[Alpha Pup]

I need some help.
1984 CJ-7, 258

About a week ago we replaced the battery because the jeep would die and not restart without jumping it off another vehicle.
Did the battery disconnect test and it kept running, leading us to believe it was the battery, not the alternator.
The Volt gauge was reading 12V not 13.5 - 14 like one would expect.
The first time this happened was in the morning after driving with the lights on.
We have driven this jeep many times, day & night, and not had a problem.

Here we are again ,,, last night, lights on, 25 minutes in to drive, with the new battery, it starts to run odd.
At a stop light it stalls, tried to restart and it just clicks. Had to get a jump start and drive the last 2 miles home with the lights off to keep it from stalling.

This morning, after being on the charger all night, it starts up fine, we pulled the battery cables off the battery and it keeps running. Turned the lights on and it started to idle a bit off.
It seems the lights are draining the battery down, is our alternator done?
Why wouldn't it die when we disconnected the battery?
We have a multimeter so we can test things, just not sure what to test.

The alternator is a Delco Remy and has a 2 wire plug, brown resistor wire and the red wire split off to a stud terminal on the back.
We did notice the V-belt might be a slight bit loose, but not too loose.

Additional tests this morning:
Unplugged the 2 wire plug - battery connected - still ran
Unplugged the 2 wire plug - battery connected - lights on - still ran
Unplugged the 2 wire plug - battery disconnected - motor died

Are there some additional tests we can do to check output, or the resistance, or anything else?
Shouldn't the volt meter read close to 14 if things are charging correctly?

If it is the alternator, is there a recommended replacement?
We are going to be adding auxiliary lights and an amp for the stereo sometime.

Thank you
AP

[Luckyduck]

easiest thing is to bring it to auto zone and have them test the alt. In my 57 we had a kinda similar problem. we would park it and come back and the battery would be dead. a new battery did not help so we got the alt tested and it was bad (i used the alt tester on the battery charger I have) brought it to a place and they cleaned it or something for $25 and it works perfectly now!

[JeepHammer]

All the 'Battery Disconnect Thing' proves is you can find the connectors.

Take the battery someplace that has a full on LOAD TESTER and have it tested.

If the battery passes load testing,
Then clean the terminals/cables ends and inspect for corrosion inside the insulation.
You will usually find a 'bump' in the insulation if there is corrosion inside.

You can check the alternator output yourself by removing the ignition coil connector and cranking the engine for about 30 seconds, and taking a voltage reading AT THE BATTERY... This WILL require a multimeter or volt meter at the battery.
(This runs the battery down a little)

Then reconnecting the coil connector, and starting the engine and checking the voltage over the first 30 seconds of engine run time...
If the voltage jumps up right after you start the engine, the alternator is working and is self exciting.

If the voltage doesn't jump up right away, and you have to REV the engine to get the charging started, the alternator is no longer self exciting, and you need to check the Exciter circuit (Brown resistor wire circuit),
Or you have problems with the regulator or diode trio inside the alternator.

If the voltage at the battery doesn't jump up to about 14 volts when the engine is revved up to to about 2,000 RPM, then the alternator or it's connections are just plain bad and need fixed/replaced.

[Alpha Pup]

Here is some additional diagnostic information we just measured.
Off - battery voltage - 12.4
Idle - battery voltage - 13.2
Idle - lights on - battery voltage - 12.45 and it seems to drop .05v / minute
2500 RPM - battery voltage - 13.6
2500 RPM - lights on - battery voltage - 12.9

The alternator also has a dedicated ground wire to its cover

[Indy]

Yep, get the alt. tested. It's quick and free. And get it done at 2 different places. I took one I bought off ebay in to autozone and the kid said it was bad. I asked what might be wrong, he just pointed at the needle on the gauge and said "It should be here, but it only goes to there"

I took it to checker and had them test it. Their machine is computerized and shows the tests it goes through along with a pass/fail, and a printout of voltages. It tested good on that machine.

[Mike Romain]

A polished up fan belt can act like that. To test, I take a cold off engine and see if I can hand slip the alternator pulley. If I can and the belt is tight, the belt has gotten polished up and needs replacing. I could eat 3 or more a season when I played in the mud pits. Mud = liquid sandpaper.

A corroded connection can also act like that by not allowing enough amps to cross. The one at the fender solenoid where the battery cable hooks to alternator wire is a good sneaky spot for a bad connection.

How is the body tub ground? There should be a mesh cable running from the engine head to the firewall. Without it the battery can have charging issues, especially when you run the lights.

[Alpha Pup]

Thank you Mike,
We have very good grounds thru out the engine compartment, from the battery to the frame, frame to motor, distributer, starter, body, alternator.

We took some more measurements.
0.0 resistance on the red wire to the starter solenoid. It was a brand new wire so we knew this would be a good reading.
13.3 ohms on the brown wire to ground. We checked this against several grounds.
It is strange that voltage increases .8v from motor off to an 750 rpm at idle, and also increases an additional .4v at 2500 rpm.
This means the alternator is charging, right?

