Silverado Alternator not putting out proper volts - Already changed the alternator...

[someday31]

Originally Posted by consultIII

they seem reasonable from truck to truck...honestly, have never checked there before (gm doesn't have spec's at these terminals that I have found). Was as interested as you to see what they would be.

If I leave now, I'll be in NY by tesday...keep that beer cold!

Ok guys heres a thought, my plan for Sunday....I am going get another battery out of another vehicle and then hook it up to the output of my truck alternator. I then would just ground it to the frame so nothing else is hooked up to the alternator. I want to see what volts I get...I will do that with the harness hooked up and with me just powering the terminal that the ecm powers. If this gets me my 14.77 volts with the harness hooked up then that would mean to me that my problem is after the alternator...ie the starter, fuse box, etc.

What do you think? Is there any reason the alternator shouldnt charge that other battery...it would be like bench testing it, but would allow me to see voltage straight from the alternator!

Nothing will please me more than to go back to the chevy dealer one day and tell them that we figured it out and that their $93/hr techs couldnt! They just tell me I have a ghost and have to live with it! lol

[someday31]

I did my test as mentioned above...I actually got lower voltage than when hooked to my truck. I think thats because there wasnt enough load and the alternator sensed it so didnt put out as much, I got 13.85 volts. Anyways....im out of ideas at this point guys!

Time for a beer and throw up the flag, I give up!

[rhandwor]

I had the same problem on my Silverado. I didn't do the testing you did but the problem was a crack in the battery leaking battery acid. I originally cleaned the terminal and put it back on it worked fine for a week or two.
I pulled the battery saw the problem and purchased a new battery. I dipped the terminal end in baking soda and water. After the acid neutralized I cleaned the end thoroughly. The bolt was pitted bad and I put in another good bolt.
The charge rate on the ammeter went from 14.2 to 14.5 and dropped after the initial drain was replaced.
If you recently changed anti freeze this is an insulator. Clean with contact cleaner brush and reinstall the terminals.
You can take the alternator to a shop and have it bench tested.

[someday31]

Originally Posted by rhandwor

I had the same problem on my Silverado. I didn't do the testing you did but the problem was a crack in the battery leaking battery acid. I originally cleaned the terminal and put it back on it worked fine for a week or two.
I pulled the battery saw the problem and purchased a new battery. I dipped the terminal end in baking soda and water. After the acid neutralized I cleaned the end thoroughly. The bolt was pitted bad and I put in another good bolt.
The charge rate on the ammeter went from 14.2 to 14.5 and dropped after the initial drain was replaced.
If you recently changed anti freeze this is an insulator. Clean with contact cleaner brush and reinstall the terminals.
You can take the alternator to a shop and have it bench tested.

I actually have put a brand new battery in, have changed it 3 times in the past few weeks. I have changed the battery terminals tonight and no change. I really dont know whats left to do!

[98chev]

Hmm this is wierd. I have a similiar problem with my truck. It is a 2003 Z-71 5.3. with all accessories on the voltages drops to 12.4 volts (checked with meter) as i turn off stuff the voltages comes back a little for each one when everything is off voltage is around 14.4 this is with truck idle or reved up hot or cold but worse when hot. now that it is winter i dont notice the problem as much. took truck to alternator shop benched tested and tested on truck amperage output was good just voltage drops. tried different alt. same thing new battery same thing. The truck is never dead so i am living with it but just doesnt seem right.

[j cAT]

Originally Posted by 98chev

Hmm this is wierd. I have a similiar problem with my truck. It is a 2003 Z-71 5.3. with all accessories on the voltages drops to 12.4 volts (checked with meter) as i turn off stuff the voltages comes back a little for each one when everything is off voltage is around 14.4 this is with truck idle or reved up hot or cold but worse when hot. now that it is winter i dont notice the problem as much. took truck to alternator shop benched tested and tested on truck amperage output was good just voltage drops. tried different alt. same thing new battery same thing. The truck is never dead so i am living with it but just doesnt seem right.

you must check this out with the alternator in the vehicle using an amprobe to measure the alternator current...with the engine running for about a half hour and the engine is at normal temp measure the current . it should be around 60-70amps with all electricals on.. if it is above this turn the electrical devices off one at a time to find out which one is drawing the excessive current....

now if the voltage drops with this amount of current [60 AMPS] check the voltage at the alternator terminal as this alternator wire may be defective..

normally when the alternator cannot supply the correct output current with OEM DEVICES , this is because the current is not full wave rectifcation...it is with pulses not a solid current stream..

since you just get 12.4volts at battery and the battery and alternator have been replaced with new you need more testing to determine whats drawing excessive current..or defective wiring/grounds..

[someday31]

Originally Posted by 98chev

Hmm this is wierd. I have a similiar problem with my truck. It is a 2003 Z-71 5.3. with all accessories on the voltages drops to 12.4 volts (checked with meter) as i turn off stuff the voltages comes back a little for each one when everything is off voltage is around 14.4 this is with truck idle or reved up hot or cold but worse when hot. now that it is winter i dont notice the problem as much. took truck to alternator shop benched tested and tested on truck amperage output was good just voltage drops. tried different alt. same thing new battery same thing. The truck is never dead so i am living with it but just doesnt seem right.

