Alternator question

[Superdave]

Has anyone else had problems with the CS130 alternator and higher RPM's?

I ask because i'm about to install my 3rd in 2 years.. i've put maybe 1000 miles on the last one and now it's sitting at about 12.8V while running.

my car regularly sees 6500+ RPM's which the stock 3.1 would hardly ever see..


thanks for any info...

[1988GTU]

Whats failing in the alt? Bearing, regulator?

[Superdave]

regulator...

this one was fine last week (via the datalogs) it was holding around 13.8v.. at the track last night my logs showed it down to around 12.8v

I took it out and had Autozone test it, then Orileys and it passed at both places.. I checked all the connections and everything is fine as well.. wtf

[mfuller]

Are you sure it's the alternator and not the battery? Have a bad ground anywhere? Simple questions, I know......

[Superdave]

Battery is about a month old, all the connections are good.

[Joseph Upson]

Not sure if it's a problem Superdave, I don't know much about the alternator series but my datalogs for the 3900 hoover around that range according to the datalogs. I thought I had damaged the first alternator with a direct 12v feed but it tested good as well as the replacement and I discovered at that time the 3900 alternator is ON by default requiring no voltage input and when the plug terminals are connected to eachother it turns the alternator off. When this is done briefly while the engine is running you can hear the alternator make an unusual noise indicating it is turning back on. I never had a problem on test drives.

I had the alt for the 3500 tested and it required the 5v input to turn it on. I'm not sure but I suspected the regulator in the 3900s alternator is a bit more sophisticated in that it can regulate for voltages less than 14v depending on the load being placed on it. I still plan to investigate it more.

One definitive test is to have it tested while in the car so you can get an amp output reading.

[Superdave]

That's the plan.. going to do that tomorrow.


*edit

I put it back in, running voltage is 14.5 and it stays running with the battery disconnected. Tomorrow i'm going to verify that the ECM is reading the voltage the same as my Fluke is...

[1988GTU]

Have you done the big 3 upgrade?

I know mine would be within (IIRC) 12.9 to 13.5 before the big three. After doing the mod it went to about 13.8/14.5... Then I went through and redid a few grounds and connector cleaning and it would not go lower than 14.0 at any time with headlights/heater/brake lights on. Then I installed the UDP, it goes down to 13.5 area, but that's it.
HTH