Voltage drops/ lights dim on WOT--- Alt tests fine

[MBC Racing]

I have a problem that is plagueing me.....

My alternator failed on me... was a delco rebuild and high rpm resulted in a wire coming off the rotor. Took it to a shop that rebuilds alts and starters and they rebuild it. I put it in the car and it works fine. HOWEVER.....

When driving normal, it works fine.
At WOT when COLD, it works fine.
At WOT when HOT, I can watch the lights dim and the voltage gage in the car drop down.

I tried to determine if it is a bad wire going from the PCM to the Alt. Spliced in a new wire from the pcm to plug.... same problem.

I also tried to see if it is rpm or WOT related.... When hot, above 4500 rpm, I can see the lights dim and voltage drop. I put the car in 2nd and slowly rolled into it to 6000 rpm to test.

took alt back out and broght to the shop. they replaced rear cover, brushes, regulator, diods..... it is all new now. They got it good and hot and ran up to 10k on their machine. Works perfectly and put out 130 amps. Put back in car and it does the same thing.

Can anyone tell me if there is something in the PCM that would cause it to do this? anything I could data log to look to see what is commanded?

Not sure if this is messing with anything else such as fuel supply or what not since the voltage is dropping. It would appear to be a PCM issue telling the ALT to cut off??? Not sure why it would do that. Kind of like how the AC shuts down at high RPM or WOT......

I am getting tired of pulling this thing out of the car.

One other note is that I have a Racetronix pump and wire harness that is fed directly from the back of the Alt. Shouldn't matter since the alt is directly connected to the battery that is 4' away.

Car is also a M6 to A4 conversion. I swapped complete engine/trans harness. Doubt its a problem, but worth mentioning.

I don't recall if it did this before the atl stopped working.. Never really drove the car at night to notice

Any help is appreciated. thank you!

[MikeGyver]

I had the same problem, a new Bosch alternator, not a rebuild, solved it. I understand that the brush springs available to the rebuilders bounce at high rpm, effectively shutting the alternator off. At 5000 rpm on my truck, and this is just a guess, the alternator is at 18,750 rpm. That guess is based on the crank pulley being 7-1/2 inches, and the alternator pulley being 2 inches. I don't feel like getting off the couch and measuring, so it is a guess. Get a new alternator.

[Nitroused383]

Look for a used OEM AD244 DELPHI 145 amp truck alternator at a junk yard. They are great alternators, much better than the stock cs130d junk.

Good info http://ls1tech.com/forums/generation...-failures.html

http://www.youtube.com/watch?v=aOPcnX7V7i4

[MBC Racing]

Thanks for the info. I read up on LS1tech about the alt swap to the truck alt. The rebuild shop has been more than willing to work with me and is actually frustrated about this issue and wants to solve the problem. I am going to pull the alt from my other camaro and see if the problem goes away. If so, the shop said they will build a complete new one for me and see what happens. I could do the truck alt swap, but there really shouldn't be any reason why the one I have shouldn't work correctly. Especially if the alt i take from my other car fixes the problem. Appearantly there is nothing in the tune that can be causing this issue????

thanks

[MBC Racing]

I had the same problem, a new Bosch alternator, not a rebuild, solved it. I understand that the brush springs available to the rebuilders bounce at high rpm, effectively shutting the alternator off. At 5000 rpm on my truck, and this is just a guess, the alternator is at 18,750 rpm. That guess is based on the crank pulley being 7-1/2 inches, and the alternator pulley being 2 inches. I don't feel like getting off the couch and measuring, so it is a guess. Get a new alternator.

I will see what happens when I do the swap with the alt from my other camaro. should be interesting....... Rebuild shop said they will keep at it until mine works once we can identify that it is 100% alt issue and not some other car related issue.