3FE Alternator Not Keeping Up.

[markdrm1]

I've seen some posts about this issue but most seem to be pretty old. Can anyone shed some light on my 91 LC alternator dilemma?
Situation in a nutshell: Battery charged to 12.8 volts last night while hooked to a charger. At that point the alt was charging at 14 with no accessories on. Drove to work this morning without problems and then started fine at lunch. Drove about 4 miles and then idled with AC on for about 20 minutes. Decided to put volt meter on it after I shut it off and the battery read 12.00 volts. I've had the denso checked at two different auto parts stores and both said its good. Belts are tight and in good shape. Cables connections appear secure. Not really wanting to spring for a high output alt right now but wondering if it's my only option. Am I missing any details? Thanks

 

[Tools R Us]

Battery age/condition?

 

[jdayment]

since your reading the battery have you verified the battery is good?

 

[markdrm1]

Sorry, yes, battery newish and tested good the other day.

 

[inkpot]

Parasitic draw?

 

[izzymonkey]

What is your problem with the truck? what do you mean not keeping up?

 

[markdrm1]

What is your problem with the truck? what do you mean not keeping up?

Battery drain.

 

[Tools R Us]

A couple more tests:

... Battery charged to 12.8 volts last night while hooked to a charger. ...

Fully charge, remove the charger, allow ~hour rest, what is the battery voltage?

... At that point the alt was charging at 14 with no accessories on. ...

Start, turn on everything, A/C max, doors open, high beams, etc, voltage check, raise engine rpm to ~2000, voltage check? Both checks at the battery.

... Not really wanting to spring for a high output alt right now but wondering if it's my only option. Am I missing any details? Thanks

Unless you have a ton of aftermarket junk running all of the time, the factory alt should be more than enough, by a large margin. The big white charge wire has been known to occasionally be a problem. At the alt, wire strands broken, connection bad, etc, or at the fusible link, connection or link bad.

 

[markdrm1]

Thanks @Tools R Us , I will give it shot tomorrow and report back.

 

[izzymonkey]

Check batt with nothing on after a full charge. Or take it to auto zone they'll be able to quick test.
If batt is good start truck. at idle test voltage output from batt. Should be at least 12.8v. One by one turn on accessories and checking voltage at battery in between. when it drops below 12v check voltage output at alternator itself they are different it's wiring, if it's same alt is most likely bad.

 

[LAMBCRUSHER]

gotta be careful with your local FLAPS...mine told me my alt was good at 13.4 volts; they couldn't say jack about amps. By fsm specs, 13.4 is bad; wanna say it was supposed to be 13.6 or 13.8 by Toyota spec...the elcheepo otto parts houses keep lower specs so they don't have to warranty their junk. take it off the truck and take it to the old dingy warehouse by the airport that say ELECTRIC MOTORS out front and nothing else- that guy will set you straight.

 

[LAMBCRUSHER]

and keep a spare. they always go out on a thursday and leave you stranded till Tuesday. mine spare is in a box by my bed. It is a new aftermarket unit. I am told the windings are no longer available. hopefully my spare is good enough for Murphy.

 

[izzymonkey]

.

 

[catfishhands]

******* it @LAMBCRUSHER my alternator went out yesterday- and you know what that day was?

 

[LAMBCRUSHER]

Not tryin to say I told ya so... that sucks... try your local flaps- you might get lucky...

 

[LAMBCRUSHER]

Friendly local auto parts store- f l a p s