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matrophy

No charge at cold start - alternator works after 1500 rpm

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From a cold start, "BAT' light is lit and voltmeter shows slightly above 12V. If I rev to 1500 RPM, 'BAT' light shuts off and voltmeter shows roughly 14V. Subsequent driving and re-starts later in the day show normal charging and voltage. I stopped by AutoZone and they checked the alternator and they said it was OK. I found a loose connection from the battery to the fusible link and cleaned all terminals and retightened everything down and checked the belt but the issue remains. I did have the alternator disconnected to pull the engine and the connections seem OK now. It seems odd that it continues working OK for the rest of the day after I rev to 1500 RPM when I start her.

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I had a similar problem with my 77 buick. It turned out that a previous mechanic had installed a new alternator that had a smaller pulley on it.  When I replaced it with a larger pulley the problem was eliminated.  Now the car will charge at idle.

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28 minutes ago, matrophy said:

From a cold start, "BAT' light is lit and voltmeter shows slightly above 12V. If I rev to 1500 RPM, 'BAT' light shuts off and voltmeter shows roughly 14V. Subsequent driving and re-starts later in the day show normal charging and voltage. I stopped by AutoZone and they checked the alternator and they said it was OK. I found a loose connection from the battery to the fusible link and cleaned all terminals and retightened everything down and checked the belt but the issue remains. I did have the alternator disconnected to pull the engine and the connections seem OK now. It seems odd that it continues working OK for the rest of the day after I rev to 1500 RPM when I start her.

 

22 minutes ago, jagman said:

I had a similar problem with my 77 buick. It turned out that a previous mechanic had installed a new alternator that had a smaller pulley on it.  When I replaced it with a larger pulley the problem was eliminated.  Now the car will charge at idle.

The weird thing is that once it hits 1500 RPM it charges fine for the rest of the day.

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19 minutes ago, thisismatt said:

External regulator?

No. Internal

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Sounds like the alt is faulty then. Autozone's alternator tester is next to worthless in my experience.

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I have two running 521 trucks that I am currently running internal regulator alternators in.  Both of them need the engine RPM bumped up to around 1500 RPM to charge, then work normally.

I just live with this, it allows me to start the engine, and not have the alternator load the engine, until the engine warms up a little bit.

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Nissan switched to internal regulated for all '78s and up.

 

 

Has this just happened? If so this will mean the wiring hasn't been altered.

 

Inspect the two wire plastic plug in the back.  Make sure they both make good snug contact. 

 

 My trouble shooting of the charge system says light not going out or dim/flickering at normal idle is (like Matt said).... bad alternator

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16 minutes ago, datzenmike said:

Nissan switched to internal regulated for all '78s and up.

 

 

Has this just happened? If so this will mean the wiring hasn't been altered.

 

Inspect the two wire plastic plug in the back.  Make sure they both make good snug contact. 

 

 My trouble shooting of the charge system says light not going out or dim/flickering at normal idle is (like Matt said).... bad alternator

Just happened after reconnecting engine making me think it's the connector but it seems fine. There is some mention of 1500 RPM in the charging system troubleshooting tree but I'm not clear if that is relevant to my situation.

2020-07-29_19-31-56.jpg

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If it charges I tend to just keep my eye on it for other changes.

 

Nissan made a really strange alternator system on the 720 diesel engines, when I turn the key on to let the glow plugs warm up the charge light comes on, after starting the engine the light goes out/off, but I have a volt meter and it does not show a charge, now the light is off, about a minute later I hear a click and the volt meter shows a charge and the idle rises after that.

Now the really strange part is I wear out alternator belts fast, I believe what is happening is when it is not showing a charge my 720 belt squeals something awful, but after it clicks and starts showing a charge it never squeals again unless it is wore out, for some reason when it is not showing a charge for that minute the alternator is harder to turn and wears the belts out, but the dash light goes out when the engine starts.

 

It may be a 1986 thing, the 1986 alternator has a oval plug with 3 or 4 wires while early 720s have the "T" plug, just keep an eye on the volt meter.

 

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That tree, by your symptoms, points to faulty ACG, alternator parts except IC regulator.

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I’m not a alt expert.but I would let it get up to charge .14 volts then get to 1500 rpm and put the lights and wipers or heater on.If it stays above say 13.5 bolts-13 bolts I say the alternator is good.if in the 12.5v range it’s getting stressed.

maybe there is a GM made alt in there.those are the self exciting type that have to reach a certain speed before they kick on

would help to say what car truck this is.

what is a ACG?

 

external volt reg?mechanical?

Edited by banzai510(hainz)

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