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Charging system problems...

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by txbartman, Jul 11, 2002.

  1. txbartman

    txbartman 1/2 ton status

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    Okay, I was having problems with my alternator. With the engine off, i had about 12.5V or so across the battery terminals. I also checked and confirmed the same across the pos batt and the engine block as well as the frame and body.

    With the engine running, there was very little difference (maybe up to 13.0). With the a/c on and the engine at around 2500 RPM or greater, I was getting about 11.8V or so. In addition, my voltmeter, which has always seemed a little low, was staying in the red around 8 or 9. After cruising at highway speeds for a while with no a/c or nothin, it would get up to around 10, but never straight up (13).

    So, I replaced the alternator. Installed a one wire PM 140A unit. This unit was dyno'ed at 93A idle/140A highway speed. Got it all hooked up last night. I run a 2GA charging wire direct to the pos post and have a wire at the bottom bracket going to the neg post. But, after firing it up, I have essentially no change in the readings.

    What's up? Could I have a bad ground on the alt? My neg wire is a 2GA wire. If you are looking at the front of the engine, it is stacked this way... bolt head, wire, bracket, alt, rear bracket, 3 washers (spacing reasons aligning pulley), block. Something I remembered last night is we repainted all my brackets when we dropped in the new engine in Jan. Could I have hurt my ground connection that way? How can I test it? If i run a wire straight from the casing to the neg post, should I see a jump in voltage if that ground is the problem?

    Where do I start on this one???? /forums/images/icons/confused.gif
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    You could try running auxiallary grounds just for testing, nothing permanent and see what happens I guess. I've never had a problem like this, but I'm pretty anal when it comes to connections. All (pos and ground) are scraped/wire brushed clean, then die-electric grease is used before stuff is put together. For the grounds I use that battery terminal goo thats supposed to prevent corrosion. (works pretty good too)

    On my truck, the neg batt wire is bolted straight to the top of the upper alt bracket, since A)wasn't sure where it was supposed to go, and B) it is a very convenient location : ) It's that and the rear braided strap to the body for my truck's engine grounds.

    I'm kind of surprised though, if a ground was the problem, you'd *think* the alt would STILL be trying to "push" out more voltage at higher RPM's and under a heavier load, (so you'd see tha when measuring at the alt) thats just the way they work. But HOW they "sense" the increased load, I'm not certain. I know the voltage regulator is tied into this, if its shot, the voltage doesn't change based on RPM OR load.

    Is the new Alt a one wire, two, or three? (I *think* most stock ones are considered two, mine has a two prong plug, and then the single red wire to one terminal...not sure if they count it though)

    The only things I can think of after all my speculation and rambling, is that either the new alternator is bad (happens) or that the alternator just isn't "seeing" the increased load somehow. But as I said, I'm not sure how that works.

    I hope someone chimes in that *really* knows this electrical stuff, but I'm thinking the load the battery sees is what the alternator bases its output on? What kind of voltage drop are you getting from the pos. batt terminal to the starter, and at the pos. junction block on the firewall? (if your vehicle has one, if not, just check voltage at anything on the fuse panel that is "hot" in run, both might be ideal, you may have poor fuse panel/engine harness connections too)

    I would guess that corrosion on the terminals/connections at the starter solenoid *could* prevent voltage from reaching the fuse panel/everything in the truck, and a check of voltage at the batt terminal and the junction block/fuse panel would tell you if a connection there is poor...I mean a simple continuity test will tell you if your grounds are "good", and if you have continuity, and the ground wires aren't hot, I wouldn't focus solely on a grounding problem. If you've got a major difference in voltage before and after the starter (pos. batt wire goes to same terminal that feeds the fuse panel) then I'd imagine a conneciton on the solenoid is at fault. My fuse panel (all stock original wiring except new replacement pos. batt cable) sees only a couple of tenths of voltage loss from either the alternator or battery, and the gauge is almost dead on.
     
  3. txbartman

    txbartman 1/2 ton status

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    i had a guy in my 4x4 club tell me it takes a minute or so for the regulator to "warm up" and for the alt to go to work. With the new alt, all I did was fire it up and test it at idle. I am confident this alt is good. I have heard of new alts being bad, but never a dyno'ed powermaster unit.

    I am going to try driving it some tonight and see if the regulator just hadn't put it to work yet. I will also check my starter connections as I am replacing my stock starter with a Powermaster XS Volt starter tonight anyway.

    The stock alt, BTW, has three wires. One is a a charging wire and usually runs to the pos battery terminal. That one is by itself. The other two wires are in a plug. Of these wires, the red one goes to the starter post and is used to provide current to the regulator from the battery. The second wire in the plug is actually only used if you have idiot lights. If you have idiot lights, it controls the "charging" light. If you have guages, it does nothing (at least, that is the best i can figure from the schematics). A one-wire alt has a built-in jumper to the regulator hence eliminating the need for the additional wire.

    As far as grounds go, my neg post grounds to the alt, to the frame, and to the body. The block grounds to the body at the back. I think those are all the grounds I have. i am going to work on the alt ground tonight and see what happens.
     
  4. SkulzNBonz

    SkulzNBonz 1/2 ton status

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    I ran into a very similar problem a couple of weeks ago. I replaced the alternator, and everything seemed fine. After a few miles of running my alt. was showing discharge. I thought perhaps I had gotten a bad alternator as well. After some careful wire tracing, I found two spots where the insulation had been worn/burnt off the wiring and was shorting out. After a quick tape job, it has pulled 13+ ever since. I been burnt one too many times tracing a problem to find out it was a simple fix. I would look for a short before I go after the big stuff. My .02.

    John
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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  6. dyeager535

    dyeager535 1 ton status Premium Member

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    Yes, those two prong plugs into the alternator case are typically pretty fouled, brittle, and the wires usually aren't in good shape either. An easy thing to look for as well. I'd imagine you would notice this when changing an alt, but you never know, it may *look* ok.
     
  7. SkulzNBonz

    SkulzNBonz 1/2 ton status

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    Yep. With the wiring being caked with dirt,mud, and grease, those shorts were well camoflouged.

    John
     
  8. Anteak

    Anteak 1/2 ton status

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    Sorry, I don't know much about the electrical systems, but have you checked the battery? Put the battery under a load test to see if it will "recover". Will a bad cell cause a low charge? If your instrument gauges read lower than the gauge you put across your battery posts then at 10 volts while driving could be 13.5v at the battery. Still not enough for a good charge, but try to eliminate your variables before replacing your alternator again.
     
  9. kpanza

    kpanza 1/2 ton status

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    Like Dorian said, on the one-wire alts, you need to "excite" them by reaching a certain rpm...you need to plug the stock harness in if you want it to automatically excite when the motor starts. I think the RPM excite is set for like 1500 rpm or so...
     
  10. txbartman

    txbartman 1/2 ton status

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    I talked to Powermaster just a while ago (their tech support is GREAT). They said that I need to bump the throttle once and it will start charging. He also recommended that I move my ground cable from the bracket to the case via one of the "extra" bolt holes on the back of the case. He said grounding the case is the ultimate ground you can give an alt.

    I plan to try all this fun stuff tonight when I get home. Come on 4 o'clock!
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    It's not going to be any better of a ground than the way you have it if the surfaces are semi clean. People get way too carried away with wiring stuff when the difference just isn't worth it, if one exists at all.

    Since you are having problems though, cleaning up contacts if not already done, can not hurt, and may prevent problems in the future, so isn't time wasted.
     

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