Voltage regulator/alternator help

[fishmarket]

I have a '71 roadrunner 383 auto, that just fried a battery after about 300 miles. The voltage at new battery at idle was 17.5 volts... ouch. I swapped in a voltage regulator from one of my other cars and it now reads 14.5-14.6 at idle. OK, I can live with that. I decided to try another VR that I had laying around just to see if it was a little lower voltage than the previous one. I had the queen hold it to ground while I measured the voltage rather than unbolt the other one and remount this one. This one measured between 14.8-15 volts. This is where it gets odd... I asked the wife to remove it from the ground just to see what would happen. Voltage went to 12.8 (battery voltage) but the car had a slight misfire and shake at idle, that totally cleared up when the alternator/Voltage regulator were taken out of the equation. It has never ran better. The alternator is a fairly fresh rebuild unit from a local shop. I have an MSD digital 6al, with firecore distributor and wires. The engine harness was replaced a few years ago with a new one. Also have the MAD electrical ammeter bypass, it was a new mopar electronic voltage regulator and cleaned off the paint on the back and off the firewall for a good ground, now replaced with an older unit. I am at work tonight so I can't really help with much more information until tomorrow. To further complicate things, I am leaving for Moparfest Saturday morning in this car. Any idea what would cause the rough running and why it cleaned right up after bypassing the alternator/VR?

 

[Murray]

You had a VR at 14.5, what is the problem?

 

[MadScientistMat]

I wonder if the MSD 6 is having issues with alternator noise? If it isn't grounded straight to the battery, try that. Grounding to the block (or worse, the chassis.... the difference between Santa Clause, the Easter Bunny, and a good chassis ground is that some good tuners believe in Santa or the Easter Bunny) can cause digital electronics to have noise issues in some cases.

 

[fishmarket]

You had a VR at 14.5, what is the problem?

I had a regulator at 17.5 and swapped it out for one that is around 14.5 but consequently noticed that the car runs better when the alternator/Voltage regulator aren't in the mix. Misfire at idle when voltage regulator is grounded to firewall. No misfire when voltage regulator is not grounded...

 

[fishmarket]

I wonder if the MSD 6 is having issues with alternator noise? If it isn't grounded straight to the battery, try that. Grounding to the block (or worse, the chassis.... the difference between Santa Clause, the Easter Bunny, and a good chassis ground is that some good tuners believe in Santa or the Easter Bunny) can cause digital electronics to have noise issues in some cases.

I previously had a pertronix ignition, then a mopar electronic ignition, now the MSD. Car had the misfire with all 3. Ill try grounding it straight to the battery and see.

 

[67Dart273]

Regulator MUST be grounded, and I mean to "same potential as battery."

Here are the issues:

The solid state VR's used 70 and later are TEMPERATURE compensated, and that means that you must check them after things are warmed up. If you get into section 8 of the manual, somewhere in there is a chart showing that. The "go to" warmed up (with battery stabilized) running voltage is 13.8--14.2. 14.5 should be livable

The VR MUST be grounded, but that does not mean that the body/ firewall is well grounded to the battery. I Look at the pass. side head. Those bolt holes on the front of the head are also on the REAR of the driver's side head. Buy a Ford starter cable, 1'--1 1/2' or so, bolt it to the head with a short bolt (be sure not to bottom it) and bolt the other end to a good point on the firewall. You may have to drill a hole and bolt it, star lock washers. Another place is often the master cylinder mount studs.

The ignition "run" line normally dark blue which powers ignition, the VR, electric choke if used, etc, often has VOLTAGE drop in the harness, and that causes over charging. Common points of drop are the bulkhead connector terminals, the ammeter terminals, the ignition switch connector and right in the switch contacts themselves.

Again, 14.5-6 is not bad

 

[fishmarket]

Regulator MUST be grounded, and I mean to "same potential as battery."

Here are the issues:

The solid state VR's used 70 and later are TEMPERATURE compensated, and that means that you must check them after things are warmed up. If you get into section 8 of the manual, somewhere in there is a chart showing that. The "go to" warmed up (with battery stabilized) running voltage is 13.8--14.2. 14.5 should be livable

The VR MUST be grounded, but that does not mean that the body/ firewall is well grounded to the battery. I Look at the pass. side head. Those bolt holes on the front of the head are also on the REAR of the driver's side head. Buy a Ford starter cable, 1'--1 1/2' or so, bolt it to the head with a short bolt (be sure not to bottom it) and bolt the other end to a good point on the firewall. You may have to drill a hole and bolt it, star lock washers. Another place is often the master cylinder mount studs.

The ignition "run" line normally dark blue which powers ignition, the VR, electric choke if used, etc, often has VOLTAGE drop in the harness, and that causes over charging. Common points of drop are the bulkhead connector terminals, the ammeter terminals, the ignition switch connector and right in the switch contacts themselves.

Again, 14.5-6 is not bad

Thanks, I will run a ground directly to the battery to see if it makes a difference as well as the ignition run line. I understand that the regulator must be grounded... My wife was grounding the VR case by hand just so I could check voltage at the battery on that particular unit, as I had a few different ones to try. To my surprise when she removed the voltage regulator from the bare metal on the firewall, with the car still running, my idle totally smoothed out and a persistent misfire went away. Its gone when running only from the battery. Ammeter is bypassed, bulkhead connector is drilled out, and using a direct heavy gauge wire as per the MAD electrical modification. Ignition switch and wiring is all new as well.

 

[67Dart273]

This very well could be ignition interference.