I've never seen the dwell change with RPM's on any car I have owned that uses points. If you are seeing this, you may have some real bad play in your distributor. (Or you are measuring readings from a car with electronic ignition)
The only way you have heat buildup at the ballast resistor, is due to increased contact resistance as a result of corroded contacts.
The ballast resistor's function is to limit the current that goes through the coil when it is charging up in between firings. As a result of this, the voltage should always be B+ which is the voltage of the charging system. Depending on year and model it can range anywhere from 13.8V to 14.4V.
(Unless you are measuring a modern electronic ignition module with soft start that pulses at 6-8 V before engaging the starter.)
Chris Middlebrook
1962 Custom Southampton
--- On Thu 12/28, < sosmi@xxxxxxxxxxx > wrote:
From: [mailto: sosmi@xxxxxxxxxxx]
To: mailing-list@xxxxxxxxxxxxxxxx
Date: Thu, 28 Dec 2006 16:05:57 +0000
Subject: RE: IML: resistors and voltage
The ballast resistor, varies in resistance,do to heat. At low speeds, the resistor is hotter, due to longer periods of point closing (contact) the resistance is greater, resulting in lower voltage across the points.
As engine speed increases, the resistor cools, and voltage increases across the points, but the contact time is reduced.It would be quite normal to see 6-8volts at idle speeds, and 10-12 volts, at high speeds.Ya'll have a nice day, Dave.
-------------- Original message --------------
From: "Michael O. Mann"
I haven't seen all the comments and am coming into it late, but was confused by Chris' voltage readings.
IF I understand correctly, the resistor drops voltage, and is wired such that it is bypassed during the start sequence. Full voltage is available when you light off the engine, but slightly less voltage is provided at all other times. Bypassing the resistor temporarily will give the car a much hotter spark, but will burn the points badly within a few days. If you do this three times before you learn, it will burn the points three times. But that is another story.
Resistance across the MOPAR
ballast resistor is about 0.5 ohms, if memory is working. Voltage on the battery side should measure above 12V, around 13-14, if all is well. The other end should be closer to 10-12 volts; six sounds low to me. Can't find the FSM to be certain. Will look more.
I didn't quite follow the test results, but with everything hooked correctly,and the car running, measure voltage to ground on the battery side of the resistor, and then on the other end. This is a cheap part, and easily replaced. If you have any uncertainty, replace it. If it's cured, buy another and put it in the spare parts bin. If not, leave it in place, and put the one you removed in the spare parts bin.
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What about the fuel tank & lines? Is there a lot of junk in the tank that's finding its way into the carb? Any pin hole leaks in the lines that could be sucking air? I'd remove the inline filter & empty the gas onto a paper towel or something so you can see is there are rust particles in the gas.
John
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I've recently gotten some hard lessons on dirty gas. I am working with small engine equipment in Chad, where the finest gasoline comes conveniently packaged in old whiskey bottles with a rag stuffed in the top, suitable for fuel, or ready to light and throw. We lost a couple of pieces of equipment before realizing just how bad the fuel is. I strain all ga
soline twice through coffee filters before it's run. It is amazing how much very fine particulates remain suspended in fuel that looks acceptable. A little bad gas can cause you trouble for a long time.
Good luck with this.
Michael
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