I have a 99 FRC 6 speed. Recently I have been having voltage issues while driving. The volts would constantly jump around between 11.5 and 14.5. The car then sat for 6 weeks and I had to jump the car to start it. when I went to go start the car the next day I couldn't even jump it, so I had the battery tested and was bad, so I replaced it. The car started fine now but the voltage would jump around. Starting at 14.1 it would slowly drop, I had it down to 13.1 after about 10 min of driving so I figured the volt regulator was bad and it wasn't charging well. I bought an alternator from rock auto (this one) http://www.rockauto.com/catalog/more...nid=492&jpid=0
but now the voltage is more stable but wont go above 13.8 and the "charging system fault" code keeps popping up. Here is the picture of my old alternator, I know a lot of people order the wrong one, and I'm not sure if I did. Any help is appreciated, thanks

 

I recently had a similar problem, while driving the voltage would move from low 14's to 11.8 - 11.9 - 12.9 - then back again. Obviously at the 11.* range the alternator wasn't charging. The percentage of time the alternator was charging was dropping fairly fast.

I pulled the alternator and took it to a local alternator / starter shop. They tested it and confirmed it was toast - they said the diodes in were shot. They also told me to get a new one - that their cost to rebuild was going to be more than a new one ???

After spending more than a little time on this forum - and even more time searching various Internet sites - and checking ground connections and testing continuity of some wires, it seems that I had a bad alternator. So - found that there are two part numbers for the alternators used in the 2002's - my old alternator (P/N 10246534) had been discontinued - the new part number is 10316782. I bought mine from a GM Dealer that sells via the Internet. Bolted it in and it worked perfectly - but - it was NOT cheap (as in a bit over $400 plus shipping). I bought from a GM dealer because there were quite a number of posts here on the C5 Tech forum where rebuilt alternators through the big box auto stores did not work correctly - to be honest there were also a number of posts that they had rebuilt alternators that did work correctly. But in my case - the new GM alternator did fix the problem.

So - in answer to your question - it's entirely possible that your replacement alternator is the problem... Please double check all part numbers for your particular application before dropping any hard cash, but if you do some searching - it appears that the C5 alternators can be rather finicky.

Also thanks to Bill Curlee who's posts on the C5 electrical system had a tremendous amount of very helpful info !!!!

 

I sure wish you guys would do a little research on this forum before any work on your car,these vettes are not like the old days ,you just can't start changing parts and jumping the C 5 is a NO NO !!!!!

 

So I installed the old alternator back into the car and the "charge system fault" is gone. Then I unhooked the positive battery cable while the car was running and it didn't shut off. The issue is the volts start at 14.1 when the car starts then jump around from 13.2-14

 

Why did you do that??????????????


Mr. Sam

 

If your alternator's voltage regulator is bad, why don't you just replace the regulator, instead of the whole alternator, to avoid having to deal with those charge system faults? It is also less expensive. Check this post for more info on replacing the regulator (both, 97-01 and 02-04, are around $30).

Don't disconnect the battery with the engine running! The battery acts as a capacitor to "smooth" out the alternator's "wavy" output and filters surges/spikes. Check this post for more details.

 

my friend said if the car kept running the alternator was charging.

 

the most volts I've seen is 14.1 but usually sits at 13.5-13.8 wouldn't that also indicate the alt isn't charging all the way?

 

IMHO - I wouldn't take a whole lot of automotive advice from your friend. While what he is saying is technically correct - it's also correct to say that one way to tell a gun is loaded is to put the barrel to your forehead and pull the trigger... That technique your friend recommended would probably be fine for a 1970's vintage car that didn't have any transistors in it except for the radio - but today - if the voltage went high when you disconnected the battery, that could have trashed several rather expensive computers in the car.

