Do I need an alternator?

[66clow]

Not sure my alternator is charging fully. Should it be replaced? Testing it here are my readings off is the first one and running is the second reading. I think it should be 14 running?

[geezer#99]

Put a load on it running.
Turn on everything you have that uses 12 volts.
THen see what it says.

[ga-stepside]

Rev the engine to about 1000 rpm for a second or so and see of the voltage goes to 14.3v. Start up on GM alternators can be stubborn, sometimes they need a kick start.

[Wrenchbender Ret]

It should run up to about 14 volts if the battery is well charged. If it is not charging the problem could be in the regulator. To test the alt, pull the plug in back of the alt. & put a jumper wire from the term. that the blue wire went to to the hot wire at the black term. You should get a fat blue spark when you do this. Start it up & check the voltage. If the alt is good it will charge infinitly. If it is good your problem is in the reg. or the circuit.

[66clow]

Originally Posted by Wrenchbender Ret

It should run up to about 14 volts if the battery is well charged. If it is not charging the problem could be in the regulator. To test the alt, pull the plug in back of the alt. & put a jumper wire from the term. that the blue wire went to to the hot wire at the black term. You should get a fat blue spark when you do this. Start it up & check the voltage. If the alt is good it will charge infinitly. If it is good your problem is in the reg. or the circuit.

You scared me about getting a fat blue spark. I'm not totally clear about what your telling me to do so I didn't attempt that. I did test the volts by turning on all accessories and this was my results. I also cleaned all my battery connections and alternator connections with no differences. The reason I'm concerned is the truck ran fine but was out one day with it and the battery drained. Had the battery charged and seems fine but concerned I'll be stranded somewhere again. The time it did die I was able to jump it and make it home. Battery is only a couple months old. Alternator is painted like it may be rebuilt or the po just painted it so don't know.

[davepl]

Check the voltage on the big lug at the back of the alternator. 11.8v is indeed too low, but you want to remove a bad connection from the equation by checking what it is right at the alternator output.

If it's still low there, then you likely have a bad internal regulator, bad diode, or something going wrong. If you have a bad diode they often run pretty hot.

[geezer#99]

11.8 with a full load is good.
Likely nothing wrong with your altenator.
Your starting problem was likely heat soak in your starter/solenoid.

[66clow]

Originally Posted by geezer#99

11.8 with a full load is good.
Likely nothing wrong with your altenator.
Your starting problem was likely heat soak in your starter/solenoid.

Could very be it was like 100 that day in Los Angeles. Is there anything to put around the starter to block the heat from the exhaust? I don't have headers. Thanks. I may wait to see if it fails again before replacing. I will check voltage at the alternator to see what that says though.

[jjzepplin]

Autozone will test for free. Just take it off and bring it in.
11.8 volts is too low.
Looks like you still have the external type regulator style so it could be that. It is the black box on the radiator support near your horn. It has four wires going to it.

[Jrainman]

Originally Posted by jjzepplin

Autozone will test for free. Just take it off and bring it in.
11.8 volts is too low.
Looks like you still have the external type regulator style so it could be that. It is the black box on the radiator support near your horn. It has four wires going to it.

If you are not sure Just start truck take positive lead off battery if truck runs without stalling means charging system is ok and you need a battery , if truck stalls out you have a charging issue remove alternator and regulator and do as jjzepplin has posted and then buy the part that is needed and re install

[66clow]

Originally Posted by Jrainman

If you are not sure Just start truck take positive lead off battery if truck runs without stalling means charging system is ok and you need a battery , if truck stalls out you have a charging issue remove alternator and regulator and do as jjzepplin has posted and then buy the part that is needed and re install

There is a test they can do in the regulator or just the alternator?

[truckdude239]

Originally Posted by geezer#99

11.8 with a full load is good.
Likely nothing wrong with your altenator.
Your starting problem was likely heat soak in your starter/solenoid.

that is not true anything under 12.6 is not charging if your reading 11.8 with everything on your are in a discrage mode no charging

[Wrenchbender Ret]

You will get stranded if you keep driving it. I'll try to make my test a little more clear. Pull the 2 wire plug out of the back of the alt. Get a test wire with clip terms. Clip one end to the term. on the alt. that had the blue wire hooked to it. Hook the other end to a hot source like the big term on the back of the alt. When you make & break this connection you should get a blue spark. Don't worry this is harmless. If you get the blue spark this indicates the brushes & rotor circuit in the alt are good. Start the engine. If the alt is good the voltage will steady go up. This is called full fielding. Naturally don't run it very long at this. You can do the same test by pulling the connector off the regulator & put a wire in the blue term in the connector to the red wire term.

[Grumpy old man]

Or you can eliminate all the hassles and install a one wire internally regulated alternator .

And yes that looks like a mechanic in a can alternator ......spray painted not new.

[franken]

A charged battery will be 12.6V or slightly higher. Less and it isn't charged. W/ the engine running the voltage should be higher.
Seems like a lot of work to take pics and post them when typing the numbers is so easy.

[66clow]

Originally Posted by franken

A charged battery will be 12.6V or slightly higher. Less and it isn't charged. W/ the engine running the voltage should be higher.
Seems like a lot of work to take pics and post them when typing the numbers is so easy.

I'm thought we loved photos here lol. I'm just going to tale it out and go to the parts store to get it checked. For around $50 I can replace it and don't have to worry about it. Just had the truck a couple months so working thru the bugs. I think paint was just put on a pig by the po. I'll update ya'll tomorrow. I drove it today and checked the battery running and I was a little less than 12. So that does not sound good.

[Coley]

Before you buy a 'non-refundable' alternator, make sure its not your regulator.
As well....11.8 volts is too low and you are not charging so something is not putting out.
You need to test your regulator as well to make sure its not the culprit. I went through this about 1-2 years ago thinking it was my alternator...and I had it wrong, wherein it was the regulator that pooped its pants.
Quick question do you have a spare 'other' (used) regulator kicking around that you could substitute and retry your existing check at the battery?...this test just takes a few minutes.
Make sure to check before you buy parts.
All good
Coley

[66clow]

Originally Posted by Coley

Before you buy a 'non-refundable' alternator, make sure its not your regulator.
As well....11.8 volts is too low and you are not charging so something is not putting out.
You need to test your regulator as well to make sure its not the culprit. I went through this about 1-2 years ago thinking it was my alternator...and I had it wrong, wherein it was the regulator that pooped its pants.
Quick question do you have a spare 'other' (used) regulator kicking around that you could substitute and retry your existing check at the battery?...this test just takes a few minutes.
Make sure to check before you buy parts.
All good
Coley

Thanks for looking out for my money. I could spend the money on something else. I 'll do Wrenchbender's check as he described tomorrow.

[VetteVet]

Originally Posted by 66clow

There is a test they can do in the regulator or just the alternator?

Pull the plug off the regulator and test the voltage on the brown wire on the end terminal, no., 4 IIRC. it should read battery voltage or near it with the key on. Zero with the key off.

Then plug it back into the regulator and check the voltage on the white wire on the plug on the back of the alternator. Key on 12 volts, key off zero.

If you don't get those readings then the regulator or the wiring is bad. if you do then the alternator is faulty.
You should also get 12 volts on the red wire at the regulator plug and at the blue and red wires on the alternator

Pulling the battery terminal with the engine running is not a reliable check because the alternator may be charging enough to keep the engine running but not enough to power the system.

[66clow]

Originally Posted by Wrenchbender Ret

You will get stranded if you keep driving it. I'll try to make my test a little more clear. Pull the 2 wire plug out of the back of the alt. Get a test wire with clip terms. Clip one end to the term. on the alt. that had the blue wire hooked to it. Hook the other end to a hot source like the big term on the back of the alt. When you make & break this connection you should get a blue spark. Don't worry this is harmless. If you get the blue spark this indicates the brushes & rotor circuit in the alt are good. Start the engine. If the alt is good the voltage will steady go up. This is called full fielding. Naturally don't run it very long at this. You can do the same test by pulling the connector off the regulator & put a wire in the blue term in the connector to the red wire term.

OK I did this test and the voltage did steadily increase. So does that mean it is a bad regulator? Also for Vette vet I do not get 12 volts at the red on the alternator. Not sure if I was doing things correctly to test at the regulator because I could not get a reading.

[prodjay10]

I'd be weary having things tested at Vatozone. The last 4 times I take them a battery for a charge, they tell me it's bad. I put a charge on it myself, and it works fine.

[davepl]

Originally Posted by Grumpy old man

Or you can eliminate all the hassles and install a one wire internally regulated alternator .

Boooo to that. One wire alternators have two things that make them suck:

- They can't self-excite without an RPM flash. That's OK on an EFI car that'll do it every time, but not a carb'd car that starts at and stays under 1500 rpm. You could start your truck and run it for 20 minutes and it'd never charge the whole time.

- The don't remote sense, so they can only charge based on what they see at the back of the alternator, which may not reflect conditions at the battery, at the dash, or anywhere else realistic and important.

I just installed a one-wire setup and took the time to convert it to 3-wire (because the Concept One unit I received had it, but it was plugged off).

They're not the spawn of the devil or anything, and yes they can work just fine, just be aware there are a couple of downsides. Hence the booo.

I'm definitely a big fan of the 12CSI internally regulated ones. I have a part number I use somewhere, I think it's '84 Camaro with AC? Something like that, someone will know if it comes down to it.

[VetteVet]

Also for Vette vet I do not get 12 volts at the red on the alternator. Not sure if I was doing things correctly to test at the regulator because I could not get a reading

This wire is connected directly to the battery via the battery charge wire. If you don't show voltage on it the battery will not get a charge.

Here is the charging system diagram.



See how the red wires connect so that the alternator red wire joins the battery and the regulator wires to charge the battery.

[66clow]

Originally Posted by VetteVet

Pull the plug off the regulator and test the voltage on the brown wire on the end terminal, no., 4 IIRC. it should read battery voltage or near it with the key on. Zero with the key off.

Then plug it back into the regulator and check the voltage on the white wire on the plug on the back of the alternator. Key on 12 volts, key off zero.

If you don't get those readings then the regulator or the wiring is bad. if you do then the alternator is faulty.
You should also get 12 volts on the red wire at the regulator plug and at the blue and red wires on the alternator

Pulling the battery terminal with the engine running is not a reliable check because the alternator may be charging enough to keep the engine running but not enough to power the system.

Here is where I am now. I've tested the various wires and these are the readings. I'm not sure what they mean but thinking the regulator.

The battery off is reading in the 12 range, on it can drop slightly below 12

At alternator red wire off 12, on drops slightly below. White wire off 11.68 on 11.78. Could not get a reading on blue on or off.

At regulator red reads about the same as the alternator on and off. White again same on/ off as alternator. Could not get a reading from the brown or blue on or off.

So I'm thinking the issue is the regulator since I did the full fielding test Wrenchbender suggested and the voltage did increase at the battery. Looks like everything goes thru the regulator and that's why no power thru the brown and blue?

What are everyone's thoughts?

[VetteVet]

Originally Posted by 66clow

Here is where I am now. I've tested the various wires and these are the readings. I'm not sure what they mean but thinking the regulator.

The battery off is reading in the 12 range, on it can drop slightly below 12

At alternator red wire off 12, on drops slightly below. White wire off 11.68 on 11.78. Could not get a reading on blue on or off.

At regulator red reads about the same as the alternator on and off. White again same on/ off as alternator. Could not get a reading from the brown or blue on or off.

So I'm thinking the issue is the regulator since I did the full fielding test Wrenchbender suggested and the voltage did increase at the battery. Looks like everything goes thru the regulator and that's why no power thru the brown and blue?

What are everyone's thoughts?

You have to get 12 volts on the brown wire in order for the alternator to charge. The current from it closes the regulator points and puts power on the blue and white wires. You should get 12 volts with the key on and zero with the key off. If you don't get 12 volts on the brown wire it may have a break in it or a bad connection at the firewall block or the key switch.

As a test you might try running a temporary wire from the battery hot to the brown wire on the regulator plug and check the alternator output wire for 14.5 volts. with the engine running.