Major alternator problems on 91 gp se

Ok, the 91 gp se I have keeps blowing out alternators with no rhyme or reason that I have found yet. Over the past year and a half this problem has drove me absolutely crazy. For example, 1st one went bad on a short trip to atlanta, replaced it, lasted about 3 days and went bad. Next one lasted several months and suddenly went bad. replaced it and time I started the car, it went bad. Changed that one and same exact thing happened with the next 2!! Finally the following one lasted a year and two weeks with no problems till a few days ago it went out. Now, I install another one and it lasted 24 hours and went out. Changed it out with another and time I started the car, it went bad. Put another one on and it lasted 2 days and it went bad when I cranked up the car to move it to cut grass. I have already replaced the battery with a new one, checked the positive wire from the battery to starter and up to alternator and it looks fine. I have also made sure that I charged the battery before every changeout. I am out of ideas and am in dire need of help here. Anyone care to take a stab at it? BTW, the alternator is from advance auto parts and its a palladium P79393, which has a lifetime replacement.(thank God for that!) I dont want to throw anyone off from an idea but it seems to me that they all make a slight "pop" sound right as the car is started when they go bad.

You need to inspect the wiring running to the alternator. It sounds like you have a wire touching metal somewhere and dead shorting, killing the alternator. You need to inspect all positve wires under the hood, including the wire off the back of the alternator that goes back to the battery, the positive battery cable, both from the battery to the starter, and the branch to the "charge post" near the left strut tower. The randomness of time period is what makes me think it's a bare wire touching somewhere. A few times, while replacing the alternator, you've been lucky and while moving wires around, you've moved the offending wire away from it's grounding point. Eventually, it finds its way back due to road bumps and vibration and kills the alternator.

Ok, I came home this afternoon with a better attitude about working on this thing and this is how it went....I started at the alternator, took it and the power steering pump loose, traced that wire all the way to the starter and found no problem. While at the starter I happened to notice that the silver stranded wire from the solenoid to the starter has been repaired by someone crimping on a round connector. About one third of the wire was trimmed off so it would fit in the connector I assume but it was cut short enough not to cause a short. From there I re-checked everything for tightness on the starter with everything ok there. Now I remove the air cleaner box and checked that wire all the way to the battery and didnt find any problems with it. After being frustrated not finding anything wrong with the wires I checked the connection you mentioned by the battery where the fuel pump relay is and it was loose enough to remove with my fingers. As I looked at it closer I noticed it had small burned pits in it which I guess could have been caused by the loose connection? Anyway, I smoothed it back down and shined it up with a file and put it back on tight. From there I found a loose ground from the battery to the chassis right above the top radiator hose so I shined it up and put it back on. I ran out of time so I only checked the motor ground connections to be sure they were tight and they were fine. After putting it all back together and cranking it up, I was happy to notice that first of all the alternator was working and charging at 14.3 volts and that I no longer have a problem with a slight dimming of the headlights, blower motor stays strong even when I hit the brakes.(Before today, anytime I would apply the brakes the volt meter on the dash would drop below 13 volts if I had the blower on high and you could hear the motor slow down slightly) I dont know if any of those loose connections could have caused the alternator to blow or not but so far everything seems to be much better. I guess time will tell. Thanks for the reply richtazz, youve helped me more than once here on the forum and its much appreciated. Do you think any of those loose connections could have been causing all this?

Absolutely, the loose connections were causing voltage fluctuations and were most likely frying your alternator. Electricity seeks it's own path of least resistance, so when a fitting is loose (especially the main terminal you found) it can backfeed through and cause a surge or short, resulting in a fried alternator or burnt circuit. It sounds like your issue is resolved, and it was my pleasure helping you out. Thanks for the positive feedback, we like happy endings here on AF.

