Intermittent Alternator Light |
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Intermittent Alternator Light |
yeahmag |
Mar 21 2022, 11:22 AM
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#1
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Advanced Member Group: Members Posts: 2,422 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
Got a strange one... Alternator light started flickering on my way to this weekends autocross. This was on the highway at steady rpm of around 4K. I hadn't seen it flicker like this before: sometimes on dim, sometimes on for a few seconds at a time, sometimes flickering.
I figured I'd just carry on and hope I could make it through the event. As I pulled off the freeway on to surface streets the light went off and didn't come back on for the duration of the event. Packed up and headed home and only had a brief flicker or two while on the highway. I've never seen it come on while on surface streets or at idle. I figured I'd check the alternator for AC voltage (failed diode) and maybe change the belt (which I personally run on the loose side and is probably aging out). Anything else I should look for? Almost feels like a marginal VR, but I've never had one fail in this way. Thanks! -Aaron |
Spoke |
Mar 21 2022, 11:41 AM
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#2
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Jerry Group: Members Posts: 6,991 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
...the belt (which I personally run on the loose side and is probably aging out). There should be no slippage between the engine and the alternator. It should be tight enough that you can turn the engine using the bolt on the alternator pulley. Try tightening the belt a lot and see if it works better or not. |
emerygt350 |
Mar 21 2022, 12:18 PM
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#3
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Advanced Member Group: Members Posts: 2,147 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
...the belt (which I personally run on the loose side and is probably aging out). There should be no slippage between the engine and the alternator. It should be tight enough that you can turn the engine using the bolt on the alternator pulley. Try tightening the belt a lot and see if it works better or not. I have read that too tight a belt can do bad things to a type iv. Can't remember exactly what bad things, but bad things. |
yeahmag |
Mar 21 2022, 12:20 PM
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#4
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Advanced Member Group: Members Posts: 2,422 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
I'm leaning heavily towards the VR at this point. Seems to be a common failure mode.
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emerygt350 |
Mar 22 2022, 05:51 AM
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#5
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Advanced Member Group: Members Posts: 2,147 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
I recently installed a hella solid state, very impressed with it. 13.8 all day.
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yeahmag |
Mar 22 2022, 10:41 AM
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#6
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Advanced Member Group: Members Posts: 2,422 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
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914Mels |
Mar 22 2022, 10:50 AM
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#7
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Member Group: Members Posts: 357 Joined: 20-June 11 From: Santee Member No.: 13,221 Region Association: Southern California |
If it's an old alternator with lots of miles your brushes may just be worn to the point of losing the spring tension that holds them tight to the slip rings.
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yeahmag |
Mar 22 2022, 07:40 PM
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#8
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Advanced Member Group: Members Posts: 2,422 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
Totally unknown on the age and mileage. Always been rock solid. I would think (and I could be wrong here), poor brush spring tension would go away at higher RPM.
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914Mels |
Mar 22 2022, 08:19 PM
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#9
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Member Group: Members Posts: 357 Joined: 20-June 11 From: Santee Member No.: 13,221 Region Association: Southern California |
The shorter the brushes get the less the spring tension is pushing them down. Higher rpms will kick them up off the rings.
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Spoke |
Mar 23 2022, 11:57 AM
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#10
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Jerry Group: Members Posts: 6,991 Joined: 29-October 04 From: Allentown, PA Member No.: 3,031 Region Association: None |
You could run some simple tests with engine running about 2k RPM.
On the alternator connector on the relay board, measure: D+ to chassis ground (not the engine); should be the same as the battery DF to chassis ground; should be 5-10V D- to chassis ground; should be 0V Battery POS to chassis ground The voltages will let you know how well the battery, alternator, and wiring is doing. |
vitamin914 |
Mar 23 2022, 12:48 PM
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#11
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Member Group: Members Posts: 202 Joined: 8-September 21 From: Toronto Canada Member No.: 25,893 Region Association: Canada |
I recently installed a hella solid state, very impressed with it. 13.8 all day. Interesting. Mind sharing where you got it from? This is where I got mine a few weeks ago... https://www.pelicanparts.com/More_Info/0021...2-154-74-06-M44 |
emerygt350 |
Mar 23 2022, 01:07 PM
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#12
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Advanced Member Group: Members Posts: 2,147 Joined: 20-July 21 From: Upstate, NY Member No.: 25,740 Region Association: North East States |
I recently installed a hella solid state, very impressed with it. 13.8 all day. Interesting. Mind sharing where you got it from? This is where I got mine a few weeks ago... https://www.pelicanparts.com/More_Info/0021...2-154-74-06-M44 I think I got it from there as well. |
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