I have a 79 L48 that is all stock. My issue is when I start it up, the amp meter reads real low, down around the 8-9 mark. If I rev it up a could of times, the amp meter jumps up to the middle of the gauge where it should be. Do you know what would cause this. The belts are all tight, the alternator and battery are new. Once the gauge is in the normal range, it will stay there regardless of what I turn on (lights wipers...) so it the charging system appears to be normal. Apprecate the assistance.

 

Hi riley, it should be easy to check your charging system, the problem could be the gage or the alternator. Hook up a voltmeter directly to the battery, with the engine NOT running and the new battery you should see 11.5-13.0 volts D.C. The gage in the instrument cluster is a volt gage and not an amp gage like the older models had. Now turn the key to the "RUN" position, don't try to start the engine yet, we're just checking the accuracy of the gage in the cluster, at this point both the voltmeter at the battery and the gage in the cluster should read pretty close to the same. Start the engine without revving it, just turn the key and let it run at it's slowest idle and read both voltage outputs, are they still the same at a low voltage of 9.0-12.0 volts? Now rev the engine a little until you see the volt-gage in the cluster jump up to the normal 13.0 -14.5, is the voltmeter on the battery also reading higher now? My guess is the alternator field coil is not being 'excited' at the lower RPM, either you have an after-market unit that requires higher speed to excite it or if it's a stock style unit the internal regulator or brushes are at fault. Can you return it for a replacement? Run through this test and get back to us.

 

Buckshot is right about the "self-exciter." It won't charge until it spins fast enough to kick itself off.If the idle is at 500-600rpm, I see nothing wrong with having to rev it"just alittle"to kick it off.
Buckshot, I'd want more than an 11.5v reading on my battery, that's alittle low. A 12.3 or 12.5 reading would keep me from checking my charging system.
I will say that I've been back and forth with my charging system, in short, with the gauge and the light. Every once in awhile, I put the multimeter on the system. It charges at 14.2v-14.3v and the battery reads 12.2v-12.4v alone. These readings tell me that my system is operating correctly.

 

i had the same problem. look at the markings on the alt. like mine, it my say 37A. swap it out with a 63A. $37 at napa. i also replaced all the belts and fan clutch.

 

Texas Jim, I agree that 11.5 volts is on the low side for a system that's up to snuff but the point I was trying to make here was for a system that might not be fully charged given the circumstances. I didn't want to have riley overly concerned about seeing a low reading when the engine isn't running so I gave some wide lee-way, you also saw that my high was a little on the high side for the same reasons, I was only helping him find a base from which to judge the system after starting the engine. We can narrow things down a little at a time but can't get too picky on the first test. Together we can figure out the problem, thanks for your input.

 

Well I took the vette up and had it checked at Advance Auto and they said it was an aftermarket. You were right about the self exciter, they said it just needs a little more humph to get going. Found out I had a leak in the radiator and around the inlet and outlet of the alternator so I am off to the garage to change it out.

 

Buckshot, I do see your point and yes, you did go about it the right way. I had a more objective view right off the bat and yours being alittle subjective, you included the human factor, something I know that I should "be about" more often. Good going.

 

This is the first time I ever heard of a leaky alternator!

[sm=icon_cheers.gif]

 

yeah lots of things can leak in these old cars here, but if an alt leaks, well i guess you don't have to worry about cleaning up the garage floor.

 

Now come on guys!, you tellin' me you've never seen other electrical components leak? Everyone knows that all electrical items are manufactured with a prescribed amount of smoke built in. After a pre-determined time period OR if a technician (shade-tree mechanic) performs work on these items, the smoke is apt to leak out. Once all of the smoke has leaked out the electrical component has completed it's life cycle and will need to be replaced. A few items such as starter motors and alternators can be resurrected by rebuilding with new parts that contain a full charge of smoke.