On Thu, 22 Jun 1995, Palmer, Lew (UCI) wrote:
> It's the battery - without a doubt. Even though the battery can measure 12
I doubt it, Lew. He has tried two batteries, one of them known good, I
assume by slotting each in turn into the chassis, and neither worked. It
did work when he jumped it. I'll assume he followed good practice when
jump starting, by connecting one jumper cable to the hot terminal of the
battery and the other jumper to the chassis, rather than to the other
battery terminal. If so, the difference between starting and not starting
was that the car started when the current did not have to go from the
battery ground terminal to the chassis. If he applied the ground jumper
to an engine bolt, he also bypassed the engine to chassis ground strap.
Before I bought any more batteries, I would look carefully at the battery
ground connection to the chassis and the engine ground connection to the
chassis. Whether this is a feasible explanation depends a lot on how he
measured the 7.5 volts--across the battery terminals or across the starter
input. If the latter, it is consistent with a high resistance in the
circuit.
Applying my new law, Gibbons's Razor, the true problem is probably
something hideously more expensive than either of us has guessed.
> I am about to complete a three year ground up
restoration of a 51TD. I am > have some trouble starting the rebuilt
engine. Here is the situation: the > battery will not crank the engine,
but it shows 12 volts and all the > accessories and the fuel pump runs;
when I switch on the ignition, the > voltage drops to 7.5 volts; my new
car battery will not crank the TD either; > however, when I jump start it
(i.e., with the engine of the second car > running) the TD starts and runs
fine. > > What is wrong? Any ideas. > > Larry Swift
>
Ray Gibbons Dept. of Molecular Physiology & Biophysics
Univ. of Vermont College of Medicine, Burlington, VT
gibbons@northpole.med.uvm.edu (802) 656-8910
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