I have installed 3 brand new alternators with less than 100 miles total on all three. When first installed I would run a/c, lights, defrost...alternator charges fine at idle and during daily driving. Everytime I have gotten on the gas and hit 5,000 RPM the alternator quits charging and quits working. I pull the alternator and take it to Auto Zone to get checked and they can only get it to put out 11volts.....I am totally lost at what to look for...please help

 

quit going above 5000 rpm?

 

are you buying ebay alternators?

 

use a underdrive pully set up.

 

There could be something wrong with the alignment, maybe not bad at low RPM, but at that 5K mark it's bad enough to mess the alt up. Just an idea. I don't know of any wiring or electrical problems that would cause that.

 

the alternators are brand new delco's........I know I have some sort of electrical problem but don't know where to look.......I have the 5.7.....I thought it was the the power steering pump leaking onto the alteranator, but I replaced it.......What could cause an electrical problem that would kill an alternator at 5,000RPM??????The car is all stock......and I don't know where to look.......I have to have some sort of electrical short,,,,,,just don't know where to look.....

 

how old is the belt? maybe its the idler pulley? Under normal driving conditions you shouldn't be above 5 grand enough to worry the alternator not working. Maybe when you go that fast the car just draws extra voltage and your volt gauge drops. As long as it doesn't draw your battery down under 12 and your car starts fine everyday, I don't think you have a big problem

 

what yr is the car? do u have a amp? what add ons do u have? check all your connections, ground and hot.

 

You may want to get a cheap slide on ammeter ($15) and place it around the alternator output cable. Turn all electrical stuff on and see how many amps are drawn at 5000 RPM. The alternator is rated at 120/140 AMP, depending on car model. If the load causes the draw to go above the rated output, it can overload a rectifier diode and cause it to blow, which would cause the low voltage you mentioned. Also make sure all wires to the alternator are properly connected, especially the sensing lead which controls the alternator output.

 

I replaced belt after first alt quit, no it's not that the alternator just quits at high R's....When I hit 4000 R's the alt, quits and will not work again. I have removed all after failure and taken them to Auto Parts store and they confirm same readings as I got in my car, Once car got to above 4500 Rpm, alt will not put out more than 11 volts at any engine speed......my car is 2001 z-28 with the 5.7 with everything stock, including the radio........