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Legit tech question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Leadfoot, Mar 28, 2002.

  1. Leadfoot

    Leadfoot 1/2 ton status Premium Member

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    I have a NAPA alternator on my 80. It's the 63 amp output style stock wiring configuration. Sometimes at idle it does not charge (charging system reads about 12.3V). When I give her a good blip on the throttle it starts to charge (around 14V). I was looking at the wiring and there is one red wire that goes to the post on the back of the alternator and splits and goes to the two wire plug on the alternator and the other end goes to the fuse block which then goes directly to the battery. The other wire in the two wire plug is a white wire and is known as the exciter wire. Is this the wire that is messing me up and where does it go to? This is the second alternator which I have gotten (of the 63 amp style) and they both have done this. Is this normal? I'm just worried that I am going to leave it idling sometime with the truck running and lights on and it's going to drain. Any thoughts?
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Normal with these kind of alternators. Kick the idle up and keep it there, the alternator continues to charge. Drop idle below a certain RPM, and output drops off noticeably. Apparently, its jsut due to design, and the only way to fix it is replace the thing with a better design.

    As long as you are at 12v or greater under load (lights, heater on high, etc., at idle) and it goes over 12V cruising, you won't have problems. But I don't like seeing that either. Very "large" swing in the needle at a low idle speed compared to anything above, say 800RPM.
     
  3. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Normal. If you could find a smaller pully for the alternator it would increase the speed the alternator spins at. Might be easier to put a bigger pully on the cank. Either way will work. Truck should idle at about 650rpm in gear. if your idiling down around 500 it might be just kicking up the idle will cure it.
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    Anyone located any smaller stock alternator pulleys? I've kind of been looking, but 2.5" seems about the norm.

    I'm not aware of different size stock crank pulleys, anyone?
     
  5. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    I know they are out there. The pullys on my 75 are differnt that the pullys on the engine in the 79 (it has 85 pully's). all are factoyr from various years. Let me check the pullys off my old 79 engine and see what diameter the pully is that drives the alternator. Might be a day or so. That engine is barried in the corner of the garage.
     
  6. dyeager535

    dyeager535 1 ton status Premium Member

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    That would be cool. Most of us don't turn our engines at so may RPM's that slightly increased alternator RPM's is gonna make a difference. I really only need about 200more RPM's at the alternator at idle to be rock solid, so a slightly smaller pulley would be great, or a slightly larger crank pulley. But with crank pulleys, you start running into AC, no AC, smog pump, no smog pump, two different diamters on the same pulley, etc. (or so I think...Olds is that way)
     
  7. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Yeah you do run into some problems. On my 75 and I'm pretty sure the 79 is the same the back 2 pullys are the same diameter. The alternator runs off the third and then if you got smog there was a 4th (the 85 set up has 4). On the 85 accessories the pully agains the block is about 2 inches smaller then the second then that alternator....Hmmm maybe it;s the 75 and 79 that are that way...anyway Hmmmmmmm Now I'm geting a head ache LOL.....Both trucks and the engine are at home....I'll have to look LOL. Might not be as simple as I thought cause the water pump shares that alternator pully and the second belt also runs off the water pump then the PS pump. So it would require changing crank and power steering sets to make it work.
     

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