Date: Sun, 11 Sep 2016 22:07:30 -0700
Reply-To: Christophe Guilbert <cguilbert@PICASSO.UCSF.EDU>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Christophe Guilbert <cguilbert@PICASSO.UCSF.EDU>
Subject: Engine Ground voltage drop under load, please help diagnose.
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I have a vanagon 1983 air-cool CA.
I would really appreciate some help to diagnose my problem , even my
mechanic does not understand it.
Here is the story:
My battery is new and read 12.6v . I have a new alternator which deliver 14V
When the van idle I read 13.71V at the battery terminal. When I start
lights and fan blower , I read 13.24V.
I tried to check if I had any leak between the battery terminal and the
alternator under load (lights and fan blower):
For terminal + , I have none , well something like -0.1V
For terminal - , not only I have -0.5V at the alternator level but also
to any ground point of the engine, which is way too much ! ( I have
-0.1V only if I am not under load)
In order to remind how the engine is grounded , here is the pathway ,
from battery to the body using a ground strap , than from body to
transmission front mounting using a ground strap, than from
transmission front mounting to the transmission via metal contact and/or
3 bolts and stud. than from transmission to the whole engine.
Trying to understand where my 0.5v drops come from , I checked if I had
any voltage drop between the battery ground terminal and the ground
strap terminal bolted to the transmission front mounting . I have none
(-0.04v) . So voltage drop must happened between the transmission front
mounting and the transmission or the engine. I plugged my voltmeter
between the ground strap terminal going to the transmission front
mounting and the engine (any points) and I found -0.45V.
When I plugged my voltmeter between the ground strap terminal going to
the transmission front mounting bolt and one of the transmission bolt
(after making it bare metal), I got -0.35V. So the main culprit seems to
be the connection between the transmission front mounting and the
transmission itself. I removed the transmission front mounting , clean
bolts ,studs, washers, any point of contacts, I make them bare metal,
used deoxit D5 and di-electric grease before putting every back. I
retest the ground voltage between the battery and the engine and I got
-0.4V (instead of -0.5V) under load.
From this point I don't know what to do and would appreciate any
explanation and advices.
I am thinking to reground the engine . If I quickly used a jump start
cable to reground the engine , I reduce my voltage drop from -0.4V to
-0.2V. I guess I can do better with a proper dedicated ground cable .
I would rather avoid that option thought because I would like to fully
understand what's going on first.
Any though.
Thanks for any help.
Chris