The fact is that anytime the car's voltage while running is higher than the battery voltage when the car is turned off - the alternator is functioning - at least at that one instant in time. You had seen lower voltage on occasion - so it's safe to say the for one reason or another at those times the alternator was not charging. The reason for the no charge condition is the issue - it could be a bad ground, it could be a high resistance connection on pretty much any part of the charging circuit, or it could be the alternator.

As akapounder pointed out - these C5's are electrically very complicated - you can do damage pretty easily, so be careful.

As for why I didn't just replace the regulator in mine - I kind of figured that if the Alternator / Starter specialists thought it was cheaper to replace than rebuild (my alternator was a very low mile OEM unit - and the bearings seemed to be in perfect condition), that was probably pretty good advice. I had taken a look at the time and didn't see any replacement regulators - I've since found one place that may have a replacement regulator - but the way the site reads - I'm not sure if the rectifying diodes are included or not, and since my new alternator seems to be working just fine - rebuilding the old one "just in case" isn't really a very high priority.

 

So you think best thing to do would check all grounds and then if I have the same problem replace the voltage regulator? Drove it today. was at 14.1 on first start after 10 min of driving its sat around 13.3-13.8 fell under 13 only a few times when idle was low.

 

Disconnect Battery and fully charge. Do not Jump start! If you do, very good chance will kill EBCM.

 

How are you measuring voltage? With a multimeter directly at the battery posts, or going by what the DIC says?

You have to measure directly at the battery and also check what you have directly at the alternator. The readings should be the same or very close.

The DIC reading is from a point after the ignition switch, so it is affected by how "healthy" the ignition switch's contacts are.

 

Like was previously stated,,, This isn't your grand dads 1970 Buick. The charging circuit is a LOT more complicated and cant be treated like cars of past.

Here is the charging circuit:



1. The RED (13) wire is the BATT wire. That wire is connected to the battery THROUGH the bolt on the starter SOLENOID main power input terminal. IF,,,,,,,, that solenoid terminal is LOOSE/CORRODED/BROKEN/BURNT,,, you will have **** poor fluctuating or NO charging voltages

2. The RED (1) wire connected to the connector on TOP of the alternator (PIN "D") is the feed back wire that samples the cars battery voltage and tells the REGULATOR what the voltage is so it can adjust.

3. What do you THINK the charging voltage should be??? There is NO set value. Sometimes it can be at 13.8 and sometimes it can be at 14.5. It all depends on what the regulator and PCM determines what it needs to be.

YES,,,,,,,,,,,,,,, THE ONLY WAY to absolutely know what the battery charging voltage is would be to measure it directly on the battery terminals. The DIC voltmeter and IPC Gage does NOT actually tell you what battery terminal voltage is:




IF, you pull Instrument Panel Fuse box FUSE# 19 , the DIC and IPC voltmeter will NOT register. The feed comes from the "HOT in RUN AND START (ignition switch fed buss) If the contacts in your ignition switch are corroded/burnt/carbon coated, the switch output will be something LESS that battery voltage.

BC

 

I am confused (not hard at my age). The owners manual gives specific instructions on jump starting my '04 if needed.

 

Bill Curlee:
Those that think their indicated voltage should be a certain constant number (or in a very very narrow range of numbers), might need to stop overthinking things.

 

Don't be confused. You can jump start your C5 just like most any other car/truck. Just observe the normal safety precautions and you'll be just fine.

 

OP:
This particular unit looks to be the correct choice for you UNLESS you go and have your old unit rebuilt.

http://www.rockauto.com/catalog/more...nid=492&jpid=1

 

and Your alternator may be fine after all. Don't return it as core!!!

As previously stated, you have to measure voltage directly at the battery and also check what you have directly at the alternator. The readings should be the same or very close, otherwise it may be what Bill just mentioned in point #1.

 

Wouldn't be the first time an unintentional misdiagnosis has occurred.

 

So I installed the old alt back and all was fine for a week. It rained pretty good here lastnight and I went to go start the car this morning and got one click and nothing. Lights and radio work just fine.