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-   -   Ever seen an alternator fail like this? No charge, no battery light. Metro problem of the month! SOLVED! (

MetroMPG 10-31-2019 06:09 PM

Ever seen an alternator fail like this? No charge, no battery light. Metro problem of the month! SOLVED!
I've had my winter beater Metro on the road for less than a week, and it's already sprouted a new exhaust leak and developed a charging problem! Awesome!

Let's talk about the charging problem - I've never seen one like this before.


- Sometimes when I start the engine, the alternator is not charging. But sometimes it is (but much more likely not).

- On the more rare occasions it is working, if I do an engine-off coast, it may not resume charging the next time the engine is started. Alternator run time doesn't seem to change the odds that it will continue working on the next start-up.

The bizarre thing:

There's NO battery warning light showing on the dash when the alt is off but the engine is running. But it does show when the engine is off and the key is in the run position.

Because of that lack of warning, I first discovered the problem when the car radio blinked off (while driving - 100 km round trip). And when I next went to use the starter... nada. Battery voltage showed 7v! Battricide! Odd how the engine seemed to run well enough at that voltage, but the radio said "nuh-uh!"

I haven't done any kind of testing yet.

I'll check battery connections - but I don't think that would explain the lack of idiot light. Also, the engine fires right up when I turn the key (assuming 12+v SOC).

I will probably just swap the alternator with a known good one, but I'm not confident that's the problem. I've seen more than a few alternator failures in my life, but have never heard of an intermittent failure or a failure with NO idiot light warning.

redpoint5 10-31-2019 06:19 PM

Maybe idiot light only comes on at some lower voltage; lower than standard battery voltage?

Strange issue. I'd expect some loose connection based on the description.

2000mc 10-31-2019 07:38 PM

Last time the alternator died on my Saturn it didnt turn on the battery light. When I noticed it I had been driving for about 5 minutes, and first symptom I noticed was rather odd. Id set my cruise control, and 2 seconds later it disengaged. Did that about 3 times and started looking at my gauges, noticed my scangauge said 12.6, so I turned around and went back home. If I turned the engine off and key on Id be in the 11s, restarted and I was showing 12.5 at idle, 4000rpm would get me 12.7-12.8. Only way the battery light to come on was to turn the headlights on at idle, I wanna say voltage had to be down to like 11.9 to light it up.
Replaced the alternator, everything was fine. My guess is that one diode or feild went out but 2 were still trying

MetroMPG 10-31-2019 07:57 PM

Yeah, my batt voltage got as low as 7 and no light! Funny that your cruise control didn't like low voltage - just like my radio.

I'll check the cable connection to the alternator too.

2000mc 10-31-2019 08:19 PM

Check voltage drops while running. Alt output post to battery positive, and alt case to battery negative

nemo 11-01-2019 09:37 AM

Two problems? Is the light working and are they related?

MetroMPG 11-01-2019 09:57 AM

The light works. With the engine off and the key set to RUN, it's on as it should be.

oil pan 4 11-01-2019 12:31 PM

Intermittent alternator operations like that has been brushes in the past for me.

MetroMPG 11-01-2019 01:08 PM

Should I hit it with a hammer?! I'm going to hit it with a hammer!

redpoint5 11-01-2019 01:17 PM

I've fixed starters that way before.

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