I have an 85 coupe.First, just let me say that I'm a mechanic specializing in electrical and aside from replacing the ecm I've checked about everything possible, but, you never know, nobody knows everything and someone out there might have a simple answer to this problem that I overlooked. I've had this problem since I bought the car and I just learned to live with it but I really would like to straighten it out. The voltmeter rises and falls with rpms. When I install a new alternator it stops it for a little while but always returns. Besides myself, I've taken it to 2 automotive electrical shops and they can't find it. I replaced the alternator 4 times using 2 different amp models.I changed the batteries twice, the starter once, regrounded the engine in 3 spots. Checked for and found no draws on the electrical system. When I first replace alternators , the voltmeter would work normally but after a while the dash lights would flicker slightly ,then the voltmeter would start acting up and as soon as the car would warm up the meter would go down to 10 volts at ldle and 13.5 on acceleration. Eventually the voltage regulator would burn out. this went on up until I replaced the 3rd alternator and they stopped blowing as fast and this last one has lasted the longest, about 3 yrs. :confused:

 

Find a new auto parts store. Do you have underdrive pulleys, huge stereo amps, or multiple cooling fans?

 

I wish it was as simple as changing auto parts stores. This isn't an easy one and as you can see, out of 33 people that read this post, you're the only one that came up with an idea. Actually, you're the only one to reply period. To answer your question; i don't have any of them in my car, it's bone stock. It looks like I'm going to be stuck with this problem for a long time. :chevy

 

I've read your initial post several times, trying to help figure this out. At the end you said they quit burning out so fast. What quit burning out so fast? The alternators?
Over what period of time did you replace the alternators? Have you checked the volt meter guage for accuracy? I own a 96 so I don't know where the voltage is read from on your car, which I assume is an 85. Where does the voltage meter read the voltage from? When the guage starts going up and down like a tach, is that the guage in the dash? Does it do the same at the battery?
I'm sorry for so many questions but trying to diagnose without all the information is almost impossible, because you may have checked everything I am thinking about and this will just save time.

 

O.K. CowboyNVette, Here goes.. What wasn't burning out as much was the voltage regulator in the alternator. This went on over a period of about two and a half years.The volt gauge in the dash is 1 volt lower than actual battery voltage, but, in it's own right it is accurate, like I said before, when I put a new alternator in the gauge would read fine until the regulator would start to go. I checked it with a voltage meter both when it was working good with a new alternator and when the regulator started to go and the dash gauge was accurate. Yes, the gauge in the dash and the battery both act like a tach. The voltage coming from the alternator somehow gets corrupted and rises and falls no matter where you put a tester. The bottom line is even though I'm not blowing alternators anymore, or as much, something is affecting every alternator I put in and eventually destroys the regulator, but not before acting like a tach for about a year. Well, that oughta keep you busy for a while. Let me know when you want more information. You can ask me as many questions as you like, after all, thats the whole purpose of this forum right?, to help each other if can. Later Dude :chevy :cheers:

 

I have the exact same problem with my IROC. I haven't even begun to try and locate this problem yet. Hopefully this thread will geve me the answer too.


Robert

 

Does the '85 have the SI or the CS alt? There used to be a website for SI repair, but I've forgotten where it is - you might try a google search.

If it's CS there is a good repair/troubleshoot manual here - http://www.alternatorparts.com/cs130_sbpage1.htm

The CS units use a PWM voltage reg. If the regs are failing in service it is (like most electrical parts) probably because of heat. I was having alt failures on a CS 130, and eventually solved it by stepping up to a CS 144 rated @ 140 or 150 amps - I forget. That one has been running for 4 years or so without problems. The extra thermal capacity seems to help.

 

The voltage regulator gets its power from the ignition switch and if the ignition switch contacts have resistance, then the voltage regulator will not get the current it needs to control the alternator field current and in this condition it will provide constant inadequite current and your alternator output voltage will be directly proportional to the shaft speed. The symptom of your dash voltmeter reading 1 volt low tells me that you have a defective ignition switch because the normal voltage drop across the ignition switch contacts is about 0.3 volts, your 1 volt drop is proof. The dash voltmeter reads the voltage on the switched side of the ignition switch contacts. Replace your ignition switch and your alternator problems will go away. Actually there was never anything wrong with any of your alternators, they were doing what they were supposed to do. They just were starved for field current.

