alternator problems
 

back in may i had changed my alternator for a remanufactured one from Autozone and it worked up until 2 weeks ago when it went bad again. went back to Autozone, got another remanufactured unit and now it went bad. this time, the battery light comes on only when I'm about 2,000-2,500 rpm depending what accessories are on. is this an alternator problem or something else? AutoZone was giving me a hard time saying it's not the alternators but something with my car making the alternators go bad.

both units were remanufactured valeo 140 amps

A bad battery can cook an alternator.

Testing Required for answers
 

Lets get some real information before you run back to the white box auto parts retailer with another "failed" unit.

Has the charging system been tested on your vehicle?
What is the voltage at idle, 1,500 and 2500 RPM? What was the amp output at 1500 rpm?

Has the starting system been tested in your vehicle?
Starter amp draw?
Battery Load tested (volts and amps?)
Battery voltage at rest (key off)?
Battery voltage at idle?
Battery voltage at 1500 rpm?

These simple tests will tell anyone with auto diagnostic skills, what is going on. Everything else will be Scientific Wild Ass Guess > SWAG, based on personal experiences and other general guessing.

Notes:
Cheaply manufactured Alternators have approx 32% failure rate. A cheap Alternator with a cheap volt regulator installed makes that rate low. In a price driven world of remans, the installer is the first and last step in quality control. :wow:
Many posters have experienced what you are going through. It was their solution to replace the offending alternators with new Bosch units that resulted in solving their issues. IMHO the volt regs are the weak point on most of the white box alternators being sold at the auto part chains.

Stick with OE or OE Aftermarket as the original one lasted 100k.

voltage at idle is 13.5v-13.3v
at 1500rpm its 13.9v-13.7v
at 2,500rpm if the light isn't on about the same as 1500rpm
if it is on drops to low 12v.

i didn't check anything else

and my car had a valeo in it to begin with

Yup, Valeo is the only listed supplier for the E53 3.0i 140amp alternators.

I assume it's the 6cyl as the 8's all had Bosch water cooled ones AFAIK ($$$).

I've read a lot of people go through a few replacements with remans.

As already posted I would check the battery is still good. Other than that, with the symptoms as you describe, I would be suspecting the alternator myself.

The battery is only a couple months old

Try checking the BST (Battery Safety Terminal)

Could be faulty?

These links mught help.

https://www.youtube.com/watch?v=c26Jq1O1m0M

https://www.youtube.com/watch?v=s-XO98LOa3Q

I had an Autozone's Duralast battery that was just a day old when it tested bad. Don't assume that because you replace the battery it must be good.

Thanks for the test numbers.
voltage at idle is 13.5v-13.3v
at 1500rpm its 13.9v-13.7v
at 2,500rpm if the light isn't on about the same as 1500 rpm
if it is on drops to low 12v.

Based on the fluctuation above idle I would return the unit, stating that there is a loss of charging state at hwy speeds and demand a replacement. Then I would make them test the unit before leaving the store. The test needs to show Voltage and total amp output at multiple RPMs. It can not be just volts as that will not show total output.

The numbers show that at idle your alternator is charging correctly.
ANY fluctuation off idle and into higher RPM shows a slip ring, windings loose, or brush contact issue. VERY common issue on rebuilts that have not been cleaned, ground flat, and paint over spray on the contact points. This problem with rebuilt units has been a re-manufacturing issue since the 60's as the cost of quality control and true manufacturing brings the cost to the end user close to new prices. That is why there are so many short cuts and defect units. Once you had the chance to bench test a few defects, you will notice that all some do is clean, paint, and slap a regulator on them after a quick cleaning of the stator along with a bushing or two. A REAL BAD PROCESS but one that delivers a cheap unit with controllable defect rate.

If it was my vehicle or a customer vehicle, I would install a new Valeo unit of the highest AMP output I could find, as it would be 100% new and bench tested. In your case as you are doing the labor each time, you get a simple choice...price or performance reliability.

Next test is the battery condition. Attached is a great write up by a community college tech teacher showing proper methodology and metrics.
Note: You can simulate a "load draw test", by turning on every accessory (don't forget the rear window defroster) on high for a 60 sec hit. You will NEVER get to 250 amps but it will pull the surface charge off the battery for a backyard quickie test.

The tests are always: Key in your pocket, test at battery terminals not under the hood. Then RE-test under the hood to confirm that the wiring and connections are at 0 resistance (or close enough).

Tip 1: Test the large positive jump point on the firewall to make sure it is tight. Multiple people have experienced fluctuations of start/no start issues from this connector.
Tip 2: Check the wiring harness from the alternator and starter for breaks in the insulation and wires chaffing.

Search "VOLT DROP TESTING" and check the cables and grounds in and around the trunk mounted battery.

Bottom line: Test all and confirm "KNOWN GOOD" what is left is what is bad.

Good luck and hopefully this is helpful.