[T2] Engine Ground voltage drop under load, please help diagnose.
Christophe Guilbert cguilbert69 at gmail.comSun Sep 11 22:04:48 PDT 2016
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Hi guys. 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
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