We are going to go get some new battery cables, the ones we have look and test ok, but we are going to replace them any way.
We are also going to take the alternator and get it tested, but not sure we trust the parts store as they just want to sell parts.

Could the alternator have a built in reset, that goes of if it overheats?

[Mike Romain]

Originally Posted by Alpha Pup

Thank you Mike,
We have very good grounds thru out the engine compartment, from the battery to the frame, frame to motor, distributer, starter, body, alternator.

The important one is the body tub. The lights, heater and wiper draw power through the body. If it is missing or ratty, your symptoms will happen.

We took some more measurements.
0.0 resistance on the red wire to the starter solenoid. It was a brand new wire so we knew this would be a good reading.
13.3 ohms on the brown wire to ground. We checked this against several grounds.

Those sound correct. The brown wire is a resistor wire so the alternator doesn't backfeed the coil power when you shut off the key.

It is strange that voltage increases .8v from motor off to an 750 rpm at idle, and also increases an additional .4v at 2500 rpm.
This means the alternator is charging, right?

No, not really. A voltage increase may indicate a power increase, but not always. Your 2500 rpm reading is too low, it should be over 14 volts, 14.4 preferably, that is why I thought slipping belt.

We are going to go get some new battery cables, the ones we have look and test ok, but we are going to replace them any way.
We are also going to take the alternator and get it tested, but not sure we trust the parts store as they just want to sell parts.

See if they give the same top voltage reading. If they do, then believe them when they try to sell you the new one you may need.

[Alpha Pup]

Thank you, I've been reading this forum for almost a year and have to say, and my dad agrees, you are always right on.
Thanks

[Mike Romain]

Originally Posted by Alpha Pup

Thank you, I've been reading this forum for almost a year and have to say, and my dad agrees, you are always right on.
Thanks

You are welcome. I do have my moments though, still things to learn. :-)

[Alpha Pup]

We just got back from Auto Zone.
The alternator was turning 14.5v and was at the top end of the "green" zone.
The guy said it was good.

We are going to reinstall it and put in the new battery cables and see what happens.

The guy said there might be a drain on the system when the lights are on.
My dad just looked at him and said "of course there is". He thinks the amp output is not high enough for the jeep.

[Mike Romain]

Now you just have to find the bad connection....

[crusty75]

A quick and easy shot in the dark: Take a minute to run a dedicated ground from the battery negative to the grill. Sometimes, even though the body is grounded well, sometimes that ground has a hard time making it to the grill, which is what the lights ground to. See if that helps with the meter readings.

A second thought, you're not by chance running upgraded (from the original type) halogen headlights (such as silverstars or such) without using a relay are you? Lots of times running a halogen upgrade w/o a relay will work fine for a while, then begin to cause problems as your headlight switch slowly croaks...

[Alpha Pup]

Thank you, it does have a strong ground going to every main component and structure on the jeep.

We have the alternator back in, the belt is new and tight. New 4 ga battery cables.
Here are the readings.

Off - battery at rest - 12.35v
750 rpm idle - everything off - 13.40v
750 rpm idle - only electric fan on - 13.00v
750 rpm idle - only lights on - 13.00v
750 rpm idle - only high beams on - 13.00v
750 rpm idle - electric fan and lights on - 12.50v
750 rpm idle - electric fan and high beams on - 12.30v

2500 rpm - everything off - 13.95v
2500 rpm - electric fan and high beams on - 12.65v
After shut off, the battery is at 12.65v and in 10 minutes settles at 12.35v

The alternator is stamped with the following:
1105079 42A
4C30 12V NEG

We thought maybe it is a 42 amp alternator.
Until we looked it up, this seems to state it is a 63 amp
www.delcoremy.com/LiteratureDownload/Documents/Quick_Reference.pdf

There is no current draw while the jeep ignition is off. The lighting wires don't have any shorts, the wires are not hot, the grounds are overkill.

Things running both times when the jeep stranded me
Lights - running and headlights
Stereo - no amp
Electric engine fan
Fuel injection computer

Should we be looking for a 140 amp alternator?

[OldSailor]

If your present alternator is a 42-amp alternator, it is too small. The OEM alternator was a 63 or 65 amp alternator. The latter should be sufficient as long as you do not have large aftermarket loads on it, like big stereos, extra lights, winch, etc. If you have those extra loads, then get a 100 or110 amp alternator conversion.

BTW, your voltage readings at 2500 rpm with normal loads on it are too low. At 2500 rpm, with headlights on, it should still be between 13.8 and 14.2 volts.

So, there are really only three causes:
(1) Your alternator is not putting out enough current, either because it is bad or because it is the wrong alternator/
(2) Your battery is bad and is comsuming too much current from the alternator. The solution is to fully charge the battery off the vehicle and then get it load tested.
(3) You have a bad high current connection or cable.

The only voltage reading that really looks bad is the one at 2500 rpm with fan and high beams on. It should be higher.

When you got the alternator tested, and they told you the voltage it was putting out, did they tell you how much current it was producing? If it is in fact a 42-amp alternator, it would put out the correct voltage on a test setup, but it wouldn't put out enough current for your application.

You need a 65-amp Delco alternator on there.