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Discussion Starter #1 (Edited)
Hey everyone, before I start this thread I wanted to say I did search for this issue and found a ton of useful info that I will be using, but I didn't find anything too similar to my specific issue. That being said, let's get into it!

The car is a 1993 Geo Tracker, 4x4, 1.6L 8v. My alternator died out on me last week, (was totally toast, would not free spin) and so I threw an autozone reman in and it was putting out 12.8v. Took it back, of course they said it was fine, but I got my money back so whatever. Threw a brand new alt from rockauto in and now I'm getting anywhere from 12.25 to 14+. I played around with my multimeter and recorded all the results I could think to look for.

Battery light is ON with key on, engine off. And OFF with engine running.

I grounded out the battery directly to the chassis with jumper cables and that had no change in volts.

Also, with the radio set to AM, I get a popping noise when pressing the brakes or turning on any electronics. Does the same for FM but the volume has to be much higher to hear it.

Things I'm going to try and get done this weekend are:
New pos. and neg. cables, check RH fender fuse box for corrosion, and maybe do some continuity testing if I have time.

Here are the results from testing around.
94943

The IG and L refer to the plug to the alternator

If anyone has any suggestions on what else should be done or what to look for, please let me know!

Thanks
-Ryan
 

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battery is either flat....or not holding charge or has a dead cell, 11.8 ign on is flat. should hold over 12 ign on with nothing else running. charging ok at 13.6, looks like the lead between alt and battery has a bad connection, wouldn't expect to see that much volt drop. Replace the lead or re do terminations.
What revs with lights etc on? should be done at 2500 to 3000 rpms, i'd expect volts to be up at 13.8 to 14.4 during that test. low at that point indicates a flat battery and alternator can't keep up, or a high resistance in alt output lead to battery.

Fully charge battery on a charger and repeat tests, or swap in a fully charged battery and test again.
Alternators will not fully charge a battery if its been let get too flat as they have a large rise in terminal voltage which shuts the regulator down to a tiny trickle of current.
Also might be an idea to get a charge load test done that will check alt is outputting required current.

I grounded out the battery directly to the chassis with jumper cables and that had no change in volts.

Also, with the radio set to AM, I get a popping noise when pressing the brakes or turning on any electronics. Does the same for FM but the volume has to be much higher to hear it
you have confirmed a bad connection in the alt to battery lead, you have (I assume) jumped the ground side but haven't done the other half of the circuit, the battery to Alt lead. pops on the radio is arcing across a high resistance joint, connection at alt should be spotless, no signs of green or black corrosion on the wire where it goes into the lug, same at battery terminal / ALT fuse.
 

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Discussion Starter #3 (Edited)
What revs with lights etc on? should be done at 2500 to 3000 rpms, i'd expect volts to be up at 13.8 to 14.4 during that test. low at that point indicates a flat battery and alternator can't keep up, or a high resistance in alt output lead to battery.
The test with the lights and accessories on was after driving it, idle revs were at around 1,000 rpm. I connected the voltmeter and revved the motor to about 3,000 with little to no change (little meaning it dropped slightly, then raised back up after letting off).

battery is either flat....or not holding charge or has a dead cell, 11.8 ign on is flat. should hold over 12 ign on with nothing else running.
The battery post to post reading was 12.23, but when I tested the alt plug directly, I got the 11.80 and 11.91 readings.

And I will do the alt to batt jump test this weekend and swap in a fresh fully charged battery to look for any changes.

One thing I forgot to add last night is that when I initially start the car, the volts at the terminals and lug start from 12.XX and creep to the idle volts I posted in the photo. Shouldn't they jump straight to the final charge number?

EDIT: I just went out and tested some more. After letting the car warm up and climb to the peak achievable volts, it tested 14.00+ at the lug, 13.90+ at the terminal TOUCHING THE EXPOSED POS WIRE, and 13.80+ DIRECTLY ON BATTERY POST. I'm no electrician by a long shot, but this is making me think bad battery? The only part throwing me off is that I let the car sit for 24 hours and it still started right up, no problems.
 

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One thing I forgot to add last night is that when I initially start the car, the volts at the terminals and lug start from 12.XX and creep to the idle volts I posted in the photo. Shouldn't they jump straight to the final charge number? [/QUOTE} nope, not until the alternator is spinning fast enough for the regulator to kick in.


[QUOTE} EDIT: I just went out and tested some more. After letting the car warm up and climb to the peak achievable volts, it tested 14.00+ at the lug, 13.90+ at the terminal TOUCHING THE EXPOSED POS WIRE, and 13.80+ DIRECTLY ON BATTERY POST. I'm no electrician by a long shot, but this is making me think bad battery? The only part throwing me off is that I let the car sit for 24 hours and it still started right up, no problems.
which lug? the one on the alt? if you are losing 0.1V at any point between wire and lug then that connection is bad. Ohms law states that you have resistance, volts will drop when current increases, and heat will be developed, leading to more resistance. As resistance in this situation doesn't change initially, but current goes up a lot as load goes onto the alternator, volts will fall as current tries to increase leading to lower volts with more load which you see when lights are on.
If connections are all good you should read same voltage on alt terminal going to battery and at battery post.
Any difference in readings its in the lead (and inline fuse) to the alternator. Replace that lead, and try a fully charged battery. I suspect bending the wire when changing the alternator has been enough to cause a high resistance joint to develop.
 

