Okay here is my problem, all my gauges when my car is running in park are fine, but as soon as i drop it into drive the volts drop down to the red line, if i put it back in park it goes back up to 13 volts. any ideas?

 

If it's just the charge indicator... Loose belt, bad tensioner or bad alternator

 

I actually just changed the tensioner, when i went to try and pull the pully back to remove the belt it was really hard to move then there was a loud snap in side of it so i went and replaced it., now the mark for belt wear is it when the arrow and the line, line up the belt needs to be changed?

 

The belt marks are for proper belt sizing.. Does the belt seem like it's loose ?

 

doesnt seem to be loose but before i changed the tensioner the where the belt came up around the alternator then under the tensioner it would bounce left and right, i read that if you can turn the alt pully the belt is worn or glazed and should be replaced. I still just cant figure out why this darn volt gauge drops only when thrown into drive.

 

If you can turn the alternator pulley with the belt on and it's serpentine regardless if the belts worn out or glazed the belts the wrong one , It's too long... It's a extremely good chance that's the problem. If not the alternators no good. Sounds like wrong belt to me though

 

Well i tried turning the alt pully its pretty tight it actually turned the belt with it when i pushed really hard, i attatched a video link which shows how the volt gauge acts when accellerating...ill describe it since the resolution is ok. but I tried to keep the file size down to 1mb.

Volts are @ 13 when in idle
When i start to drive, all of the sudden the volt gauge drops
down almost to eight causing the interior dash lights/headlights/tail lights to flicker.

**Click on the link with the right mouse button and click Save As then after the download just double click the icon**


http://members.aol.com/gmfbodies/gauges.mpg

 

First thing to do to troubleshoot is fully charge the battery. If the batt is low either series Delco unit will not charge correctly. 13 volts output with a properly charged battery is too low. Average output should be around 14 volts. Based on your stats it's very possible the alt brushes are worn or there is an issue with the regulator. Assuming the drive belt is within specs I would use a step by step course of action to diagnose.

 

Put a voltmeter on the big wire on the back side of the alternator and check what the voltage does when this problem occurs. from what the MPG shows it looks like the alternators bad

 

okay, i went and had my alt tested at kragen they said the Stator and diode was bad so I bought a autolite 105 amp alt. charged my battery and installed it, when its idling now it shows 2 hash marks above 13 but still when driving the voltage jumps up and down.

 

Like it was before or diffrent ? I have been a tech for many years and had lotsa a defective alternators

 

Its doing the same thing, except at idle instead of the volts being exactly at 13 its 1-2 notches higher. Someone had said to check the engine to firewall ground if it was bad/missing or whatever could that cause this problem?

 

What are the circumstances when you see a voltage change? Is the changing very erratic or does it slowly seem to wander? An erratic change indicates possibly a wiring or ground problem. Different reading at different times may just be indicating differences in demand from the accessories. E.G., if the fan if its electric when it kicks will cause the voltmeter to drop a lot and slowly come up. The meter will not always show a constant charge as the battery comes, up it will start to come down as the alt throttles back. Check the batt cable connection at the block, as well as any other wiring. Don't forget to check the starter solenoid junction as it is also a source of problems if its loose or corroded.

 

Okay so basically what happens again is,when the car is sitting at idle the everythhing is ok, as soon as i hit the gas the the volts drop from 13 to about the redline area at 8 then go up half way it just all over the place I attatched a mpg showing what happens. But while driving the volt gauge is going up and down, but when i stop it evens out. may not be at 13-14 but it doesnt jump around.

http://members.aol.com/gmfbodies/gauges.mpg

 

Ok.. here is the deal.... If your charging system is working and your sure the belts not slipping, Say there was an electrical problem in the wiring other than the alternator and or wiring, the lights wouldn't dim unless it's a problem I shal list for you below. You are looking at a voltmeter on the dash fed from the alternator. Here is how things work..

You have 2 wires on a single plug into the alternator and you have one large wire on the back of the alternator. The large wire feeds the battery. the little ones .. one has voltage all the time the other is key on voltage.

Using a test light check the two wire connector that goes into the alternator. One lights with the key on (12v) and the other lights even with the key off. Now, hopefully you have a voltmeter.

This is a voltage drop test to test the cables or voltage feeds to the battery for weaknesses or resistance. No wires on the back of the heads should effect alternator output if my memory works right tonight.. LOL
With the engine running....
Test Negative battery cable : Measure with a voltmeter from the negative battery cable end as close to the battery post as possible to the alternator case. Shoud be no more than .5 volts. If it is you have a problem with the negative cable and or connections.
Same with the positive.. Measure from the big lead on the back of the alternator to the positive battery post or cable end. No more than .5 volts allowed here either. If both test good than you don't have a ground problem or a feed problem from the alternator. I think the feed wire is like 20 inches from the alt to the battery. If this passes.
Turn engine off and the key back on... Measure the voltage on the back of the alternator. ( Big Terminal ) Then measure the voltage on the little wires with the key on. They should all be close to the same. If one of them is a lot less then turn the key off. Is the one that had alot less without power with the key off ? If so than it's ignition switch and or wiring related. if all ok then run a wire to the large terminal on the back of the alternator and test drive. Does voltmeter change just like dash ? If so replace defective alternator