by "acarr260" (acarr2601)
Published 10/18/2017 at 10:31
by "acarr260" (acarr2601)
Published 10/18/2017 at 10:31
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A couple of weeks ago, the battery light started coming on in my Scirocco. It got slowly worse until the battery died. I jumped it, but it didn’t stay running for very long. I then put in a new battery. The light persisted, so I had the alternator tested. With the car running, it was putting out 11.83 volts. It should be putting out 13.5-15 volts while running. I then ordered a new alternator. I installed it last night, and the battery light is on even brighter now. What else should I look into? I’m trying to avoid taking it to a mechanic, because that could result in a lot of billable hours trying to chase down the issue. Thanks!
"kanadanmajava1" (kanadanmajava1)
10/18/2017 at 10:37, STARS: 3
A grounding issue? Try measuring the voltage (while the engine is running) between the battery negative terminal and the alternator frame.
"diplodicus" (diplodicus)
10/18/2017 at 10:39, STARS: 1
Did you recheck output voltage for the new alternator? Make sure the terminals on the wire aren’t corroded and everythings tight.
ETA: Is the belt properly tensioned? If it’s slipping it would result in lower output.
"merged-5876237249235911857-hrw8uc" (merged-5876237249235911857-hrw8uc)
10/18/2017 at 10:41, STARS: 0
Shouldn’t that value be 0? And 0 ohms resistance as well? Both those sources should be grounded, correct?
"kanadanmajava1" (kanadanmajava1)
10/18/2017 at 10:45, STARS: 2
It should be zero if alternator is grounded to the engine and the engine to the chassis/battery. But the wiring can get corroded. If the grounding wires fail completely the grounding can go through the driveline bearings which is lethal to them.
My Opel had a separate ground wire from the alternator frame to the engine as the mounting was isolated with rubber bushings.
"merged-5876237249235911857-hrw8uc" (merged-5876237249235911857-hrw8uc)
10/18/2017 at 10:46, STARS: 0
What is the voltage of the new alternator when the car is running? Just measure voltage across the two battery terminals while the car is running. Should be greater than 12 volts. Also have the new battery charged and tested. If the old alternator was weak, the new battery may have been drained down as well. But you should retest it to make sure all the cells are functioning correctly. That coupled with the alternator voltage check, and the ground check that was suggested by kanada, should tell you where the magic pixies are escaping the charging system.
"deekster_caddy" (deekster_caddy)
10/18/2017 at 10:52, STARS: 1
Does the sirocco have an internal voltage regulator or external? It’s possible the new alternator has a bad regulator, wouldn’t be the first time. But if it’s external, check that out...
"merged-5876237249235911857-hrw8uc" (merged-5876237249235911857-hrw8uc)
10/18/2017 at 10:57, STARS: 0
Cool, learned something new. And since the alternator is providing the charge, the ground between the two is what you want to check correct? Should resistance be 0 as well? Or near zero? So if the ground is bad, what voltage value should he be seeing as he’s doing the check? Oh, maybe I’m thinking of continuity, because assumeing the ground is good, there should be continuity between the alternator frame and the battery ground, correct? And assuming there is, you would want the resistance to be as near 0 as possible, right? That means the ground is good? Because if you have continuity but high resistance, that would lead me to believe there is a bad connection to ground, either from the battery ground cable, or the alternator/engine ground.
I’ve never really had to diagnose one like this, hence my questions, anytime I’ve had a bad ground it was obvious, as in severed wires or loose terminals. So this is good info to know.
"kanadanmajava1" (kanadanmajava1)
10/18/2017 at 11:05, STARS: 1
The resistance should also be near zero, but sometimes this cannot be measured correctly without any load.
"merged-5876237249235911857-hrw8uc" (merged-5876237249235911857-hrw8uc)
10/18/2017 at 11:08, STARS: 0
Gotcha. Good stuff to know.
"brianbrannon" (brianbrannon)
10/18/2017 at 21:12, STARS: 0
Battery cables can also prevent charging the battery. Check the voltage at the alternator terminal with it running
"acarr260" (acarr2601)
10/19/2017 at 10:17, STARS: 0
My Scirocco has a ground wire running from the alternator to the engine as well. When I replaced the alternator, I noticed that one of the rubber bushings where the alternator mounts to the engine was pretty worn down. Would that cause the issue?
"kanadanmajava1" (kanadanmajava1)
10/19/2017 at 10:29, STARS: 0
If the wires are ok and the belt doesn’t slip it shouldn’t affect the charging performance at all.