My gauge will gradually go down to about 6-7 volts while driving. The lights dim and the electric fans react accordingly. If I turn off the car in this condition, I have a dead battery, and it will not start.

If I keep driving, it will suddenly begin charging again, usually around the 6-7 indicated volt range. From there, it works fine as long as I keep driving. The gauge will indicate about 14-15 volts, the lights and fans work like they are supposed to. If I turn off the car, it will start back up.

When I start it back up again, it will go through the same cycle, dropping down to about 6-7 volts before charging again. It usually takes well over an hour with a fully charged battery for it to drop down to the 6-7 volt range.

I have had my alternator tested at two different places and both said it's good.
I have a new battery. and have had it tested as well.

It almost seems like there is some kind of sensor in the alternator that tells it when to start producing current, but the sensor is out of wack and is turning on way too late.

Is there something like that in the charging system?

If so, is this condition duplicated or checked for on the standard alternator testers?

Help, it's driving me nuts, and I have to drive half way across the country in a couple weeks!!!!

 

Well, I would start by looking at all alternator wiring. Both the big red charging wire and the plug-in connector with the brown and white wires. Have someone watch the volt gauge with the engine running. Wiggle the connector and charge wire, looking for changes in the voltmeter reading. The other possibility is the charging system fuse link at the starter. Less common failure but worth investigating. G/L

 

yep, I've replaced the plug-in connector and have tried the wiggling thing.

If it were the fusible link, would that not be a permanent failure? Mine is intermittent, and somewhat predictable.

 

Then it's probably the battery.

 

If the battery was bad, it would drop dead and stay dead.....the voltage regulator is inside the alternator, which "I" think is your problem....I'd bite the bullet and put on a new alternator...worst that can happen is it doesn't fix the problem, and you just return it to the auto store and get your cash back...and as a side bar...make sure your ground connections are good...

 

Its most likely the regulator or a connection to it. Whatever the problem its intermittent, The hardest to troubleshoot. The volt Meter is telling you the story, it reads voltage coming from the alternator somewhere ubnder the dash. Next time it acts up, stop and check out the connections, its there somewhere. Or, as kb says just replace it.

 

Thanks guys, I guess I'll just replace the alternator and see what happens. Seems strange that it's tested good twice though. I have to drive it to San Antonio later this month and I sure don't want electrical problems on the way.


Thanks

 

You cold have just been unlucky and had it tested while it was in its "good" state......you did say the problem came and went. Next time it does this, shut the car off and check for a drain on the system while the ignition is off. Could be a short somewhere else that is affecting the entire electrical system. If you see a drain, pull one fuse at a time to try to isolate it. Definately not on the list of the "fun" repairs. Just my $.02.

Good luck

~Rich

 

christo,
It could be a vibration situation, heat, lots of stuff....logical way is the way you plan to do it...as I've said before....easy first, difficult later...it'll take 30 minutes or less to swap 'em and then you'll know which direction to go next, if necessary, but, if I was still a betting man, (which I'm not any more, but I digress) I'd bet the alt is the problem...
Good Luck!!

 

A power wire could be intermittenly shorting to ground. It might only touch ground after you hit a bump or something. Just a possibility, look for main power wires with cuts in the insulation or arc marks on ground surfaces.

 

Thanks for the replies. Understand that although the problem is intermittent, it is predictable. It will begin charging again when voltage drops to a certain level. Bumps, wiggles, jiggles and what not have no effect. It leads me to think it's a regulator problem, but having had it tested at two different locations on two different types of machines has me wondering.

So, a different question is.....do the alternator test machines look for and test for this?

When they are tested, do they start off the test with a high load situation (simulating a very low or dead battery and lots of amperage draw) or does it start off with a low load situation (simulating a fully charged battery and minimal amperage draw. Does the machine vary the amperage draw at all, or does it just check to see if it will generate electricity at a high draw rate?

 

i think bat power goes to teminal 1 (or 2) of the alt through the ignition switch. when this doesn't happen, bat discharges. maybe look there.

 

Have you actually checked the voltage at the alternator to see how it compares to the 6-7 volts you are seeing on your gauge?

 

Problem solved! After taking it to a third store to have it tested, the machine said it was bad. This machine was different and much more sophisticated than the other two as it does a better job of checking the regulator and (they said) varies the load on the alternator.

Could'nt find proof of purchase, so ended up just buying a new one. Slapped it in, fired her up, took her for a spin in the beautiful San Gabriel Mountains.

Dang, I'm going to miss these California canyon roads!

Thanks for all your input

 

Well then, there you have it

 

I guess that goes to show that not all alternator testing machines are created equal...