Yeah this is the first time I havent been able to solve a car issue like this! I am planning on going to alternator repair shop this weekend to see what they have to say about everything!

[consultIII]

re. battery low state of charge!! Does this apply??

when you shut your truck off at night are you leaving key in the igniton? This will keep the bcm active waiting for your next input and drain the battery overnight. Even if the key is in the off position but inserted into the cylinder.

[someday31]

Originally Posted by consultIII

re. battery low state of charge!! Does this apply??

when you shut your truck off at night are you leaving key in the igniton? This will keep the bcm active waiting for your next input and drain the battery overnight. Even if the key is in the off position but inserted into the cylinder.

I dont leave the key in mine ever. I live in NY afterall. lol

[RahX]

Ok, so like everyone else has said, the alternator is behaving normally. You've replaced it so that eliminates the alternator (mostly) You've replaced the battery, that eliminates that. Have you done a voltage drop on the ground wire to the body/frame/engine? From the positive battery terminal to the positive on the alternator? I would agree with the thinking that you have an intermittent drain on the battery. The only way you're going to catch it is if you get lucky or watch it for a long time. A higher amp alternator isn't going to do anything for you. Like others have said, your battery can only take so much of a charge. Usually 14v@20-30 amps is a very heavy charge. If it stays that high for too long, the battery will boil the electrolyte and burn itself up.

[rhandwor]

Some items to check red fuse able link at starter solenoid.
10 amp fuse left bussed electrical center lower left side of dash.
Ground left radiator support bracket.
Ground 4.3L right front of engine.
Ground 5.3L left front of engine.
Ground mid bussed electrical center{center under left side of dash} right rear of engine.
Look at connections in splice pack plastic cover close to battery on positive cable.

[j cAT]

Originally Posted by RahX

Ok, so like everyone else has said, the alternator is behaving normally. You've replaced it so that eliminates the alternator (mostly) You've replaced the battery, that eliminates that. Have you done a voltage drop on the ground wire to the body/frame/engine? From the positive battery terminal to the positive on the alternator? I would agree with the thinking that you have an intermittent drain on the battery. The only way you're going to catch it is if you get lucky or watch it for a long time. A higher amp alternator isn't going to do anything for you. Like others have said, your battery can only take so much of a charge. Usually 14v@20-30 amps is a very heavy charge. If it stays that high for too long, the battery will boil the electrolyte and burn itself up.

although this guy still has battery charge loss ,,,, this post has very detailed info that is great reference data for others , that have issues or need training on how this all works.............

[rhandwor]

Originally Posted by old_master

Alternator output voltage and amperage is varied and controlled by the PCM.

Wiring at the alternator:

The red wire comes from the battery and through a fuse link and then to the output terminal of the alternator. It should show battery voltage at all times.

The dark blue wire goes to supplemental brake assist.

The brown wire goes to the PCM for the charge indicator control.

The grey wire comes from the PCM and goes to the voltage regulator inside the alternator. The PCM monitors voltage and load on the battery and determines what the charge voltage should be. It then sends a signal, using a duty cycle, to the voltage regulator. The greater the load on the battery, the longer the duty cycle.

"Old School".... ideal voltage, in a perfect world, was 14.2 volts. Now that the PCM is in the equation, "Old School" is out!

While I don't have a 2003 wiring diagram. I looked at a 1999 Mitchell and a 2000 Alldata wiring diagram. Mitchell says the battery light bulb if burnt out will cause problems. Apparently it is still used to excite the field. On my 2000 this bulb is the message center. It goes on stating to ohm wires going to the IPC {instrument panel cluster} check the ground for the circuit and fuse for this item. Mitchell says to replace after all checks are done. Apparently 13 to 16 Volt at 2500 rpm lights,defroster,close to a full load. Alldata shows a logic and states the computer monitors this circuit to regulate voltage. Is this still true for the newer models?

[someday31]

I took a chance bought this harness

http://www.zzperformance.com/grand_p...=517&catid=107

This resulted in no change of output, not sure what that means. Tomorrow I'm heading to a alternator repair place, will let you guys know what that results in.

[someday31]

Ok so I am finally making a little progress in figuring out my issue. I brought one of the alternators from my truck and had the shop bench test it. They were only able to get the 14.10 volts out of it like I am getting! Then they proceeded to test one of their rebuilts that fits my truck and they get 14.77, which I use to get! So the guy told me he thinks I have the newest style that fits the late model trucks with a lower voltage setpoint.
Anyways I then decided to buy a different alternator to try from advanced auto. I put that in and I finally got the 14.80volts...at first... then as i drove it slowly retracted down to the 14.10 volts. So what does that mean, whats going on.... is it temperature sensor dropping volts as it gets warmed up? I would think my volts would stay the same, just amps would drop as warmed up.
Btw brought the truck for a test and its still getting good battery, low charge!
Does anyone know the difference between the AD244 and DR244 alternators....