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Discussion Starter #5
Here's a real quick update on this issue. I replaced every bit of charging system wiring in the engine bay (exciter, fuse box to batt, batt to starter, ground) and battery terminals and put a brand new interstate battery in. Charging is at 14.3X while warming up and drops to around 14.2X once at warm idle. I have a solid .5X volt drop from the battery terminals to my cigarette lighter. I also still have a slight volt drop from the alternator to the battery.

Now the problem is, as soon as I turn on any accessories, the voltage drops to around 12.2X volts at idle, and around 13.00 while revving the motor. Headlights and heater on full blast and it won't go above 12.XX volts.

My next move is to replace the ground for the fuse box and do some continuity testing from the starter to the fuse box. And do add a battery to chassis ground again (I did not put that wire back when I redid the ground).

Any other tips I should keep in mind while doing all this?
 

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Check resistance from the alternator body to battery negative terminal. People forget the fact the alternator case is the return path and if the battery negative terminal to engine lead is corroded or making bad connection, or the alternator mount is dirty where it attaches to the engine, then output volts will reduce as load increases, exactly as you are seeing. Measure the resistance and work towards one end or the other to find the bad connection.
 

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Discussion Starter #7
Check resistance from the alternator body to battery negative terminal. People forget the fact the alternator case is the return path and if the battery negative terminal to engine lead is corroded or making bad connection, or the alternator mount is dirty where it attaches to the engine, then output volts will reduce as load increases, exactly as you are seeing. Measure the resistance and work towards one end or the other to find the bad connection.
While the alternator was out, I removed the mount and completely revamped it. I primed and painted it to avoid future corrosion, but made sure to take all contact points back down to metal. I cleaned every contact I could think of and the battery ground is a brand new 6 gauge wire, bolted straight to the starter mount. That being said, I will check the resistance just to be sure!
 

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only 6 gauge? sounds a bit light. I'd be using 4 gauge battery to the engine and at least 6 battery to the body ground by the battery. All the contact points clean? like the alternator pivots where they bolt to the mount? mount to engine?
Check resistance with a multimeter and see what it is.
 

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Discussion Starter #9 (Edited)
only 6 gauge? sounds a bit light. I'd be using 4 gauge battery to the engine and at least 6 battery to the body ground by the battery.
I might try swapping those out for bigger wires then. I only used that size because that's what I pulled out. 6 gauge for battery to starter and ground, 8 gauge for everything else. And yes, all contact points have been completely cleaned.

Edit: I forgot to add that I still have popping over the speakers when using any accessories or pressing the brakes. Only on AM radio though.
 

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Edit: I forgot to add that I still have popping over the speakers when using any accessories or pressing the brakes. Only on AM radio though.
you have a loose connection somewhere creating RF interference. You are still chasing a bad ground or power wire somewhere.
 

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I would expect that perhaps that popping actually goes in time with the engine......
 

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I would expect that perhaps that popping actually goes in time with the engine......
usually I'd agree, but the o/p said "when using accessories or pressing the brake pedal" so thats whats leading me towards bad connections, along with his charging issues. I bet theres one bad connection somewhere with a bit of corrosion acting like a transmitter when voltage appears across it.
 

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Discussion Starter #13 (Edited)
Another update. I added the battery to fender ground back with a 6 gauge wire this time and it seemed to help the volt drop to the cigarette lighter a little. I'm showing 14.2X to the terminals and 14.0X to the lighter now. I checked every fuse (under the dash) while the car was running and it showed 14.2X across all, except for the cigarette lighter fuse, so I'm closer to isolating the power drop.

Also, with the body ground added, I'm still losing a ton of volts with accessories turned on.

I'm going to tear into it more tonight and I'll report back any findings.
 

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Also, with the body ground added, I'm still losing a ton of volts with accessories turned on.

I'm going to tear into it more tonight and I'll report back any findings.
That would lead me to believe you have a main ground issue..

Keep in mind that when doing voltage drop test, they are really only valid on a powered (loaded) circuit
 

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Discussion Starter #15
Little update. I got a 12v meter to keep an eye on what's going on and noticed something odd. If I draw too much power or fall below roughly 1k rpm, the volts drop drastically until I turn off every accessory. The engine also bogs as if the alternator is trying to pump out more power. When everything is turned off the engine picks right back up and goes back to around 14.3v

The cycle I go through in the video is, marker lights > headlights > fan 1 > fan 2 > fan 3 > fan 4 > then reversed.

I'll be switching from a 6ga to a 4ga ground soon. I've cleaned every pos and neg connection in the charging system, including the alt mount.

 

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don't forget the other side of the circuit, the positive feed lines as well. Check all the lugs for signs of corrosion or green residue, especially the connections to the fuse boxes and the big bolt up fuses in the main feed line. The fact volts are disappearing as you load the system suggests a high resistance joint somewhere.
 
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