71 Dart overcharging

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dusterdragracer

dusterdragracer

Drag Racer
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My wife's 71 SB Dart overcharges.
All the usual issues have been checked.
Checked with meter so it is real. 15.5 volts at battery.
Doesn't come down after driving it
Replaced Alternator
Replaced 3 different regulators, all new
Ran temporary power and Field wires from alternator to regulator, to bypass factory wiring.
Correct ballast resistor in place.
Only thing not stock is, the battery is in the trunk
Good grounds
Good heavy battery cable direct to relay.
I also have a heavy wire from when we raced it, that goes direct to the battery from the alternator, eliminating factory wiring. I can run it on either wires, factory or direct
Still 15.5 at the battery
Any suggestions?
 
Have you tested the battery? If it is bad, it will draw the maximum current it can from the system. Also check all of your connections to the battery.
 
And after you do that (the above) make some voltage checks

I don't know how you have your cables wired, so you need to itemize, that is exactly what and where is the grounds, and what size, and how large is the POS and how large

This is LIKELY to be 'voltage drop' at the VR

With the VR powered, and engine off, measure voltage from the VR case to the VR IGN terminal. This voltage should be as close as possible to "same as battery" and if it's off by more than .2--.3V (3/10 of one volt) that is the problem

Same with ground. Get the thing running and charging "fast idle." Using an extension wire, hook a wire to the battery NEG post. Run this up front, and hook that wire to one probe of your multimeter. "Stab" the remaining probe into the VR mounting flange. Again, you want to see LESS than .2V, the less the better. Then repeat the test with whatever heavy loads you can turn on, heater, lights, fans, whatever.

NEARLY forgot.......disconnect the VR and make absolutely sure the VR actually has control. It should stop charging.
 
Good info. I will load test the battery tomorrow, but I think it's O.K.. The connections are very good. That is always my #1 test.
Cables I believe are 'O' (read huge)
The other tests are interesting.
VR is working, with lights on, heater etc. follows the 15.5 charging
I am going to guess, having the battery in the trunk, is causing a voltage drop to the VR (via ign. switch). I did see that kind of drop at the VR. Never heard that one before,cleaver. I have tons of old Mopar repair books, must have missed that one.
A relay, ignition activated, and a heavy wire from the batt. or batt. cable to the VR would solve that issue, if that turns out to be it. Its all right there together.Simple
Stay tuned!
Thanks,You guys got me thinking.
PS. rustyratrod, love those scriptures
 
67dart273's instructions helped me diagnose the overcharging in my '72 Scamp with the voltage drop test; I'd never encountered that issue before so it was very helpful to have the expertise at your beckon call...found out there was a 2V drop between the ignition switch and the battery, which creates the difference sensed by the VR, and leads to the overcharge condition. When I tried to replace the ignition harness, I ran into issues so I just installed an ignition relay--all overcharge problems went away, and system voltage dropped down to about 14V~14.5V IIRC.
 
txstang84 said:
67dart273's instructions helped me diagnose the overcharging in my '72 Scamp with the voltage drop test; I'd never encountered that issue before so it was very helpful to have the expertise at your beckon call...found out there was a 2V drop between the ignition switch and the battery, which creates the difference sensed by the VR, and leads to the overcharge condition. When I tried to replace the ignition harness, I ran into issues so I just installed an ignition relay--all overcharge problems went away, and system voltage dropped down to about 14V~14.5V IIRC.
Click to expand...


Thanks, you verified what I was going to do, works. Simple fix with a bosh relay.

Just a side note for others who may read this. I had a MSD ballast resistor installed, instead of the stock one, back from when we raced the car. it was .8 ohms. The coil would overheat, and it would die now and again. It acted like fuel loss, or flooding.
When it had that ballast resistor installed, it charge like 16.5, and the tac went crazy. So this now makes sense. As the resistance was incorrect, it caused the voltage to the regulator to be lower(ballast resistor and regulator are powered on same wire).
 
Well that shows that wire is undersized, think "overloaded." Surely you don't have the VR powered off the load side of the ballast?

What have you got for a power feed, IE you have a small wire from battery to up front, or you tapping off the starter for power? What are you using for a harness or switch?

Yep. Relay. That is one way.
 
Make sure you have a ground strap from the rear of the cylinder head to the firewall. If not, the only other ground path from the body of the car(which is what the voltage regulator and ECU use as a ground) is through the small diameter ground connection leading from the negative cable to the core support.

I've even seen later M-bodies with factory ground straps between the block and front frame rails.
 
67Dart273 said:
Well that shows that wire is undersized, think "overloaded." Surely you don't have the VR powered off the load side of the ballast?

What have you got for a power feed, IE you have a small wire from battery to up front, or you tapping off the starter for power? What are you using for a harness or switch?

Yep. Relay. That is one way.
Click to expand...

