1993 GMC Sierra will not idel and will stall

1993 GMC SIERRA
120,000 MILES • 6 CYL • 2WD • AUTOMATIC
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CAPER33
  • MEMBER
  • 2 POSTS
Hi there,The truck will idel ok at first and then stall.Expeially if you turn the radio,wipers lights or heater on or put the break on.If I have the truck unstarted and turn the lights on,they are very very dim.I had the altenator checked and its perfect.If i was driving it,I will have to floor the truck so it wont stall and then come to a stop sign,it will stall again,Can you please tell me what the problem would be
Nov 11, 2009 at 5:36 AM
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JDL
  • ✓Experienced Mechanic
  • 16,098 POSTS
welcome to the forum. I'd have to make sure the battery has a full charge and the connections are good. Was the alternator tested on or off the vehicle? If the alternator was tested off the vehicle, it is possible the alternator may be ok, maybe problem with wiring circuit to or from the alternator?
Nov 11, 2009 at 5:49 AM
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CAPER33
  • MEMBER
  • 2 POSTS
Hi there,its a brand new batter with a full charge to it,yes the alternator was tested off the truck
Nov 11, 2009 at 5:58 AM
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JDL
  • ✓Experienced Mechanic
  • 16,098 POSTS


https://images.2carpros.com/forum/automotive_pictures/170934_gmc_alternator_1.jpg

The above is wiring circuit for alternator. If you turn on headlites with engine off, that is battery voltage. Use a digital multimeter across battery posts, everything turned off. 12.6 volts is considered a full charge. Start the vehicle, take second reading across battery posts, the second reading should be higher than the first, if it isn't, the alternator isn't charging for some reason. you can also take a reading at alternator bat terminal, same deal.
Nov 11, 2009 at 6:34 AM
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