The ignition switch gets current through a fusible link on the jump start bolt next to the battery (there are 8 fusible links there). You might have a good ign sw , but a poor connection (loose nut on the jump bolt), or a fatigued fusible link with moderate instead of low resistance. With the car running, measure the voltage drop across the fusible link to the ign sw and across the ign sw contacts. One or both are at fault.


[Modified by jfb, 11:47 PM 12/5/2002]

 

Jfb, I applaud your answer , it being technically the best I've heard so far but, The ignition was changed a year ago and ALL the cables and heavy gauge wires including fusible links were changed along with every relay, fuse, plug connectors ect... Like I said in my original thread, I replaced just about everything except the ECM. All the alternators I went through were not good either. Every one had a fried regulator whether it took a month or a year. I have to lean towards the reply sent in by KAISER who stated that most likely excessive heat in the engine compartment is causing it. I'm using an aftermarket steel and copper radiator that makes the car run hotter than it should especially when the air is on and up until right now it never even dawned on me that the excessive heat it's creating is probably raising the temperature of the engine compartment dramatically. I gotta look into that . thanks for the input. :chevy

 

I agree that engine compartment temperature can shorten the life of your alternator and the voltage regulator, BUT, that won't explain your 1 volt drop to your voltmeter. I would still measure the voltage drop from the battery positive terminal to the jumper terminal and then to the input and output side of the ignition switch. There should not be 1 volt drop!

 

Well, maybe that's all good info - I don't have a wiring diagram for an '85 & I haven't seen an SI alt in years - that's a pretty old design.

But looking at the schematic for the CS 130 (fig 3 in the site previously given), there seems to be a resistance built into the L or I connection between the alt & the ignition switch - I thought SI's were the same. The ignition switch L lead (I thought) just forward biased the rectifier diodes for start up, and I was under the impression that line required a resistance to work. Maybe I'm mistaken - or perhaps the schematic is wrong.

Anyway, if it really has an SI you can figure out if all the connections are clean and tight.

The CS alts are smaller, lighter, and produce more current - if you want to step up to the newer design there is a site here that looks at the conversion - http://www.novaresource.org/alternator.htm

 

Here's what seems to have fixed those symptoms in my '86. After I installed a new alternator, I noticed the dash lights starting to flicker again slightly. Fortunately, while doing the alternator, I noticed corrosion under the battery tray. Out came the battery and tray - the corrosion was terrible! Cleaned the engine ground strap connection, the battery ground (same connection), frame, and, hopefully, the brake lines that I could hardly see. New tray, new battery, and no more flickering or wild voltmeter fluctuations. Good luck.

Ray


[Modified by StarShipCmdr, 9:56 PM 12/6/2002]

 

First let me say thanks to everyone that responded to this thread. It's good to know there are competent people willing to help others with their problems. As far as the battery box goes, mine is clean and still painted. As I stated in my original thread, I regrounded the engine and even directly to the alternator with 3 new grounds besides the stock ones. Guys, this is a tough one. Like I said before, I am an automotive electrical tech and this is the only electrical problem that I haven't been able to solve. Being that it's my own car makes it a personal disappointment. I can fix other peoples vehicles but I can't fix my own.lol :nopity

 

Kaiser, I have a 120amp SI alternator in the car . :chevy

 

Well, if all the wiring checks out then it may be a heat problem.

I think you will find an aluminum radiator runs with a lower temperature approach on the air side (better heat transfer coefficient), especially if you use dual fans. I thought GM stock AL rads were less than $200 - it might make more sense to bring that up to spec, rather than keep buying alts. Plus you will lose some weight on the front.

The SI's are like a 30-year old design. Unless you love antiques for some reason of your own, why not try a better unit? The 'modern' CS is only a 15-year old design.

good luck

 

Back to the drawing board!Well, it's definitely not heat. I put a brand new alternator on today and left the car running for 5 hours in my shop with the hood open and a fan blowing on the engine. For the first 2 hours everything was ok but then all of a sudden it started taching just like all the rest. This is bull s.h.i.t. On the CS conversion, does it come with it's own pulley or do you use the serp pulley from your SI? Will the pulley from theSI even fit on the CS shaft? Then there's a question of belts. Anyone know these combinations for an early C-4 before I take a sledge hammer to the electrical system?lol :smash: