When I first start the Rx-7, the alternator doesn't charge. After a few minutes of idling you can watch the votage gauge start dropping. If you rev the engine up to about 4k RPM's then let off, everything is fine. Volts go up, and it all works like it should till you shut it off again. I figure the voltage regulator is bad. I thought that it was an internal voltage regulator in the alternator, so I swapped it out with another one. Same problem.

Any ideas?

 

Your gauge is fucked up?

 

No, if I let it idle long enough the car will stall. I have also checked voltage at the battery with a DVOM.

 

bad ground? Or a bad alt? I really don't know. If you want i have a spare alt of two laying around you can have if you need them.

 

I already tried a new alternator. Is the voltage regulator internal to the alternator, or should I be looking somewhere else? The FSM doesn't go into detail on it.

 

I want to say its internal, but im not 100% sure

 

Could also be a bad battery.

The battery charge is necessary to enact the 'field' around the alternator core such that it will generate electricity. Without the alt field running (i.e, no battery charge), you will not be able to generate electricity to charge the battery, much less run the ignition system.

Try swapping the battery out and see if that changes things. That you mentioned it does this on start-up, but after revving seems to work better implies that the battery already has a low charge and spinning up the alternator helps to get it back to 'functional' status. The more juice you build up in the battery, the better the alternator will work at recharging it, until you shut it down, then the battery goes flat again.

My bet is on the battery. If an IC voltage regulator were to go out, it's all or nothing. The fact that it works at all is good insurance that it's not the IC voltage regulator or the alternator.

Check grounds, too, of course.

 

the regulator is internal, I have the same problem, its in the gauge

 

me too thats why I said it was the gauge...bought an aftermarket gauge...no more probs

 

Bought a new battery and that seems to have done the job.

Thanks for the help.

 

Simple things first, after that, the cheapest things.

You'll want to keep an eye on it to see if this problem recurrs, however, since if it's the alternator, it's only a matter of time (days) before your battery is dead from running everything on the car, and then you KNOW that it's a bad alternator!

Good luck,