Hi again folks, need some quick advice. With my engine running , engine fan on lights on blower motor on all internal electronics on, the alternator reading on my dash bounces around from 11.7 turning on the dummy light and then up to 13.8 and 14 volts when warm. When cold its solid at 14 or 13.8 volts. All accessories are on the same as before. Engine fan is on all the time, I rigged that myself. So is my Alt going south? It is still charging but it seems to be turning on and off dimming the lights and brightening the lights. Regulator in the alternator? My auto parts wont replace it unless when they test it, its not working at all. Lifetime alt. But i know these cars and you cannot go far on battery juice without that alt. Its probably going bad but maybe theres somethin im missing. Thanks in advance corvette geniuses.
P.S. does that helms manual tell you where the part is also? I was helped out here with a page of instructions and it looked like it came from a manual. It described sensors and relays and exactly where to find them. Near this behind that across from that. Ingenious. I gotta get me one of those. Thanx

 

When you have a heavy electrical load, the alternator cannot deliver its rated current at engine idle speed and the voltage regulator can make the alternator output vary under these conditions. If the voltage comes up and stays around 14 volts, engine cold, when you race the engine slightly, then you have a normal alternator and electrical system. Engine hot, the alternator output will drop to about 13.3 volts.
When driving you don't sit for long periods and your alternator will charge the battery back up when you get underway. If you are in the habit of having a heavy electrical load with the engine idling for long periods, I would recommend a small spacer under the throttle stop to raise the engine idle speed to save your battery.

 

When warm the vehicle charging tends to jump around even at a consistent cruise idle but only when warm and itermittently. When cornering, I believe it even affects my engine spark. It does drop dangerously below 11.5 at times. So far it hasnt left me stranded. I guess ill just wait till it quits. Thats what AAA is for anyway. Thanx JFB for your ingenious imput.

 

It effects injector pulse width - though this is oversimplified, injectors are held open longer with lower voltages and though the ECM can keep it running down to about 9 volts, most injected motors don't run very well below 12 volts and most do much better at 13 (someone around here captured a bunch of data once just to prove this point).

It shouldn't be bouncing around during above idle operation nor is running the fan full time any good for it. If you have cooling system problems, fix them so that the fan can cycle which will save some amps for everything else that's running as well as the battery. That's how all electric fan cooling systems have worked for the last 20 years or so - why does yours need to be different - was the Vette designed wrong? Otherwise, upgrade for more output (difficult since most put out the same 35, maybe 40 amps at hot idle).

Since it's difficult to find a single item that might be drawing it down at cruise, I'd try some simple stuff first and turn off the stuff that draws the most juice - fan, a/c and lights. If there's any significant difference in any of those items, investigate further. Otherwise replace the alternator.

 

and or battery...

 

Thanx for the input SunCr. Ive been running this vehicle, fan on continuously, for over 5 years and no troubles. I still think that my Alt is going out. As for the vehicle built right, vehicle idling at 230 degrees before the fan turns on, I think that is crazy, especially when many electronics under the hood are vulnerable to heat. Now if they were vaccum tube switches instead of transistors, i would agree. Thank goodness the ECM is in a air conditioned environment. Example: alot of relay connector wires in mid eightys vettes melt back and fail due to excess heat. The only thing a 230 degree idle is for is to lean the car out and pass smog other than that, heat kills.

 

Mine jumps around a little also. I have a new alternator from Autozone (gold w/ lifetime warranty) which is 1 year old. The only odd thing I see is when my turn signals are on, I can watch the volt meter go up and down as the turn signal goes on and off. It also causes the backlighting on the speedo to flucuate at the same rate. As fans come on and off, or the heat on, the volt meter does move, but everything seems to be charging and running correctly.
I don't remember if the turn signals caused that before I replaced the alernator or not.....the battery is relatively new, less than 2 years and fully charged.

