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PostPosted: Wed Aug 21, 2013 8:20 am 
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TBI Slant 6

Joined: Thu Dec 06, 2012 11:50 am
Posts: 160
Location: Thousand Oaks, CA
Car Model:
When Idling I'm getting slightly lower than 12 volts(low to mid 11s per my multimeter) at lights and accessories such as the radio. Its a pretty plane jane radio so it doesn't mind, but the lights dim when idling, and thus when i touch the gas they brighten up. I checked the fuses and pulled the ones that looked a little corroded but it made no difference. I checked the voltage before the fuses and it too is in the lower 11s instead of 12.

Some of you may remember that I just couldn't get my idle down, well I've tracked this to be the issue. The idle is going down, but when the voltage is that low the tach reads artificially high for some reason. If i tap the gas the tach drops to the correct reading then starts to rise with the engine speed as expected.

The battery does hold a charge and is relatively new. On the few occasions I've killed it when tinkering I've jumped it and driven around a bit and it does charge up nicely. At idle however the Ammeter is usually pretty much dead on in the center. If I turn on lights it goes below center indicating a drain.

Does this point to alternator? I've done some searching and some people pointed at the voltage regulator. Where should I start? Are the tests at auto parts stores for the alternator worth my time?

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1968 Plymouth Barracuda [Daily Driver]
1972 Dodge Dart Swinger [Lent out as Daily Driver to a friend]
2010 Challenger R/T 6 Speed


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PostPosted: Thu Aug 22, 2013 8:34 pm 
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TBI Slant 6

Joined: Thu Dec 06, 2012 11:50 am
Posts: 160
Location: Thousand Oaks, CA
Car Model:
Got a new Echlin VR, which btw are made in china now.. but carry a 3 year warranty. Didn't fix the problem. I also checked all the grounds, still low at idle. I'm guessing it is just the alternator going at this point. Bummer. Probably wasn't bad to replace the old one, as it looked pretty gnarly.

Image


Would the ACDelco 60amp from Rock Auto be a decent way to go?

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1968 Plymouth Barracuda [Daily Driver]

1972 Dodge Dart Swinger [Lent out as Daily Driver to a friend]

2010 Challenger R/T 6 Speed


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PostPosted: Thu Aug 22, 2013 8:41 pm 
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TBI Slant 6

Joined: Thu Dec 06, 2012 11:50 am
Posts: 160
Location: Thousand Oaks, CA
Car Model:
Quick Q, what voltage should be seen at the + of the ignition coil in standard electronic ignition setup? I'm seeing like 6.3 volts at idle. Sounds about right?

_________________
1968 Plymouth Barracuda [Daily Driver]

1972 Dodge Dart Swinger [Lent out as Daily Driver to a friend]

2010 Challenger R/T 6 Speed


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PostPosted: Thu Aug 22, 2013 8:47 pm 
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Supercharged

Joined: Thu May 12, 2005 11:50 pm
Posts: 6291
Location: So California
Car Model: 64 Plymouth Valiant
The older (early/mid 60s) alternators only had 35 amps so this was common.


You could put an ammeter on the output line and load test it...........

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

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PostPosted: Fri Aug 23, 2013 6:32 am 
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Supercharged

Joined: Sun Jun 04, 2006 4:53 pm
Posts: 4295
Location: Gaithersburg MD
Car Model:
Check the high side of the ballast resistor. It should be the same as the alt out put. I thought 8 volts on the low side was normal, but my ignition does not use one any longer.

Sam

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PostPosted: Fri Aug 23, 2013 8:02 am 
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Supercharged
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Joined: Sat Feb 16, 2008 1:25 pm
Posts: 5599
Location: Downeast Maine
Car Model:
Quote:
Got a new Echlin VR, which btw are made in china now.. but carry a 3 year warranty.


Keep an eye on that new regulator, if you see amp gage peg to (+) and then back to center for a few seconds, remove replace that regulator. I installed one a few summers ago and it would drive alternator to full out-put at idle rpm causing alternator to emit strange sound, and then back to normal after just a month of use. After a few of these bouts, I figured out that the regulator was faulty, and replaced it before burning up my cars wiring harness.

A few ideas to kick around:
One fix for poor low rpm alternator out-put is to upgrade to a square back 1970 + stile alternator with two field terminals. All one has to do is ground one of the field terminals (doesn’t matter which one), and reconnect existing harness wires same as they were on old alternator.

Another possible fix is to have alternator tested under load, and replace parts such as brushes and or diodes as needed to restore its performance.

Quote:
I checked the fuses and pulled the ones that looked a little corroded but it made no difference. I checked the voltage before the fuses and it too is in the lower 11s instead of 12.


From this statement I conclude that your electrical harness needs some TLC to remove as much corrosion at connections as possible. Corroded connections introduce resistance to any circuit and acts to serve as an additional load on that circuit not unlike adding an additional lighting device, or small motor.

Before making any changes, and spending any money on parts such as a VR, first take the time to clean and remake all connections in lighting circuit including all grounding points. Increasing the size of ground wire to head lights, little black wire attached to body of car behind each headlight bucket & parking light, and running a 10 gage ground loop picking up these grounding leads back to negative battery terminal will somewhat improve headlight performance.

Your battery should be able to bridge the low output gap from alternator at a stop light if it is up to snuff provided all connections in harness are clean, and free of voltage drop.

A more costly up grade, but a very effective improvement is to increase conductor size to headlights, and power them directly from battery via a relay system triggered from headlight switch. This fix eliminates all bulkhead connector’s weak points & resistance added from under sized conductors that factory bean counters mandated to save 2 cents per vehicle going down the line, and allows for full voltage to lamps.

I installed this headlight relay system a few years ago using Dan’s parts, and my wire, and the improvement using my existing off the shelf halogen lamps was dramatic; about 1/3 brighter.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

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