Leland Pate

My car has developed a problem with battery voltage in the past few weeks. I started noticing it was cranking slower and slower. I also noticed my battery light on the gauge panel was glowing faintly. Finally I realized it was not the cold weather and that something was wrong because the cranking got slower and the batt. light got brighter. I checked the battery voltage with the engine off and got something like 11.79v. With the car running I got ~12.86v.

I thought the alternator should be pumping out about 14+v's.

I took the battery to the store where it was bought and ran a dignostic on it. They say the battery is fine.

So I've got a current draw somewhere or an alternator that is not alternating. I replaced the alternator less than a year ago when the old one failed at the track. The battery is also about 13 months old.

What could be the culprit here? A few guys at work said the starter could be the problem.
Any ideas how to proceed with the diagnosis?
_________________________________________
Is there a good way to test the alternator output?

Is there a method to tracking down current draws?

TIA,
Lee

kkim

If you disconnect the battery, what does the voltage read? If the battery is good, it should read a bit over 13v.

My guess is bad battery or a dying one. Do you have another handy that you could try for testing purposes?

Leland Pate

I just tried it again.
With the motor running I am only getting between 12.4 to 12.6 volts from the cigarette lighter. When I rev the engine it seems to drop the voltage. The lowest it got was 12.3v.

Something is not right here.

kkim

What is the batt voltage w/ it disconnected from the car?

Traffic53

let me guess...is it one of those optima batteries? if i recall correctly, our systems charge a bit lower than say, a domestic. they top up at 13.6-13.8...something like that. so if i'm understanding it right, the battery we choose should be one that's happy when fully charged at that level- which the beloved optimas are not. i think those, and some other maintenance-free units like to be mated with electrical systems that get up to 14.4-14.6 or so. when those batteries aren't fully charged- and they will never be in our cars, they tend to have some of the pre-mature death stuff that's been reported here when the car sits for more than a week. then again, i could be wrong about all of this.

Leland Pate

Kkim, disconnected it only goes up 100th of a volt. from like 11.68 to 11.70v.
Mike, this is just a plain ol' exide battery.

Doesn't it sound like the alternator is not chargine enough?

sidned

Is there a drain when the engine is turned off? A simple way to check is to test the current being passed by holding a volt meter (or a couple of pieces of wire with a bulb in the middle - use insulating pliers) between the negative terminal of the battery and a ground on the vehicle. If there is a high current (there will be some current due to the clock, immobiliser etc) you can isolate it by removing fuses one by one until the light goes out.

It's a bit of a long shot but this is how I found a stuck window switch on an old car I used to own.

Ron

Check this thread, https://rennlist.com/forums/showthre...ighlight=drain, it may have some information that will be helpful to you in accessing your situation.

Red rooster

With the motor running the alternator output should be between 13.8 and 14.4 volts measured directly at the battery.Dont waste time checking voltage at the cigar socket etc.
If you dont have that , the battery isnt being charged !

Your numbers ( 12.86 volts ) confirm it isnt being charged so it is either voltage drop between the alternator and battery OR that new alternator has failed !!!!!
I would hook a substitute battery on just to confirm this situation .

Was the replacement alternator new OE or an exchange rebuilt ?

All the best

Geoff

Leland Pate

Geoff, it was a rebuilt Bosch unit. I spoke to Steve W. this mornng and he believes I have a bad voltage regulator. He's sending me another one so I'll swap it out. Hopefully this fixes the problem.

Red rooster

I would agree 100% . Good luck with the replacement but do check the running ,charging volts !!

Good luck

Geoff

Tom Pepper

Leland,
Experienced pretty much your exact scenario this week. Ended up reluctantly towing the car to my tech who ran similar diagnostics.
I am betting it is the alternator, as that was my problem. Alternator and belts plus labor was 500 bucks.

Good luck.

It's risky betting against Steve, so I'll hope I am wrong and that you get the cheaper option.

Leland Pate

Well, my father would smack me upside the head if he were still alive.
"ALWAYS" check the easiest items first.

Problem solved. It was the hot lead to the starter motor. It had worked its way loose. Now I'm charging at 13.7 v at idle. Car fired right up.
Just thought I'd post this for the archives.
Thank you all for your help.

Tom Pepper

Great.
Now you can leave the Bosch stickers on your avatar