richtazz, I hate to burst a happy bubble but it didnt fix it. Wife jumped in it this morning and the second time she cranked it up.....it fried it. Im not real familiar with the circuitry on cars so this may sound like an odd question but here goes. Is there anything else on this particular circuit other than the starter that could cause this? After my wife called I was wondering if there could have been a wire I missed or overlooked that may feed over to the under hood fuse box or something. If not, maybe its a flakey starter from time to time...Im really at a loss here. Im gonna hunt down the book on this car and see if it has a wiring diagram in it for the starting system. I mean, if I understand car wiring correctly, If it was a circuit shorting out AFTER a fuse it would be blowing that fuse instead of frying the alternator right? I will leave it at that until I hear back from you and go search for that book. Its around here somewhere. We will eventually figure this thing out. ;-)

ok, I just finished up tracing the wiring from the under hood fuse panel and that wire also checks out ok. When I was taking the fuse panel off and I turned it over, a small blue fuse dang near fell out of its spot, very loose. It was a 15 amp and was labled ignition. I took a tiny flat blade screwdriver and closed up the connection better so it fits tight like it should. Dont know if that could cause a spike on the alternator or not but I fixed it anyways. Im heading back out to begin removing the starter and try the one off of a 92 lumina I have in the back yard that I grab parts off of.

Well, I got the spare starter off in case you think it might be the culprit. A huge rainstorm came our way so Im gonna wait till tomorrow after work to get back at it. richtazz or anyone else who might have an idea what to try next, I'm all for it. In the mean time Im gonna go :banghead: and see if anything comes to mind. :grinyes:

You may have to pull the relay center under the hood loose and turn it over. Inspect all the wires for corrosion where they come up through the bottom. You may also need to inspect the junction where the underhood harness connects to the interior harness at the firewall. Do you have an aftermarket stereo, amp, etc... in the car?

ok, I did look uner the fuse panel and that was good but I havent checked going thru the firewall but I will shortly, and nothing aftermarket is in the car, its totally stock. If the rain lets up I will post back and tell what I found.

ok, finally quit raining and I went back at it. I found what I believe you were referring to with the large harness that goes in thru the firewall on the passenger side. It appears that maybe the belt had broken at one time and had broken the cover off of it. It was dirty and I cleaned it with compressed air and it looked good visually after I did that. Is there a way to remove it/unplug it to verify that water hasnt made its way in and caused a bad connection. I could see a large torxix screw down inside of it...is that how its removed or is it worth messing with? Im seriously beginning to wonder if it isnt just sorry rebuilt alternators. I did go ahead and put on another one this evening, drove the car for quite a while, had everything electric running, started the car several times and it never failed.....Im just at a loss.....lol......maybe it just doesnt like my wife driving it anymore:evillol:

I used to work for Advance, and their alternators/starters are decent. With as many as you've gone through, I say the problem is a short somewhere in your car. On the wiring harness, there should be a bolt in the center of the junction, and removing that bolt separates the halves. One more thing I forgot to mention. Check the wiring harness to the ECM. The ECM is mounted under the hood, beneath the plastic cover that the overflow bottle mounts to in the right front fender area. They are notorious for corroding, and the ECM controls alternator output.

Ok, I will check both of those today when I get a chance. It seems to start raining here the last few days right as I get off work. Post back later with what I find.

Well I was only able to check the computer between the rain showers and the connections were all good. I also wrote down the number just to be sure I dont have one of those faulty ones. It was a brown color, and I could only make out that it was remanufactured and the numbers were 7-7727. I already have the computer out of the lumina and it is silver and the numbers on it are 01227727 if it does ends up needing to be changed.

I have some different news on it today. My wife was driving around town and she said the needle on the battery gauge was bouncing up and down eratically for a few minutes and also the oil pressure gauge will only read 70 no matter what the RPM's are. Dont know that its related to the problem but I wanted to mention it just in case it might lead to something. So far so good on the last alternator install. Other than the wacky gauge thing today, its working fine.

It sounds like you've gone through almost 10 alternators. At what point was the battery changed?
Any chance your fan belt is slipping?

If the alternators are always going when starting then I think your idea of changing the starter is a good one.

