Help needed. Big time.

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by txguy, Oct 6, 2001.

  1. txguy

    txguy 1/2 ton status

    Sep 4, 2001
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    Round Rock (Austin) Tx
    Good morning/afternoon all. First off, I am electrically inclined enough to wire a car stereo. After that, well... Anyway. I have a brand new battery, new 94 amp alt, and new blower motor. I have severe voltage fluctuations (sp) between 8.5-13 volts. Couple of questions. When you go from park, to drive/reverse/neutral does anything happen to the electical system other than a slight RPM drop. Is there something in the tranny, or else where that engages electrically that would draw 10-20 amp maybe when you put it in gear? (guessing there is based on the voltage drop of about 2-4 volts) And after that when engaging 4 wheel hi/lo from 2wheel high is there something electrical that would engage again on top just being in drive/reverse/neutral? I get another drop when I go into 4wheel drive mode. Other than that, I get fluctuations by several volts based on sitting still at a light, or driving. Sometimes its low at idle (9 volts), other times its about 13 volts. On a different day, same electrical items running (headlights, no offroad lights, interior fan on vent, not a/c mode, and in gear) I will get a great reading at 13 volts at idle, and then as I go it drops to 8.5 volts-10 volts at speed. This is random and fluctuates sometimes in an opposite manner from the day before based on the position of the moon, time of day, and what mood the truck is in etc. I have noticed in the last 3 days, when I am driving at night the lights flicker various degrees of dimmer/not dim when I go over a small bump in the road going down the highway, then after bump it the flicker is gone, even though there is still a voltage problem. All along I have wondering if its wiring loose or something like that. Now I kinda think with the bumps and the flickering that is surely is. However, I just got an electircal system check, he said my brand new alt is bad. I told him it was new, and the old alt did the same behavior. In fact when I took it off, it tested good. Now, the new one may have a problem (burned up maybe). At this point he told me to replace the alt. Why? I really don't think thats it. He said that there is too much load on it. The OEM is around 70 amps I believe, this one is a 94 amp model. He says that I need another one rated for yet more amps. Yet, the problem is the same, etc... I informed him of this. Either he is wrong, or does not want to deal with digging into the problem more to find the issue. He said it would be about a 150 bucks to pull the stuff by the volt meter on the dashboard to start tracing and checking the wiring back to the starter/battery. I don't want to get into something that become a lost cause, and spend bucks and get no where. At the same time, I have thought it may be easier just to rewire a few things... (battery to starter area, alt to starter area, the wiring from the engine area to the inside fuse block) and see if that helps). How hard is it to rewire those areas? Also, has anyone had these issues before? That guy said several times, he swears the alt is the problem, that and when good it does not kick out enought juice. I don't think thats it, because its 25 or so above OEM rated alt... Anyway, please!!! Also, I am leary of getting a larger alt, because if there is a real problem, I don't want burn up that alt, and more important, force feed more juice into a troubled system, and have it get hotter, and then have a fire start.
  2. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

    Jul 23, 2000
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    E-town baby!
    When I drove to Texas in May my Jimmy had a fluctuating voltage problem. I would notice my lights were geting brighter, looked down at the voltage guage and it was at 18 volts [​IMG], then within a couple of minutes it would drop down to normal ~13.5 volts and the lights would go back to normal. Eventually the alt went completely. When I swapped in another alt my voltage was ~12.5-13.5 at idle and about 14 volts at anything over idle. The only time it goes below 12.5 is when its idling really 450 rpm and I have my lights on and heater going.
    I would remove your alternator and take it in to be tested independant of your electrical system. If it checks out OK then you know to look elsewhere for the problem. I suspect your alternator is toast though. I have had several alternators that were bad right out of the box...especially the rebuilt ones.


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