Haven't had time to look at any thing. The wiring is stock. Yes, power for ballast, and VR are on same source which is stock (per factory wire diagrams). The batt. in the trunk is the only non stock part of the system. It is wired from same location at the relay (or starter) as the stock batt cable, just a heavier and longer to the trunk. Engine is grounded to fire wall via a batt cable. I married into this car, most of this was done before me. I cleaned a few things up.
Going to check it out tomorrow, and will post. Thanks Guys
 
Just for curiosity, why would a .2 volt to .3 drop make any difference when not running? The regulator comes into play when the engine is running, therefore the voltage goes up, and the voltage becomes the same at battery as at the regulator. I had to think about that one.
There is always going to be a drop when not running through the ign. switch, because of things like the resistance from the switch, wiring, connections, guges etc. Especially when the batt. is in the trunk.
I did try a wire from the batt. cable, to the regulator, which made the voltage the same at the regulator as the battery 12.5 not running. Made no difference in the output of the alt. when running
It's all good now, it is charging 13.9 at above idle max. The .8 resistor was the issue. It had been sitting after I thought about it. The battery gets down because it has a memory stereo. It also has a Holley with an electric choke. Once it ran awhile the voltage came down. I also discovered the aftermarket gauge is about .3 higher then the real voltage with my Fluke.
Thanks for all the input
Chris
 
Here's how this works. You can either measure the drop with the key on and engine stopped between battery and VR, or........

You can measure the difference between actual battery running voltage and the VR power (IGN) terminal while running.

So long as there are no other drops in the system, the above two readings will be the same

This is because The VR regulates the IGN terminal (the sensing terminal) to the VR setpoint. If you have a .3 drop at the VR, then the VR ADDS this to it's setpoint, so that if it is set for 14, the battery "run" voltage becomes 14 + .3 = 14.3V

But the GROUND circuit also must be accounted for, so if there's another .1 or .2 or whatever it might be, THAT also is added. Most of "these old girls" have more than that in the hot harness

Your original circuit path to the VR is this "map" Battery.....fuse link.....BULKHEAD CONNECTOR.....ammeter........welded splice...........IGNITION SWITCH CONNECTOR.........THROUGH THE SWITCH..............BACK OUT the SWITCH CONNECTOR..............BACK OUT the BULKHEAD CONNECTOR

Everything in caps is "likely suspects" and in a few cases the ammeter and welded splice are as well. Many guys on here with overcharging had 1/2 volt OR MORE drop. My own car, right after I bought it "dead stock" was charging at 15.5 volts!!!! It had 1.5V drop in the wiring harness!!!
 
67Dart273 said:
Here's how this works. You can either measure the drop with the key on and engine stopped between battery and VR, or........

You can measure the difference between actual battery running voltage and the VR power (IGN) terminal while running.

So long as there are no other drops in the system, the above two readings will be the same

This is because The VR regulates the IGN terminal (the sensing terminal) to the VR setpoint. If you have a .3 drop at the VR, then the VR ADDS this to it's setpoint, so that if it is set for 14, the battery "run" voltage becomes 14 + .3 = 14.3V

But the GROUND circuit also must be accounted for, so if there's another .1 or .2 or whatever it might be, THAT also is added. Most of "these old girls" have more than that in the hot harness

Your original circuit path to the VR is this "map" Battery.....fuse link.....BULKHEAD CONNECTOR.....ammeter........welded splice...........IGNITION SWITCH CONNECTOR.........THROUGH THE SWITCH..............BACK OUT the SWITCH CONNECTOR..............BACK OUT the BULKHEAD CONNECTOR

Everything in caps is "likely suspects" and in a few cases the ammeter and welded splice are as well. Many guys on here with overcharging had 1/2 volt OR MORE drop. My own car, right after I bought it "dead stock" was charging at 15.5 volts!!!! It had 1.5V drop in the wiring harness!!!
Click to expand...

That makes more sense now. BTW, the VR is grounded at the base via #8 wire to the block using serrated washers, this also ties the body/frame, engine together. The batt. cable to the rear is stranded welding cable (read $$$$). It works super for batt. cable, but not very cost effective.
Thanks again for your positive feedback.
Hope this post helps others.
Chris
 
The fastest,easiest test that your system is OK, and the voltage drop between the
batt. and the ign.2(dk blue)circuit is the issue,is a long jumper from the pos.post
to the front back probed in the blue wire at the alt.It needn't be heavy,it will
simply present the 15.5V to the volt sense side of the reg., it should drop the volts
at the batt. steadily and immediately.If so,proceed w/67's advice and find the drop,
and yes,hi-output coils w/low ohm ballasts WILL cause a drop in the ign2 circuit.I
just did this to a cuda,and used the blue wire at the ballast to energize an OE FWD
mopar EFI relay to power the ballast and coil stand alone,and maintain a factory
appearance w/the metal cover etc.
As far as ground issues go,and i know this is a little scary, but i have experienced
resistance across body panels.In other words,say between the cowl and main firewall
etc.,the parts are spot welded,but there is a lack of electrical integrity,just another
thing not to take for granted.
Good luck and let us know what you find:coffee2:
P.S. you didn't say what V reading at alt output post? Jumping from that to the backside of the
blue V in term on the alt should also drop the output the same as a batt. jumper.
 
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