Interior lights on but car wont start
STARTING YOUR DIAGNOSIS
What happens when you attempt to start the engine? If nothing
happens when you turn the key,"http://www.aa1car.com/library/2003/us20310.htm"to
determine its state of charge. Many starters won't do a thing unless there is
at least 10 volts available from the battery. A low battery does not
necessarily mean the battery is the problem, though. The battery may have been
run down by prolonged cranking while trying to start the engine. Or, the
battery's low state of charge may be the result of a charging system problem.
Either way, the battery needs to be recharged and tested.
If the battery is low, the next logical step might be to try
starting the engine with another battery or a charger. If the engine cranks
normally and roars to life, you can assume the problem was a dead battery, or a
charging problem that allowed the battery to run down. If the battery accepts a
charge and tests okay, checking the output of the charging system should help
you identify any problems there.
A "http://www.aa1car.com/library/2002/cm10220.htm" that
is working properly should produce a charging voltage of somewhere around 14
volts at idle with the lights and accessories off. When the engine is first
started, the charging voltage should rise quickly to about two volts above base
battery voltage, then taper off, leveling out at the specified voltage. The
exact charging voltage will vary according to the battery's state of charge,
the load on the electrical system, and temperature. The lower the temperature,
the higher the charging voltage. The higher the temperature, the lower the
charging voltage. The charging range for a typical alternator might be 13.9 to
14.4 volts at 80 degrees F, but increase to 14.9 to 15.8 volts at subzero
If the charging system is not putting out the required voltage, is
it the alternator or the regulator? Full fielding the alternator to bypass the
regulator should tell you if it is working correctly. Or, take the alternator
to a parts store and have it bench tested. If the charging voltage goes up when
the regulator is bypassed, the problem is the regulator (or the engine computer
in the case of computer-regulated systems). If there is no change in output
voltage, the alternator is the culprit.
Many times one or more diodes in the alternator rectifier assembly
will have failed, causing a drop in the unit's output. The alternator will
still produce current, but not enough to keep the battery fully charged. This
type of failure will show up on an oscilloscope as one or more missing humps in
the alternator waveform. Most charging system analyzers can detect this type of
thanks,please rate the solution positively.
Nov 06, 2009 |
1985 Buick Century