The warning lights on my 91 NA were intermitently flashing. After a search at this forum, I decided to have my OE alternator rebuilt by a shop that specializes in starters and alternators. I installed it yesterday. With full load, I'm getting 13.8 - 14.5 volts at both the alternator post and positive battery post. If I rev the car past 6K RPM, my voltage drops to 12 - 12.5 volts (no charge from alternator). The belts are new and are NOT slipping. I also checked my cables and I'm getting nominal resistence -- cables are fine. I normally can pinpoint electrical problems, but this one has stumped me. Could it be computer related?

Any ideas would be greatly appreciated.

TODD

 

sounds like a bad diode in the retifier circuit of the alt.

Are you seeing any AC voltage on the alt output??? (hint you will need a digital multi-meter to read this).

 

Icemark:

Is the internal wiring different for S4 and S5 alternators? I'm specifically talking about the two pole harness. The shop who rebuilt my alternator stated they work on RX-7s often.

If one of the diodes is bad, should I be reading AC voltage off of the alternator post? Could you elaborate? Thanks.

TODD

 

I've been running searches on teamfc3s and RX7club all night. If the tech screwed up the two lead connector (swapped them?), would this cause my problem? In my searches, no one mentions normal charging patterns until a certain RPM, and then no charge.

Has anyone else experienced this condition?

TODD

 

Internally the circuit is almost identical between the S4, S5 and even S6 alternators (as well as every other mitsubishi built alt).

However the wire colors are different bewteen series as well as car wiring.

Yes there will be AC voltage if a diode is bad. Alternators produce AC voltage that rectified through diodes to DC voltage. Typically when a Diode fails in the rectifier circuit there will be AC voltage leaking through, normally higher amounts at higher RPM.

This is (again) the circuit diagram for the S5 and S6 alts:


S4: