I am having trouble keeping the battery charged. When I have the alternator tested it passes the test but when the engine is running its only putting out 11.5v to just above 12v. Is there something else that is bad.

 

Are you getting 11.5 from the alternator posts? Is this with the connector connected or disconnected?

Try taking the connector off and checking it that way, see if you still get 11.5

You should get 13-14V from it without it loaded, if you are still getting 11.5, then your alternator should be replaced.

If you are getting 13-14V out of it unloaded, you most likely have a ground, short, or a corroded connection somewhere in the line that needs finding

EDIT: you should be testing both + and - at the alternator itself, do not use a chassis ground when checking your alternator voltage.

 

I am getting that voltage from the datalog so that means from the computer. I have not checked voltage at the alternator. Is there a voltage regulator in the wire harness or is it just internally in the alternator.

 

What should my voltage be at idle. Right now I'm looking at the log it say at 1825rpm I'm making 12.7v. The highest it gets is 13.0v at 975rpm. Also does an under drive pulley have anything to do with it being low.

 

Under load it should be more around 14v but with an aging alternator 13v is totally understandable. I would replace it anyways and not worry about it. If your battery is getting a few years old have it tested for its cranking amps. That is a good indicator if you need to replace your battery or not. Usually its a smart idea to replace both the alternator and battery together because if one goes bad it hurts the other. For example your alternator is bad, your battery now suffers a low maintenance charge from it. You replace your alternator and now your battery is straining your new alternator to come back up to its original capacity.

 

An Underdrive pulley on your alternator would definitely cause issues with voltage output at low RPM. That causes the alternator to spin less

You should be producing 13.7-14.3v @ 1500RPM At 800-900RPM, you should be expecting at least 13.0V, which you have, and that is curious by itself, as you should see peak voltages at higher RPMs, not lower. I'm betting your voltage regulator inside the alternator is not behaving.

 

Hmm ok. Well could that be why I keep having to replace the battery's. I just replaced the battery last week and since the alt wasn't charging it the battery has a low charge. Only good thing is that the battery has been under warranty so free replacements. I will have the alt tested tomarrow to see what's up

 

You really should check the voltages directly out of the alternator yourself with a voltmeter before removing it and bringing it in for a test

There could be bad connections / shorts / grounds / corrosion in the wires and connections between the alternator and the Datalog. This would mean that your alternator could be putting out proper voltages ,they're just not reaching their intended target at full strength.

 

 

Had the alternator checked it passed checked the battery it was bad. How can a 2 week old batt go bad that fast. Do I need to look for shorts in the wires. Is there a way to see if there is a short by looking at resistance or something like that.

 

I got a bad battery once also sometimes they are defective right from the get go. Drive her for awhile and let us know how you are doing.

 

A slow short could definitely kill a battery. You can take resistance readings, but it's not generally a "OH THERE IT IS!!" solution, it takes some interpretation.

First, disconnect the battery, and check all fuse block points to ground. Pull each fuse, and probe BOTH leads while having your black lead on a chassis ground point. Make sure to have all light switches turned off.

You will most likely see some readings that are not open, but that's not always indicative of a problem, as you can read the resistance of the full circuits. You should reference the wiring diagram to see what you are probing, so you can figure out if it's "normal". (i.e. most motors / light bulbs will read 0-50 ohms from hot to ground)

Here's some links to wiring diagrams for your car:

http://austinthirdgen.org/mkportal/m...ine_wiring.gif

http://austinthirdgen.org/mkportal/m...ody_wiring.gif

http://austinthirdgen.org/mkportal/m..._continued.gif

 

Ok I'll have to take a look at that. So today I got the new batt installed checked the voltage on the data log it was 13.8 at 900rpm. I will have to keep an eye on the voltage to see what it does. Still haven't driving it to see what it does.

 

This is getting old fast. Drove the car to work drove great the volts on the gauge would go back and forth from 13.5 or so to just above 12 or under. When I left work car started fine. Woke up this morning batt is dead. In a matter of 5 hrs. I don't get it

 

Could the alt have a bad ground. How does it get grounded anyways. Is it through the wire harness or the mount but then the mount is aluminum so idk. What about the rod that comes out the back of the alt to the headers I don't have one is that the problem.

 

Sounds like maybe a bad voltage regulator inside the alt. I have had a few checked in the past that passed but they would work good for awhile and then act up. I would take it down tell them whats going on and have it checked again.

 

Every time I test that alt it tests good. I checked voltage yesterday everything was coming up 14.2 or 13.8. That's at the batt and coming off the alt.

 

One time I had a sticky horn relay that would drain my battery the po cut the wire to horns.

 

I'm having the same problem but my battery takes a couple of days to drain. Tonight I did a simple check to see if the alt was charging the battery. Just started the engine and watched the voltmeter. It had 13v at start up, turned the headlights on and volts dropped to 10v. Pressed the brake pedal in and the volts dropped enough to stall the engine. Going to rebuild the alt this weekend. Give that a try with a fully charged battery and see what you get.

 

i've got the same problem, have you had any luck yet?

 

Not yet. Glad I'm not crazy. It's like the car is moody for some reason. Works fine one time is pissed of the other.

 

Must be pretty common. Went and started the car this morning and it fired right up and the alt was charging the battery. Started it this afternoon and the battery went dead in 10 min. Borrowed a good alt from my brother to get me by till I get some time to rebuild mine.

 

Any of you guys checked the voltages at the alternator connector yet? Should be battery voltage on pretty much all of the wires at the connector (with the ignition on... brown and tan wires won't have power with the key off).

 

I checked power at Batt and it was good with car running. I have not checked the volts right at the wires at the alt but when I get the alt tested it tests fine.

 

From what I've seen, most stock regulators are designed to hold the system voltage at or just barely over 14V (mine is usually 14.7V if the regulator and such is good). If that isn't what you're getting at the battery and the alternator "tests good", then the wires at the 2/3-wire connector need to be checked.

A lot of people lately are having problems with the brown wire at the alternator connector. This wire runs to the (or A) coolant fan relay, where it gets power off of the C/H FAN fuse, which is only hot with the ignition on. This wire tends to get hot due to slight overcurrent and melts some of the insulation near the fan relay, which allows corrosion to set in due to humidity, which makes the overcurrent problem worse. This wire is the primary "sense" wire which turns the regulator on and off.

 

So should I try to clean the connector at the alt and see if that's the problem. I don't have the fan relay hooked up so I don't know if that makes a difference or not.

 

That would also explain why sometimes it's a good current and others it's not. But does it explain the dead batt after sitting for a little while.

 

It doesn't matter if the fan relay is installed or not as the wires are joined at the terminal in the relay connector. If the wires at the relay connector have melted part of their insulation off and there is a short, that may explain the dead battery.

What you can do is to disconnect the negative terminal of the battery and hook a multimeter between the cable and the battery. Set the meter to read current (amps) and check the reading with the doors closed, hood light removed (if you have one), and everything off. I believe the acceptable battery drain with everything off is supposed to be 2 amps or less (ECM backup, radio presets and clock backup). If the drain is higher, pull one fuse at a time out of the fuse panel until the current draw is under the limit. The fuse that drops the current to acceptable tolerances is the one for the problem circuit. This will also include the 2 fuses (MAF system, MAP system only has 1) under the hood, probably by your battery (Camaro) or by the air canister/filter assembly and charcoal can (Bird).

 

Ok I'll have to check that out. Thanks.

 

ok i have found one problem. The connector that comes out of the top of the alternator is bad. When i move it with the car running and the headlights on they dim and get brighter. So once i am able to replace it that might help with the odd batt voltage, but will that help with the batt dying?

 

any idea of where to buy a pigtail for that connector

 

Parts store may have them special order. Or you can try eBay. Or a junkyard. Just make sure you get one that matches the one you have (there's 3 wire ones, 4 wires, and 2 wires).

:edit: As for the battery drain, the only way to find out is to replace the connector and do the test I outlined above...

 

Rockauto.com to the rescue. Question my connector is a 4 pin 2 wire connector all the ones i am seeing have at least 3 wire 4 pin connector. whats the differance

 

You won't connect the tan wire... The brown one and the red one get connected, but the tan is extra. Most of the older harnesses have the 3-wire connector, but somehow GM changed the harness to delete the tan wire (which was actually redundant anyways, but the alt won't function without it in the older models).

 

sweet thanks sounds good to me. i hope this fixes this problem

 

Don't cut your existing connector off right at the plug... Cut a few inches of wire off so you can actually tell what wire is what color, which requires cutting back a bit in the harness.

 

Yea that was the plan it will put some slack on the wiring harness.

 

I finally got my alternator apart. The plug on top was very corroded and the power wire was bare about half an inch from the connector. The rectifier bridge was partially melted and I can see burn marks on the diode trio. Got a rebuild kit comming.

 

Yea sounds like this might be a common problem. Guess we will just have to wait and see If it's the fix or not.

 

Alright replaced that connector so there is a good connection. But still running at 13v or so. I noticed that when I turn the headlights on the volts gauge drops to 12.5v and when the fog lights are on it drops to 12v. It could just be where the gauge is grounded I have to check that but could the relay the is running the headlights be bad and is sucking all the power.

 

There are no relays for ANY of the lights on the car. None. Only relays in the chassis harness (body controls, not engine) are for the horn, hatch release (if equipped), and the power locks.

Check the fan relay next. A bad connection on the brown wire is the next thing to check.

 

Really no relay for the fog lights. My headlight and fog lights are connected to a factory installed relay factory as far as I can't tell.

 

Fog lights (always forget those as I've pretty much never had them) yes. Headlights, NO. They're run directly off of the switch (until 1993, IIRC), which is why the switches burn out after a while due to the current. Which is also why the headlight switch has a built-in circuit breaker (to prevent over current in the headlight circuit due to a short or whatever). The reason the headlights' high beam circuit turns off the fog lights when turned to high beams is because the fog light relay coil is turned off when the dimmer is tripped to high beams. And yes, you can run the fog lights WITHOUT the headlights even being turned on (but the parking lights MUST be on for the fogs to work).

 

Ok good I'm not crazy lol. Yea I understand how it's wired and that damn switch does get really hot. But shouldn't the relay cut back on the voltage and amps that it draws. I don't have the fans wired to the harness I have two 30amp switches running them. I know that i need relays on them working on it. Could I be over drawing from the batt and that's why the batt keeps failing or do I have a much bigger problem.

 

The alternator is still connected to the brown wire in the factory primary fan relay connector, which draws power from the FAN fuse in the fuse panel. Make sure you have no problems with the fan stuff you added first (to check for current draw/shorts) and then find the factory fan relay and measure the voltage on the brown wire with the ignition key on. The volts at the fuse, relay, and alternator connector SHOULD be the same. If not, then you should check the wires at the relay for burned insulation, which is indicative of an overcurrent situation (only fuse on the power side of the circuit is the 30A fusible link on either the starter or junction block as opposed to the FAN fuse on the control side).

 

Just tested my batt again. It came up bad batt. I think it keeps getting shorted out. It was only able to hold 12.11v. I wounder if it's the batt that is just not well made or is the wiring killing the batts.

 

When I check for draw from the Batt what setting do I need to have my volt meter set at

 

With my meter set at DCA and the positive cable is attached to battery neg is disconnected and the meter wires are between the neg cable and neg post. Looks to be drawing .263amp. Does that sound right.

 

I appear to be having a similar problem with my 88 Trans Am. Did you ever figure this all out?

 

no i have not but i did start disconnecting the batt cable everytime i turn it off. its the biggest pain in the butt but it hasn't killed the batt yet starting it is a pain since the com gets wiped