 

Slapshot, could be your alt is going south. I ended up taking mine in to kragen to have it checked, even though I knew it would pass. It passed, and the machine said that it was charging but the technician said that the voltage was on the low side. I told him when it warmed up, it would start turning on and off. He spun it manually and said that it sounded like it was failing. Of course It is fine when cold but after it heated up it would start flickering so he tested it a couple more times and still passed. He gave me a break and said that he would sell a upgraded Alt for the difference in part numbers, which was fifteen dollars. Well I didnt feel like putting the alt back on and driving around until it got hot for him to test again so I payed the fifteen dollars. Just seems wrong when they promised a new lifetime alternator back in 1995 . But Didnt want to hassle. So I put the new alt back on and charges fine now, even after a couple of hours on the road. Those lifetimes have to fail in order to get a new one which sucks but our batteries cant get us two blocks with all those electronics on the car after the alt fails. I still want to write Kragen on that. A liftime alt is a lifetime alt...hmm... I think ill do that right now..haha..Keep vettin..

 

The only transitors I can think of in the engine compartment (up until '89 at least) would be the Blower Control Module (cooled by the a/c air with it's heat sink positioned next to the Evaporator outlet). For the later Years, the ECM seems to have a remarkably better record than those that have them under the Dash. In fact, I don't know of any domestic or foreign vehicle recalled due to ECM failures (and the Federal Emissions Warranty for the ECM is what - 8 years these days?). Ford, of course, had some ignition module problems which resulted in some clever litigation, but if I remember correctly, that was due to poor insulation (and it didn't seem to matter if the engine was hot or cold). You also seem to think that there is some direct correlation between coolant temp and the air blowing around the engine compartment. Seriously doubt that it's so simple, but what the hell.

More often than not, a melted wire is indicative of a voltage drop or high resistance, not latent heat from the engine compartment. The harness connectors are crimped not soldered. Add a little resistance, a weak connection, and a high draw device - like a fan or a blower motor - and the harness will melt in two - particulary those that are allready near max thickness or gage for the typical amperage of the driven device. The first step is to take apart the weatherpak and solder the connectors. Inspect the insulation closely. There have been multiple posts about it shrinking and pulling away from the wire (and it's debatable as to whether the cause is heat - that insulation supposedly spec'd out at 600 degrees - or exposure to whatever might be floating around in the air), but once that happens, the copper strands will deterioate with a resulting increase in resistance (to say nothing of the potential for a short to ground) with a resulting increase in heat. Increased resistance in the wiring of any of the devices the ECM relies upon to control fuel delivery can cause a host of driveability issues, (though the ECM does have some wiggle room because it monitors system voltage). If my dash was blinking, I'd be more inclined to look at its ground - or the ground or the wiring of the device being operated when it was blinking, particularly if it were the turn signals or lights (at which point I'd also clean the sockets and smear the insides with a bunch of dielectric).

The cooling system of our Vettes was designed to turn on the fan and keep it below 230 degrees. Always best to compare the gage with the Engine Coolant Temp Sensor, but if you've done that and the fan is coming on within design parameters, then you might want to make sure that the fan is getting all the juice it needs to run at full speed. If it's melting wires, that's a good sign that it isn't. If the dash gage shows less than battery voltage, it isn't. If the wires and everything else are good, then the radiator or some other component isn't. I mean come on - it left the factory functioning right - why isn't it that way now?

I do agree that heat destroys the Alternator - it sits too damn close to the header and the hood is snug up against it to boot. Chevy was certainly aware of it (well Vette Magazine was - they were allready telling everyone to carry a spare when I bought mine new). My first one was shot within 6 months and I quit counting after a dozen - at least GM paid for the first 3 or 4.

 

The strange thing is, it did it since this alt was new. Not that buying a bad one is out of the question either. I have heard of people who went through several "new" ones to finally get one that works.

Next time I'm under the hood, I'll **** it off and swap it out...life time warranty