FORD ALTERNATOR LOW OUTPUT

  • Tiny
  • Woodmanscott
  • FORD F-350

I have an 85 f-350 and the alternator does several things only two make me want to shoot it 1 st things is under a load the alternator get warm(i know this is normal) but it slowly loses power but when it cools off it is right back to full power. The 2nd thing is that at idle if you run the lights and heater fan you can see on the volt gauge it dropping drop it in gear and it dips below 11 volts.I have changed the alternator 3 time as well as the regulator I am running 1 ought cables from the battery and 3, 10 gauge wires from the alternator to the solinoid. It is a 100 amp ford alternator. I even installed a larger crankshaft pulley so at idle the alternator is now spinning 3 time that of the engine can anybody help me. Is there a better alternator that is made for putting out high current at low engines speeds or do they make a regulator that will excite the alternator at lower speeds and voltages

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Sunday, January 8th, 2006 AT 12:41 AM

8 Replies

  • Tiny
  • DARRYL
  • MEMBER

Hello: Try this. When the engine is cold touch the pulley on the alternator and see its temp. Start the engine and turn on a lit of stuff and let engine run for a few moments. Turn off engine and feel the temp of the alternator pulley. If it is quiet hot then the belt is slipping. Install a new belt of the proper width and tighten it good.
Perform that check (ps they don't always squeek when slipping)
Good luck
Darryl.

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Monday, January 16th, 2006 AT 10:04 PM
  • Tiny
  • Woodmanscott
  • MEMBER

Thanks I will check that and see if the pulley is infact getting hot and thanks again :D

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Tuesday, January 17th, 2006 AT 2:41 AM
  • Tiny
  • Dude
  • MEMBER

How is the ground connection between engine and frame :

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Wednesday, January 18th, 2006 AT 3:39 AM
  • Tiny
  • Dude
  • MEMBER

How good is the ground strap between engine & frame :

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Wednesday, January 18th, 2006 AT 3:41 AM
  • Tiny
  • Woodmanscott
  • MEMBER

I dont have one going from the frame to the battery. I have two going from the battery to the body of the truck :arrow:

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Wednesday, January 18th, 2006 AT 5:45 AM
  • Tiny
  • DARRYL
  • MEMBER

Hello: Typically you should have the Neg batt cable going to the engine block, and the Pos battery cable going to the starter, or to a starter solenoid, then to the starter. Then you should have ground straps going from the engine block to the sheet metal, usually at the firewall
good luck
Darryl.

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Wednesday, January 18th, 2006 AT 5:02 PM
  • Tiny
  • Woodmanscott
  • MEMBER

After reading what I wrote I saw that I was wrong I do have the negative cable (a 1 ought ) going to the engine block and and 3 #10 wires coming from the block going to the fire wall, core support and the left fender under the same screw as the factory harness ground. I have not pulled the alternator out yet to see if one of the diodes and come unsolderd or has burnt in half its just my opion but a 100 amp alternator should pull the heater, headlights and a stereo without falling below 13.8 the paper work that came with the alternator said its constant amp draw was 85 amps peak 100. Funny thing is I have a missubissi truck with a 50 amp alternator that pulls its heater and lights stereo and cb radio and barly gets warm

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Wednesday, January 18th, 2006 AT 5:27 PM
  • Tiny
  • DARRYL
  • MEMBER

Hello: Well possibly the alternator is defective, like you said possibly an open or shorted diode, or possibly bad regulator. If you have a GEN light sometimes they are part of the charging ckt, make sure the GEN light is indeed working and not burnt out. Possibly you could check the output with meter on AC scale to see if there is any ripple, check across the battery terminals. If you had a scope you could see the alt out put much better of course
good luck
Darryl.

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Wednesday, January 18th, 2006 AT 8:01 PM

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