I've noticed over the past few days that my volt meter keeps jumping around and this morning it's just starting to slide low, right now hovering around 12.

Tonight I"m going to take it to Kragen and have the batt and alternator tested. I just bought the car and it could be that the batt is bad b/c it was rarely driven by a little old lady. It's an 86 S4 and after doing quite a bit of research it's my understanding that th alt pretty much is weak at only 60amps, right? So upgrading it to an S5 alt should be the best thing. I don't think an FD alt is justified in my vehicle as I'm not running an amp and it's an N/A.

Now, where do I find a replacement alt? Take it to Mazda or will I find a replacement at Kragen? I'm new to the RX and I do not have a garage to work in so my options are limited.

I'm in San Diego so any advice is helpfull.
thanks
e

 

If you change you mind, than details could be found here on the FD Alternator. https://www.rx7club.com/forum/showth...5&pagenumber=3 Eitherwise, a s5 Alternator Is a significant Improvement over the s4 one.

 

Also, please remember that it is highly likely that over time a bad battery can kill a good alternator, and vice versa. So if there is any question, replace both.

 

That could be the case...the little old lady who owned it prior would let it sit for months on end and she told me she had to replace the batter a few times after the car came out of hibernation. I'll find out tonight as I"ll have both tested and checked and all that good stuff.

I'm off to see the wizard the wonderful wizard of Kragen, b/c b/c b/c b/c my alternator says I must.

 

Bumping this to the top, had both the battery and alternator tested last night. He said the 60amp Alt was putting out a solid 13.8 volts and the battery needed to be replaced, which doesn't surprise me. But...on the way home the volt meter started dropping again. I need a battery meter so I can tell if the battery is being drained or not and if it's just the volt meter that's screwy. So far no problems running the car so....hmm......

 

A healthy alternator should be putting out 14.4 volts, yours isn't to far off. Buy a multimeter so you can test voltages yourself. Often it may not be the components, but wiring or a current draw somewhere in the system.

 

where do you test for voltage coming from the alternator?

 

Easiest place is at the battery while the car is running.

 

and this will give me the voltage comming from the alternator?

 

Yes, it will tell you the alternator is currently charging the battery at. To see what I go test the voltage of the battery with the car off. Fully charged battery should be at 13.6 volts. Turn the car on, now check the voltage again. In an ideal world, it will be somewhere around 14.4 volts.

 

Ok so below 13.6v off is a bad or dying battery?
Below 13.6v while running is probably a bad alt too?

 

A battery below 13.6 volts isn't "fully" charged. Depends on what the reading is to determine whther it's completely dead. An alternator only putting out 13.6 volts wouldn't be too healthy. On its way out, for sure. Are you diagnosing a problem or just trying to get basic figures to work with for future reference?

 

Both, right now my current alternator has a voltage problem which is fixed with reving to about 3400 rpm at which time the volts return to usual just below the 14v mark. I suspect a dying voltage regulator since every time I turn on the car it does this.

Santiago

 

The voltage regulator is built into the alt, right? My alt meter keeps dropping down a bit, but the car runs fine with no problems. Except the stupid clock won't keep time, but I hear that can be cold soder problems.

Can a dying alt ruin the ecu or any other electrical systems? Maybe I should just go ahead and buy an FD alt and hold onto it until this one goes. I may have to go buy a multimeter or check all the damn connections to make sure nothing is loose. Of course I'd hope that's the problem, easiest cheapest fix.

Otherwise the car runs perfect.

 

I just checked my car at home and I got 13.86 to 14v when runing.