My friend has a 93Z LT1 and he has an altenator that is a year and 1/2 old his voltage runs just below the half way mark on the gauge so he bought a new one and it does the same thing,he complains that when the car warms up the voltage will drop, he has checked all the wires under the hood and the grounds, when he first starts the car the voltage is 14.1 and as it warms up it drops to 12. Is this normal are not? Any suggestions?
Thanks

 

Where are you measuring the voltage? Not the gauge in the dash, I hope. Put the meter on the battery with the car running & warmed up and also check it on the alternator and they should be similar, hopefully around 13.8 or so.

 

He checked it with the car running (warm) with a volt meter at the battery 12.4 when he starts the car the first few minutes its high 13s low 14 it seems that when it warms up the voltage drops.

 

maybe you have a bad ground or battery cable.

 

I have checked all the cables and grounds
Would an underdrive pulley cause this? He also has an overdrive ALT pulley.

 

I had a similar problem a couple days ago. It turned out that one of my alternator bolts had backed out, and tensioner was a little loose. Tightened them both and voltage was back to normal.

 

doesn't the voltage drop when the car is warm becuase the battery no longer needs as much charge.

ex. car is sitting for a few days the battery is weak so the voltage regulator puts more voltage to charge the battery, once its full the regulator cuts back the voltage.

i know my car reads high and goes low when its hot....13.1 is what it is after driving for 10 mins.

 

Measure the alternator by puting the DMM probes on the Batt connection on the back of it and the alternator body as a ground. If it isn't over 13.8 at high idle, then something might be wrong with the alternator. If there's too much drain and it can't keep up, that's a different matter. Anyhow. measure the voltage drops on all the cables and they should be less than .5V (I like a lot lower than that). Any more than that and you have bad cables or bad connections. Measure the alternator case to engine ground and also to the ground stud on the fender. Make sure there are no big drops again. The battery voltage should never be lower than 12.8 except during cranking - if it is less than 12.6, then it is discharging (and you don't want that). Ideally, you should have 13.8-14 at the battery with a healthy alternator with the right pulleys, good battery, good cables & connections. Good cables & good connections = low voltage drops.

FWIW, I had a similar problem on a clean car - all good parts - I ran an extra ground cable from my alternator bracket to the ground stud and that brought up the voltage on the gauge to where it should be.

 

i have UD pullies but i'll bring the rpms up to 2000 and the voltages just stays around 13.1


convinced my alt was bad i went over to check my dads truck...2001 silverado

2000 rpm, 13.1 volts.

i guess im cool.

 

Mine goes down to 9 when its REALLY hot, like 110* or so. Anyone want to take a wild guess which one will fail first, the alternator or the battery LOL. Its cuz of my underdrive crank pulley, but i tried fixing it with the overdrive alternator pulley and it barely helped, if any...

Sorry to hijack the thread, but would a higher output alternator fix my problem?

 

this is prob a dead thread anyway :-P


but 9

i've got the 45% reduction pulley with no overdrive and it only goes down to 12.8 at idle.

it jumpes up pretty quick when it gets around 1000 though, i've never had a charging problem or anything.


but like i said before once its been running for 10 mins or so my alt doesn't feed the battery more then 13.1

 

ok so i havn't driven my car since friday...i test the battery after sitting and its 12.2 hmm
ok i crank the car up...the volts gauge is rigth at the red for 2 seconds.....then you see it set up to above the middle line.

i read the voltage and it was 14.2 at idle

this was cause the batt was low and needed some charge, i ran it for 15 or 20 seconds shut it off...battery was already at 12.6

if anything I should probably get a badass battery since i let my car sit all week without being driven.

 

well mine jumps to 13-14 when its above 900rpms, but at idle it goes down to 8-9 on a 100*+ day...

 

just now is the 1st time i have saw my alt put out 14+ on the mulit meter LOL


what kinda UD pulley do you have?? 8 and 9 is WAYYYYYYYYYYYY to low. is your gauge parked in the red at idle?

 

I get the same thing with my car. On a hot day when the fans are running a lot the voltmeter will read just below the middle line and as I cruise more the meter will slowly rise. IMO it is a heat issue with the alternator and its wiring (as temperature increases so does resistance).