yet ynother VR, Alternator, idle voltage thread...

[1974PlymouthDuster]

On the 74 Duster with 318, I have been steadily increasing my idle voltage troubleshooting steps...

#1 - Sanded and filed down fender holes and Voltage Regulator holes.
#2 - Dielectric grease on terminals of Voltage Regulator
#3 - Switched between three voltage regulators I have kept on hand
#4 - Ran #4/6 gauge wire from alternator stud to hot terminal of starter relay

All these resolutions (From reading post after post about this) left me with the same 14-15v idle voltage.

Unplugging the VR (any of the 3 VRs I have) seems to set idle voltage right at 14v
**one of the VR's leaves me with 15v idle voltage, and 16v revved voltage (pulled that one out quick)

Revving the engine above 1,000 rpm leaves me with a nice steady 14v too - This resolves all my issues with all VR's I have tried.

I have a squareback alternator, but I do not know what the actual/advertised output is. I do recall recently having this and an alternate alternator tested at Autozone, but I dont really trust these results.

Is this the stage where I just pony up for a upgraded alternator, or even just go 1-wire? I have also looked for a upgrade rebuild kit, but these seem to be out of stock everywhere I have looked.

Let me know if there is any other troubleshooting I can attempt? Thanks guys - FABO has been such a resource for our Duster and Valiant !! (see Members Restoration for my name)

-Ryan

 

[67Dart273]

Here's how this works, depending on what wiring you have / have not modified.

The regulator POWER comes from switched ignition, and ANY voltage drop, either in the ground leg, or the ignition "hot" harness

now ..........I said ...........voltage DROP

But what this DROP does is actually INCREASE voltage "at the battery"

Plant this in your head, based on factory wiring. The regulator gets ignition power (and this is also the "sensing" voltage

GROUND PATH. Battery NEG.........through the cable.........to wherever it's grounded to body..........through the body..........to regulator mounting flange.

IGNITION................. Battery...........battery cable...........starter relay battery stud..........fuse link..........through the bulkhead............ammeter connections..........through ammeter...........through "in harness" welded splice..............ignition switch connector..........through the switch.........back out the switch connector...........(on ignition run buss)...........back through bulkhead connector..........and to switched loads under hood including regulator.

NOW. If EITHER the ground or the 'hot' path have a little drop, let's say, .5 (1/2) volt. The regulator SENSING (ignition) terminal "sees" that low voltage, and ramps up alternator voltage until it is correct........at 13.8V or whatever.

BUT BECAUSE we have that 1/2 volt drop from the sensing terminal back through to the battery, this 1/2 volt is ADDED to the 13.8V regulator point, so the battery is now running at it's terminals at 13.8 + .5 or 14.3V

Of course the .5V is just an example. How to test?

I've posted this before.

Turn the key to run, ignition OFF. Hook your voltmeter to battery POS (like the starter relay stud) and the other probe to "switched ignition" You can backprobe the blue alternator field wire, or you can get the correct terminal (switch side) of the ballast resistor.

What you are hoping for is a very low reading, the lower the better, and hopefully, less than .3V (three tenths of one volt)

You must also check the GROUND

This time, run the engine at "fast idle," with battery fully up, and perform this check with all accessories off, and again with lights, heater, etc, on.

Clip one probe of your meter to battery NEG clamp. Stab the other probe directly into the mount flange of the regulator. Be sure to "stab" through chrome, paint, rust. Once again, you are hoping for a low low reading, zero is perfect. Again, over .3V means there is "drop" in the ground circuit.

You can also .............

Add no10 or larger ground jumpers from the block to the firewall to the regulator mounting bolt. There's a bolt on the rear of the driver side head (look at the front of the pass side head!!!)

On the ignition end of things, one solution is to remove all loads at the firewall side from the ignition buss and use the output from the key to fire a relay, fused off the starter relay, and use that relay to supply the alternator field, regulator, ignition system, etc under the hood.

Some additional ways to explain

If you have the engine running and measure battery voltage, and it's 'high' but you then measure "ignition run" voltage coming out of the firewall, then you know you have a "drop" problem.

This could ALSO be a bad connection at the regulator connector, make sure it's clean and tight

In rare instances a battery problem can cause this. Easy if you have "other cars" and can swap batteries temorarily