Question about 1987 Toyota Land Cruiser

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Not charging at low idle

When the engine is at low idle, the alternator is not keeping up

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Some times when the alternator brushes is short can be,.so check alternatoe brushes.

Posted on Nov 07, 2008

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How have you determined "not keeping up"?

We need to diagnose whether the culprit is the alternator or battery (or something else like an accessory drawing more than normal current)

With a digital voltmeter (not analog) , measure battery with car off, then compare battery at idle.
Off reading = about 12.6 - 12.8 volts DC
Idle reading must be higher than above or no charging will take place, Idle volts typically 13 - 13.5 and should increase a bit with RPM until regulator limits the increase.

Some possibilities are :

  1. bad diode in alternator (can be replaced separately in many alternators)
  2. bad regulator (built-in to modern alternators)
  3. bad connection at battery terminals (wire brush or use battery terminal cleaning tool)
  4. bad battery (shorted cell, often caused by allowing water level to go below tops of lead plates)

Posted on Oct 25, 2008

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Idle drops way low with fan,lights,ect..., on@ operating temp195, IAC is good power,no leak, power from computor;yes,under load, lights ect..,what am I overlooking? 91GeoMetro 3 banger

The electrical load on the alternator will pull the engine RPM down. It takes 10 H.P. to run the alternator. The only recourse to low RPM at idle would be to install a larger diameter pulley on the alternator. Extended idle could result in low battery charge rate. Should be fine at hi way speed. The alternator will not put out below 750 Rpm.

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Why my alternator dont charge at normal engine idle thanks

You have rvc/regulated voltage control, that circuitry is in your pcm. I'm not saying the pcm is faulty, at the moment, I don't know? You also have a battery temp sensor in the battery tray housing, that might cause problems?
Check for applicable charging system trouble codes, if you haven't already.

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Check the alternator and the charging system. You may have a weak or failing alternator. If you have a voltmeter, get the battery reading with the engine off. A charged, good battery should show at least 12.6 volts. If you have to boost it, it must be low on charge. Recharge it or have it tested, a dead cell in the battery would not let it charge up.
Now take a reading on the battery with the engine idling, or idling as low as possible without dying. A good alternator and charging system will make the battery now read at least 13.5 volts. If your reading is lower than this, you probably have a weak alternator.

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Voltage light is illumiated and goes off during accelleration

The engine revs at idle are too low under 600 ( 750- 900) and the alternator is not charging. You will be reading around 11.5 volts up to 14.5 volts . You will need 12 v minimum to keep the light off.

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My battery light keeps coming on in sporadic manner. It will start fine at times.

If your engine idles too low, below 600 RPM, then this will often cause a drop in charge to the battery. The alternator needs to spin at a given rate to provide enough amps for charging.

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Why does the voltage drops when idleing,

Your idle speed may be too low. It is common for the Alternator to slow down with the engine RPM. You can get a free scan of your charging system at Autozone or Oreillys. You may have a lazy Regulator which is not allowing more power through.

Some cars like Ford products have a sensor which automatically increase idle speed to keep the Voltage up. In your brand you need to ask a Dealer. When your car has more equipment demanding power than the Alternator produces, the Voltage will drop.

You may want to install a new Serpetine belt and check your Tension pulley for a tight fit. If the belt is sloppy it can effect the charging system.

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Upon startup engine idles rough then speeds up and returns to normal idle .After a couple of minutes the volt light comes on then no power then a complete shut down.Starts back up for a while then shuts...

OK, the volt light means that the alternator is not charging the battery. It could mean the battery is shorted out, or the battery is bad or low on charge due to an alternator not charging.

Replace the Alternator and battery as indicated by standard voltage output tests under load.

The computer in the car will not operate the engine properly on low voltage.

Fixing the charging system, may resolve the rough idle (meaning that it may be trying to relearn after data was erased by low voltage of the battery), and the speed up.

Try the charging system first, and once that is repaired, reevaluate the engine driveability and speed and idle smoothness, after it relearns.

Good luck on this repair.

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These trucks have what is called a smart charge system. It normal for the alternator light to elluminate when the truck requires no charging or the idle is low. The most likely reason you have low idle is throtttle body coking which requires cleaning or a bad idle air control valve. Also clogged injectors will cause a low rough idle but if that was the case misfires would show up and can be seen while they happen using a diagnostic data scanner.
And the first thing we always look at is the air cleaner. If you have a K/N filter the oil can contaminate the MAF senor. If the sensor cannot see and feel the air then it won't be able to add fuel causing a low idle, The MAF can be sprayed with brake cleaner to clean it. Usually you will get a p0171 and or a p0174 if the maf was causing a lean condition.

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Now change the sulfated batery for a new one.

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charge it up .crank engine while its idling get a volt meter hook it to battery .volts should be 13.5 to 14.5 if its 12 to 10 or lower.alternator is not charging.if alternator is charging . turn engine off battery should stay 12.5 volts if it drops after engine is off to 11.0 or 10 volts battery weak replace it.

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