For last few months my TBI motor ran very bad. Under a load it would hesitate and feel like not all the cylinders were firing and just generally fall on it's face throughout certain RPM ranges and feel as though it had a misfire issue. At certain RPM's it also felt as though 1/4 of it's power just dissapeared. The car would also have idling issues when the fan came on, it would start stumbling and the exhaust sound would dramatically change. I was at the point of having a new chip burned for the car thinking this was the issue.

Three days ago the alternator went bad. I replaced it with a new 104 amp alternator and since the car doesn't do any of this anymore.

When the old alternator finally went bad it was spitting paper like stuff out the front and was extremly hot. where the cases split apart had like some glue like stuff dripping out and the rear bearing was gone. Prior to it doing this it never showed a charging problem. It did however from the time I did the conversion have a loud whinning sound. It was always above 13 volts but the starter always seemed to turn the motor over slower then I thought it should.

 

My car was doing the same thing, then I replaced the alternator. Good as new! A week later, started doing the same thing. Could the new alternator die that quickly?

 

could happen

 

When an alternator rectifier diode opens (quits passing current at all) you loose about 33% of its capacity across the board. Since the regulator attempts to keep up anyway, it increases the current to the field winding to accommodate. The more current to the field winding, the louder the whine, more heat, more load.

Now here is the cool part, when a rectifier diode bridges (passes current in both directions) you still loose 33% of capacity BUT the alternator is now hitting your strictly DC system with up to 20 volts of AC current. Since almost all the triggers in the computer and electronics use AC triggers, this "noise" can really freak the system out.

To test for a bridged diode, put your DVOM on AC 12V scale and test between alternator case and output terminal, if you get significant AC signal there, you should investigate your rectifier.

The most frequent diode failure is an open, then second probably a short; I have only seen a few bridged diodes and they caused major issues, some intermittent.

 

I'm with Texas on this one. The diodes (I beleive there are 3 in parallel) are very important little things to the proper functioning of your alternator.

Alternators are, by their nature, AC devices. Just look at the name: ALTERNATOR. As in back-and-forth: AC current. The diodes are like little electronic one-way doors that only allow current to pass through them in one direction, turning the output into DC current. If you "bridge" or short-out one of them it allows AC voltage to leak into your car's DC power system. There aren't enough filters in the world to keep that from affecting your cars ECM and all the sensors it must read and drive accurately- all designed for DC voltage. It freaks out, basically, like you would if you woke up tomorrow and half your furniture was on the ceiling.

I will say that I've seen quite a few alternators with shorted (bridged) diodes. Well, enough of them anyway over the years to be mindful of it- maybe 6 of them out of about 50-60 dead alternators. When diagnosing "odd" engine behavior an alternator check is one of the first things I do, along with checking all grounds.

Oh, and don't rely on your voltage gague to tell you when this has happened. An A/C voltage leak won't necessarily cause the gague to read much differently (and how could you tell anyway with the notoriously inaccurate gagues GM put in 3rd gen f-bodies?).

 

did this happen to a crossfire system. i think im haveing the same problem with no explenation and alot of money wasted. hesitates between cold and warm with very light hes. between cold and warm

 

No this isn't a crossfire car ..... it has 1990 TBI stuff

 

I saw it once where the gauge was a blur with the engine running. The rectifier mustve been pretty shot for the gauge to do that.