1980 280zx voltage fluxuation - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #1 of 14 (permalink) Old 05-18-2019, 10:12 AM Thread Starter
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1980 280zx voltage fluxuation

I just purchased a 1980 280zx. I'm waiting for my shop manual but wanted to see if anyone can help with this issue:


The car runs amazing but upon starting the voltmeter goes from about 14v and slowly runs up to about 17v then drops back to 14v and fluxes from 12-16v (estimated). This caused all the lights to very slightly pulse like a strobe light.(its minor but you can see the pulse) I have checked the battery voltage at rest (12.6v) and it seems fine. The alternator is new and recently installed. (this could be the issue) It is charging at 14.2-14.7 and is good even under load with lights on. I've checked all the grounds and did the test between the positive and negative battery leads to the case and brackets on the alternator and they were less than .02 volts. Does this car have an external voltage regulator? Perhaps this new alternator has a bad internal regulator? I'm running out of ideas.....any help? So stoked to have this car because I had the same one in high school back in 1982. Thanks, White Salmon, WA
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post #2 of 14 (permalink) Old 05-18-2019, 11:09 AM
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I would think anything more than 16v is a problem. really should be around high 14's to low 15's typical. did you test it with a good voltmeter at the batt terminals or are you relying on the gauge in the car? when you said its charging at 14.2 -14.7 that sounds like you used a voltmeter at the battery, if so, its just the gauge that is flakey. If you wanted to check that you would need to test the gauge with a variable power supply, see how well it tracks to a good multimeter. If that test ok and the alt output is as you say, then it pretty much has to be a wiring issue, perhaps something in the connectors. Process of elimination if you want to resolve it.


oh and NO the external regulator if its stock.

Last edited by Dave M; 05-18-2019 at 11:14 AM.
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post #3 of 14 (permalink) Old 05-19-2019, 02:44 AM
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You've got a bad voltage regulator circuit. Voltage that high will cook the battery and could damage circuit electronics.

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post #4 of 14 (permalink) Old 05-19-2019, 10:28 AM Thread Starter
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You've got a bad voltage regulator circuit. Voltage that high will cook the battery and could damage circuit electronics.
I agree that the voltage regulator is not working correctly. It is keeping the voltage close to the correct level but then it "pulses" or "fluxgates" rabidly and the lights very slightly flicker. Here is my question.... Is the voltage regulator built into the alternator or is there a voltage regulator somewhere on the car? If it's external where is it? If it's internal, I need to replace the alternator I assume? Thanks
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post #5 of 14 (permalink) Old 05-19-2019, 10:31 AM Thread Starter
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I would think anything more than 16v is a problem. really should be around high 14's to low 15's typical. did you test it with a good voltmeter at the batt terminals or are you relying on the gauge in the car? when you said its charging at 14.2 -14.7 that sounds like you used a voltmeter at the battery, if so, its just the gauge that is flakey. If you wanted to check that you would need to test the gauge with a variable power supply, see how well it tracks to a good multimeter. If that test ok and the alt output is as you say, then it pretty much has to be a wiring issue, perhaps something in the connectors. Process of elimination if you want to resolve it.


oh and NO the external regulator if its stock.

can you clarify please. Are you saying that there is not an external regulator? That would mean the regulator is inside the alternator that was just replaced?
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post #6 of 14 (permalink) Old 05-19-2019, 11:43 AM
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can you clarify please. Are you saying that there is not an external regulator? That would mean the regulator is inside the alternator that was just replaced?
Dave is correct, starting with the 1978 s30 and moving into the 280zx, the external voltage regulator was eliminated - his alternator is internally regulated.

The fact that it's internally regulated doesn't mean that the internal voltage regulator can't be bad. These alternators are all rebuilt in China - I went through 3 of these before I got one that worked as it should (first one had the hemispheres misaligned so it wouldn't fit the bracket and the second one's bearing went out within a week).

Before you take it back for another one, sand the fusible link terminals/links - on an s30 if the charging link is bad it can create all kinds of problems. If that doesn't fix it go exchange it for another.

1978 280z - stock L28 engine - Dallas, TX
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post #7 of 14 (permalink) Old 05-19-2019, 05:07 PM
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If you have a local automotive electrical shop, take your alternator to them and have them replace that voltage regulator circuit.
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post #8 of 14 (permalink) Old 05-20-2019, 11:13 AM Thread Starter
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Dave is correct, starting with the 1978 s30 and moving into the 280zx, the external voltage regulator was eliminated - his alternator is internally regulated.

The fact that it's internally regulated doesn't mean that the internal voltage regulator can't be bad. These alternators are all rebuilt in China - I went through 3 of these before I got one that worked as it should (first one had the hemispheres misaligned so it wouldn't fit the bracket and the second one's bearing went out within a week).

Before you take it back for another one, sand the fusible link terminals/links - on an s30 if the charging link is bad it can create all kinds of problems. If that doesn't fix it go exchange it for another.


Thank you. That's what I was thinking too. I plan on replacing the "new" alternator and going seeing if that solves the problem. I'll also confirm links are clean and throw in a new fuse just for fun. Is s30 referring to the size of the fuse on this circuit? Thank you again,
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post #9 of 14 (permalink) Old 05-21-2019, 09:13 PM
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If you are handy with a soldering iron you can replace the voltage regulator. There are five pins to de-solder and re-solder.
VR on ebay $ 9.22
https://www.ebay.com/itm/Standard-VR...frcectupt=true


It took me about an hour to repair. I took it to Autozone afterward and had them check it. All checked out.
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post #10 of 14 (permalink) Old 05-22-2019, 12:53 PM
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Thank you. That's what I was thinking too. I plan on replacing the "new" alternator and going seeing if that solves the problem. I'll also confirm links are clean and throw in a new fuse just for fun. Is s30 referring to the size of the fuse on this circuit? Thank you again,
s30 is what 1st gen Zs are referred to as (so we dont have to write 240z, 260z, 280z each time).

1978 280z - stock L28 engine - Dallas, TX
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