charging system ????

timbradley26 · 11-15-2009, 07:06 PM

i have installed a new bat. and alt. i get a reading of 3.8 at the bat when running . but when i turn it off i get a no start. i connect a bat charger and she will start . does that mean my new bat could be bad or is there something else i am missing help

timbradley26 · 11-15-2009, 07:07 PM

sorry it should read 13.8

81c3 · 11-15-2009, 09:53 PM

Voltage sounds crrect to me. The no start sounds like a bad connection somewhere. Why did you replace the battery and alternator to begin with.

timbradley26 · 11-16-2009, 12:17 AM

i was cking the charging system on this car . just bought it and it had sat in a barn for 5yrs. needed a new bat . when i cked the voltage with the car running it was 13.2 which i knew wasnt right .plus the alt was a little noisy. i pulled the plenum and did new coils ,wires and cked all the secondary vac system so i fugured while i was at it just replaced the alt. too .

Paul Workman · 11-16-2009, 05:41 AM

A fully charged and warm battery will have about 13.6-8 volts across the terminals, if the alt is charging correctly. 13.2 or on a new battery and -
1) either the battery is severely discharged (put a charger on it and after it is charged, start it and re-measure and see if it isn't up around 14.7 initially)
2) the regulator is bad, OR there is a connection issue either with the field coil connection (that little plug on the back of the alt) or there could be a ground issue.

Gotta run, but the FSM and a VOM will point you to a connection issue. My guess is the voltage reg.

P.

81c3 · 11-16-2009, 05:07 PM

13.8 is perfectly normal for a voltage reading across the battery terminals if the battery is in good shape. The alternator wont need to raise the voltage via the field coil if the battery is healthy. A fully charged battery reads 12.4 to 12.7 when sitting on the bench. If the battery is new, the charging system wont bump it up hardly at all, especially if theres no current draw.

When the engine is running, pull on the headlights and switch on some accessories, see if the voltage increases. If it does, the alternator is charging properly.

I would bet on a bad cable connection at the starter terminal now that you say you had the plenum off and was under there dinkin' around....or a bad battery cable connection either at the + or - terminal. Also check the 12V feed wire on the back of the alternator and see if its tight as well as the purple wire to the starter itself.

timbradley26 · 11-16-2009, 05:33 PM

thanx for all the help guys i will ck it all after dinner