Here's a long shot. Could a bad motor mount be letting the engine move & tug on any wires. Hey, I said it was a long shot.:grinyes:

Well, just wanted to update on the issue. So far, all of the guages are acting fine again (not sure if they are controlled by the ecm) if anyone can enlighten me on that I would appreciate it. I really have no idea what it was. It did the same thing last year in an advance autoparts parking lot. Finally, just like this time, I finally put one on and it will work fine for months. Can a bad computer or something of that nature cause this? Just curious because its weird how it happens the way it does. I will say this, as far out as it sounds, the manager at advance told me they have times where an entire new shipment of that particular brand alternator will have high failure rates, even when they test them before they give it to the customer. I dunno, maybe. Im just glad its back on the road. Thanks for helping and puttin up with me Tazz. I was at wits end for several days there.:grinyes:

Again, no problem. I'm a Stewart fan too, so I went the extra mile for ya!!!

Well, right as I was beginning to think this fiasco was over.....it blew another alternator yesterday. Well, I came home this evening and took the starter off first and found this. The stud where the alternator wire and battery wire connect to the solenoid was loose. I couldnt tell it until I got it out from under the car. The stud actually will push in and out about a half an inch but wouldnt pull all the way out. Now, I dont want to get my hopes up because everytime I do, it ends up happening again but what are the odds that could have been causing this? I went ahead and put a starter off another car I have and installed the new alternator and drove it around, started it a few times, and so far so good. If this doesnt do it, its going up for sale.:rofl:

Ok, I have changed 2 more alts since my last post and this is getting very aggravating. What in the world could it be? A parts salesmen rattled something off about check diodes but the only ones I find are built into the alt itself? Also, how can something short out enough to blow the alt out but not pop a fuse or catch on fire? Also someone said check the tensioner pulley but it seems ok, full range of motion and tight. I dunno? Anyone? Im desperate.:banghead:

fix the lumina and drive it..... sorry i have no idea whats wrong did you try to change to pcm?

Yeah, I wish it were that easy. The lumina was left in the woods for dead at a friends house for several years and rats had taken it over. I havent changed out the computer......how could that cause the problem that I'm having?....can you explain to me so I can better understand? I took some time and took ohm readings while shaking all the wires, positive and negative, no bad readings there either. I did however go ahead and took out the smaller wire between the starter and the alternator and upgraded it to a #4 and ran it straight to the battery just for the sake of doing it. I have read on some places about some systems needing a light bulb in the circuit for them to charge properly? Could that be it? I have never seen a battery light come on in the dash since Ive owned the car, just that fuel and check gauges which are on all the time. Anyways, Im sure this thread may be getting to the annoying level for some but Im just looking for help hoping somebody might see it and have a new direction for me. Thanks again.

I used to work for Advance, and their alternators/starters are decent. With as many as you've gone through, I say the problem is a short somewhere in your car. On the wiring harness, there should be a bolt in the center of the junction, and removing that bolt separates the halves. One more thing I forgot to mention. Check the wiring harness to the ECM. The ECM is mounted under the hood, beneath the plastic cover that the overflow bottle mounts to in the right front fender area. They are notorious for corroding, and the ECM controls alternator output.

To quote myself from WAY earlier in this thread, the ECM controls alternator output. If the ECM shows any signs of moisture intrusion, it could and would cause all the charging system problems you are experiencing. You've corrected a lot of issues in this car, and since it was parked and subjected to mice, there could be a bare spot in a main elecrical wire anywhere causing a dead short and blowing yet another alternator.

I checked the computer and found no visual problems with it when you wrote that. I didnt know a pcm and an ecm where one in the same. Ohh, and to clear up the confusion, the mice were in the lumina, not the grand prix. The motor blew up in the lumina several years ago and he had plans to replace it and never did so I picked it up and brought it home to part out as needed. Guess I will swap out the computer tomorrow along with the new alt and see what happens.

Ok, gotcha on the mice deal. Make sure you swap the prom from your original ECM to the other one and make sure that the service numbers are the same. A PCM is a newer version of the ECM. Pre-94 Gm vehicles used ECM's, 94-95's used a hybrid, and all OBD-II GM vehicles use a PCM. The main difference is that an ECM has a set programming that is permanentl purned into the prom. A PCM has a flash-programmable memory that can be re-calibrated for emissions updates as well as performance. The light bulb you heard about is the charging system warning light. On some vehicles, if it is burned out or missing, it interrupts the charging circuit, kind of like those cheap Christmas tree lights that all go out when one bulb burns out or is missing.

