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Electrical: Engine Starting, Charging
(exide cro-guard, etc)? removed the starter B+ (positive cable) and brush the lug
and the stud it attaches to plus all washers and mounting points. retightend and
apply antiC? Same applies to ground connections. [Editor] For years, I have used
the little colored fabric washers (red/green) that go under the battery terminals to
prevent corrosion. They really do work, especially when combined with an anti-
corrosion spray (the little cans of red spray you can buy at Walmart). Never, ever
had a corroded battery terminal or wire set.
Diagnosing Corroded or Malfunctioning Cables and Wiring Using the
"Voltage Drop" Method:
[Motor Magazine Mar 04] Measuring the resistance from one end of the cable (the
battery) to the other end (the starter) will not reveal a problem. That's because
your Digital MultiMeter places an almost unmeasurable load on the cable when it
measures its resistance. Because the load is so small, the DMM will show a very
low resistance reading, as long as even just a few of the strands in the battery
cable are still good. The DMM can't tell the difference between a good cable and a
bad one with this test. What's needed is a test that will reveal the cable's
performance when it's in operation and under a load. To test the negative battery
cable, attach the DMM's negative lead to the negative battery terminal. Don't
attach it to the terminal clamp; we want to test the whole circuit from end to end.
Attach the positive DMM lead to the starter motor body or the engine block. Set the
DMM to the 0-40 volt DC scale, then have an assistant crank the engine while you
watch the DMM display. Any voltage reading shown represents the voltage that has
been dropped between the battery and the starter motor. Typically, a ground cable
that's in good condition will drop .1 volt or less. Don't accept a voltage drop that's
greater than .3 volt. A cable that's causing starting problems may be dropping far
more than even these modest amounts. Voltage drops may occur at any point in a
circuit. It may not be practical to replace all of the suspect wiring, so it will be
necessary to pinpoint exactly where the voltage drop is occurring. It's relatively
easy with something like a battery cable because there are only a few joints or
connections in the circuit. If there's a voltage drop, the likely suspects are the cable
itself or the terminals at each end. Cleaning the connections and replacing the
cable should take care of the problem.
When a circuit is longer and more complicated than a battery cable, save time and
keep your diagnosis focused by using the split half method. Divide the circuit in
half, then perform a voltage drop test on one half at a time. Find a convenient
connector somewhere in the middle of the circuit to mark your halfway point.
Conduct a voltage drop test on the front half of the circuit while it's under load. If
no significant voltage drop is found, move to the rear half of the circuit, then
retest. Keep dividing the remaining segments of the circuit in half until you've
narrowed it down and have conclusively located the voltage drop. Many circuits on
today's vehicles are designed to carry very low voltage and amperage. Ohm's Law
reminds us that any added resistance in these circuits will have a direct effect on
their ability to perform as designed. Voltage drops measured in tenths or even
hundredths of a volt can be significant and will cause problems.
Cleaning Battery Posts and Connectors:
[Editor] You can clean the battery posts and cable connectors safely by:
file:///C|/Users/Steve/Documents/Volvo%20FAQ%20Updated/ElectricalStarting.html[01/13/14 10:02:47 PM]
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