I swapped a 2001 LM7 5.3L into my El Camino and it has been just fine for the last 9300 miles. But last week wednesday I noticed that the voltage gauge dipped down to ~10V a couple times, it did the same thing thursday. On friday I was crusing and it dropped to 10V and never went back up, by the time I got home the battery was at 6V and the fuel pump just started to cut out . I figured it must be the alternator so I pulled it off put the battery on charge and took the alt to autozone to get tested. They tested it and said it was good. I brought it back home put it on started the car and it was charging at 13V like normal (13V on my factory gauge is actually about 14.5V at the battery). Today I started the car again and it was charging at 13 like normal, let it run for a minute shut it off went inside, came back out and restarted it and then it starts charging at 10V. I revved the engine up and it started charging at 13V like normal, I went for gas and it stayed at 13V. I started it after getting gas and again it was at 10V, revved it up and it went to 13V for the entire ride home. When I got home I checked the two small wires pin B was about 11.5V with the IGN on and or the car running (the battery was just under 12V at this point) and pin C was about 0.11V. I plugged the plug back into the alt and it and it was charging at 10V, revved the engine up and it started charging at 13V. I checked the voltage at the two small wires and pin B was just above 12V, pin C was still at 0.11V. I found that if I unplugged the 4 pin plug on the alt and then started the car and plugged it back in the car would charge low at about 10V, so I checked the pins again and B was at 10V, C was still at 0.11V I tried reving the car up but it did not start charging like normal, just stayed at 10V.

I doubt that the problem has to do with the conversion into my car since I kept the alt controlled by the computer and it has worked perfectly for the last 9000+ miles. I have checked the battery cables and ground connections and everything is clean and tight. There should be plenty of grounds, the battery is grounded directly to the engine, the engine is gounded to the firewall, and the battery is also grounded to the fender.

I want to say that it is the alt, but it tested good, and the problem does not alway happen under the same circumstances. The first time today that it was charging low the alternator was cold, the last time it was hot. The first 2 times it stopped charging today revving the engine made it charge, the 3rd time it stopped charging nothing I tried made it charge.

Sorry for the long post, just wanted to give as much info as possible since it seems like I am chasing an intermittent ghost

 

I took the car for a ride to the parts store today and it charged just fine on the way there at 13V like normal. But I did notice that if you looked very closely at the voltage gauge it was ticking back and forth, not much probably less than 1/2 volt. When I restarted the car after getting out of autozone it went back to charging at 10V , I popped the hood and the alt was hot to the touch.

Could the regulator be failing and it only fails when it is hot?
That was the only explanation I could think of. I think I will get it hot until it stops charging and pull the alt in the parking lot and then have it tested.

 

You didn't jack with the tiny red wire coming out of the top did you? Called the "exciter wire". It's plugged in with a weatherpack connector, easy to damage if the harness is pulled on or the alternator is dropped.

 

Not until after it stopped charging. The truck alternators are like the vette alts, they have 2 wires, brown and grey. The brown is equivalent to the red wire on f-bodies, it is the charge indicator wire. That wire is supplying approximately battery voltage to the alt so I think it is working correctly. The grey wire is labeled "Generator field duty cycle" according to the wiring diagram but I don`t know how that one is supposed to work.

 

Today I drove the car until it stopped charging, parked at autozone pulled the alt and had them check it. It tested good again . So I put it back on the car and had them do the on car test. It would work very well when it was charging and then it would just stop . So I think that it probably has something to do with getting the signal to charge. I always have 12V on the brown charge indicator wire. The grey wire for the generator field duty cycle seems to have 0.11V on it even when it is not charging. Based on a post in the C&H forum about alternator wiring on a vette alt I believe that the grey wire should have IGN + 12V and the brown wire should have 12V going through 500ohm resistor and the alt will work. Can anyone confirm that?

 

Im having the same problem, except on my 2001 F-Body. It will start and charge fine, but drive it for awhile and the exact same problems you describe will happen.

I think one is heat, I think another problem with mine is moisture. I tried to fire it up this morning when dew was all over everything, and it didn't want to start. I think I will go ahread and replace the factory battery cables, and try to go from there.

 

Its your alternator. I just went through this 2 weeks ago.

Alt would chatge fine when cold, but when the car got up to temp, the alt would start to quit charging.

 

Mine does this too...On start up I am at 10v...jumps up to 13v or so after a few seconds...then backs down to 10v when you turn on the A/C...then back up to 13v after a few seconds...then clicks back/forth when I hit the turn signal. Not as bad a problem as total loss of output from my alternator over time like you though...replace it with an A/C Delco part, IF ANYTHING don't buy anything without a lifetime warranty!

 

Damnit, if it's not one thing, its another.

Would this also cause my starting problems?

 

Yes, if the alternator is not charging your battery will be drained and if it is drained enough your car will not start.

 

I don`t think it is my alternator I checked the battery, charge indicator, and field voltages today as I took it for a ride. The alternator was charging and the battery was consistently at 14.4V , the charge indicator wire stayed around 11.3-11.8V and the field voltage was around 2-5V. It charged just fine for about a half hour, then I couldn`t stand it anymore, I noticed that before it would charge ok until you stopped and shut the car off then it would not charge. So that is what I did, when I restarted the car the battery voltage dropped to 12v, the charge indicator wire went to 2.5-3V and the field voltage went to 0.03V for the rest of the ride. Now I am thinking it must be a computer problem since the computer supplies the voltage to the charge indicator wire and the field wire.

 

im having the same fing problems! put new alt in and now i have no charge wtf?!

 

If you have an f-body check the single red wire in the four pin connector. From what I hear it is very small and easy to break while replacing the alt. It should have ~12V on it while the car is running.

 

I'm having this same similar problem. I checked the red wire and it looks okay but it did get tugged on when I replaced the alternator a week ago. How do you go about replacing it?

 

Hey guys. Heres a little update on my situation. I went ahead and changed out the three main positive leads from the battery, with a new AC Delco harness to the starter, alternator, and fuse box. The wire leading to the alternator was fried, is was frayed and bent and had alot of dirt on it. I changed it out, and now I don;t have a problem with it starting.

However, the alternator was still surging. When it was off the car I took it to AutoZone, and it tested good. However, when I reinstalled the same one, it surged and I took it to autozone where it tested negative.

I went ahead and reinstalled a new autozone unit, but unfortunetly I am still having the same problem, except not as bad. The car will charged fine when the RPMS are up, but when it idles it tends to dip.

I believe the alternator is a 102 AMP, but Im thinking it just might be way to damn hot for the Autozone unit. Im seriously going to looking into a nice aftermarket unit, since its a constant hassle changing it out.