Timeout. Someone please explain to me how it was determined the ECM is the problem here?

I've reviewed this thread and find it quite an interesting read. The original poster may be looking right at his problem. It sure sounds more like a series of defective alternators or a short in the wiring centered around the output cables to the battery and starter circuits. It sounds like these alternators have quality related internal problems with either the stator, rectifier bridge (diodes) or the special integrated circuit voltage regulator.

The alternator on this model Grand Prix is a Delcotron CS-130 meaning it is a fully self contained charging system. The output is controlled by the internal voltage regulator through pulse width modulation and not by the ECM module. You can disconnect the output of the alternator feeding the ECM module and all you may get is a battery/charging system light at the IP. According to the GM wiring diagrams the L output of the alternator that goes to the ECM module is an input to the ECM only, therefore the ECM does not control the alternator output or perform any voltage regulation but simply monitors the output in order to generate the idiot light and adjust its own internal voltage supply accordingly.

I would recommended getting a known good used GM alternator or a new one. The aftermarkets leave a lot to be desired.

I've seen it mentioned on several internet forums that the PCM controls the alternator. Does anyone know what year GM PCM's started doing this? I have a Chilton's manual that covers 1988 -1993 Pontiac Bonnevilles. All I can find in this manual is that the PCM monitors the voltage & will shut itself down if the voltage is too high or low.

I've seen it mentioned on several internet forums that the PCM controls the alternator. Does anyone know what year GM PCM's started doing this? I have a Chilton's manual that covers 1988 -1993 Pontiac Bonnevilles. All I can find in this manual is that the PCM monitors the voltage & will shut itself down if the voltage is too high or low.

There is alot of disinformation on the Internet so I would not rely on that. Now late model Chryslers have PCMs that control the alternator. The info you have is correct. The best reference manual is the GM service manual and consult the theory of operation and wiring diagrams.

The operation of Delcotron CS-130/CS-130D alternators is locked in concrete and the same data I provided is part of the ASE certification exam to become an ASE certified auto tech.

The CS130 alternator can be fully bench tested out of the car and without a ECM/PCM module as part of the test fixture.

I agree that the problem most likely has nothing to do with the PCM. Since the alt's are going at start-up I'd change the starter. Maybe the solenoid is some how shorting to ground.

Ok, I hope what I found today fixed it. I had just finished up putting on the new alternator and just after I finished hooking up the battery I was installing the air cleaner box and all of a sudden I hear .......DING! DING! DING!........When i shook the car the chime went off to tell me the key was in the ignition and a door was open but guess what......the door switches had been removed before I had bought the car...so I looked up underneath the left front dash area and found that the tape had all but fallen off the female connectors and they were REALLY close to a non painted metal object that was part of the emergency brake pedal. IF this is what was burning up the alts.....it kind of makes sense....MAYBE everytime we shut the door it was causing those wires to make contact with the bare metal and short out the ignition circuit? It would also explain why the alts were burning up so intermittantly. I sure hope thats what it was so I can go back to living a normal daily life. :lol: Also, the new alt from autozone is putting out 14.8 volts compared to 13.6-13.8 from all the ones from advance. Not a major difference but happy to see it nonetheless. :)

Finally changed out the ignition switch this evening, (what a PITA that was!) but everything is back to normal and working as it should. Thanks everyone for the replies, it gave me things to look at and I appreciate it. If anyone else ever comes on here with intermittent alternator troubles, be sure they pry open the ignition switch carefully and see if its burned anywhere. Mine looked pristine on the outside but was burned and black on the inside. I cant believe it even worked in the shape it was in. Glad this headache is over.:wink:

Also, how can something short out enough to blow the alt out but not pop a fuse or catch on fire?

I'm having trouble believing that either of the last two things you found could kill the alternator. As you mentioned, a short at these locations should just blow a fuse.