Why does the voltage drop to battry volts when i put the gear lever in drive?
1979 ford thunderbird 8 cylinder when i stsrt the engine up the charging system show 13.9 to 14.1 volts sometime at idle with no load when i turn the headlights on and heater on high the volt is 13.9 but when i put the gear lever in reverse or drive the volts drop down to 12.2 volts why do the volts drop to 12.2 volts? what is the voltage range at idle and when a load is on?
Cars & Trucks - Ford
Answers & Comments
The voltage should remain at 14.5 volts at all engine speeds above idle 13.9 volts at idle indicates that the alternator is charging but not at set voltage
head lights are the biggest drain that affects charge rate rate and it it maintains and from you description that is not a problem
when you select a gear it indicates a heavy drain which is a high resistance or a dead short in that circuit that is taking out more power than the alternator is charging
There there is nothing in the gear selection that draws such power
the other thing is that when selection a gear the engine rpm is tool low and the alternator stops charging
for auto vehicles , the idle rpm should be at 800-900 rpm dropping to 750-800 in drive
raise the idle speed to around the 850-900 mark
full regulator voltage control comes it around 2,000rpm but voltage drops back to 13.2 volts as the battery reaches fully charge point
do i need a special tool to raise the idle speed to 850-900 how do i know when the RPM is where it should be?