8
Checked specific gravity of each cell?
Maybe a diode has failed in the rectifier bridge, reducing alternator charge output.
How hot does the alternator get? Checked the B+ terminal tightness?
Haven't checked gravity, but quite confident the battery is not the issue (only 13months old and a good brand)
Yeah I thought the diode bridge may have been at fault, so was going to chuck my spare alternator on if it appears all good.
The alternator did not seem excessively warm compared to other components of the engine bay. ahh good thinking, I will check that.
 

BlackVXGTS

Well-Known Member
Joined
Aug 14, 2004
Messages
4,471
Reaction score
1,195
Points
113
Location
Melbourne, SE
Members Ride
GEN-F2 GTS A6, VS Clubsport 185 A4
The problem could be the voltage regulator in your alternator. The bushes wear out over time and you can start getting the battery light coming on intermittently or full on. Easy and (relatively) cheap to replace - $35 for a new Bosch unit on eBay.
 

Deuce

Super Stock
Joined
Feb 5, 2012
Messages
3,111
Reaction score
1,995
Points
113
Location
Snobs Rock (or so the locals say)
Members Ride
'94 VR SS V8
Update:
wire brushed, sanded, lubed and refitted B+ terminal (It was done up, but not super tight) also done the same on D+ terminal.
refitted battery negative terminal and found that when fully tightened - it could still slightly rotate on negative post. Modified terminal and refitted so it holds tight.
I'll give the battery a little longer to trickle up and then see if that has made any difference.

Also:
V/R brushes on spare alternator look close to the end of there service life, so it will get any parts before I look at fitting it.
 

Deuce

Super Stock
Joined
Feb 5, 2012
Messages
3,111
Reaction score
1,995
Points
113
Location
Snobs Rock (or so the locals say)
Members Ride
'94 VR SS V8
Started it up and now have 14.4 @ B+, 14.3 across battery, and 14.2 (maximum) at head unit.
It seems all is fixed for now. although, may hurray with my spare alternator rebuild just in case.
thanks for the ideas guys. (i'll keep you posted if the issue comes up again)
 

drewVHSS

Donating Member
Joined
Apr 1, 2010
Messages
713
Reaction score
6
Points
18
Location
Gosford Central Coast
Website
stores.ebay.com.au
Members Ride
'83 VH SS, '79 Green VB SL '92 S2 VQ Caprice
main charging cable from alternator to battery, common issue is for the insulation to get brittle and break away leaving the cable exposed.
When the cable heats up from the engine and heat from resistance in the cabling, the main charge cable can break contact and fail to feed power from teh alternator to the battery.

Run a new cable or add in an extra one in parallel to the original one.
 

bsb84

Member
Joined
Jun 5, 2009
Messages
45
Reaction score
0
Points
6
Location
sunshine coast
Members Ride
5L vs ute
as BlackVXGTS said, i had same problem recently, bought new voltage regulator think was bout $40, thought worth a shot being alot cheaper then alternator new or reco, installed it and all good
 
Top