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Dwell 28 degrees


maok
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Hi all, I'm having a very interesting problem with my '36 Airstream C7, the ignition dwell is 28 degrees not 38 degrees. The distributor has a Pertronix module and has been running flawlessly for the last 18 months when I installed it, but just the other day the car starting running bad, will start but runs very ordinary. Has anyone experienced this before?
 Interestingly my timing gun doesn't work well with the car running like this, its intermittent, I assume its due to the lack of voltage along the spark plug lead due to the dwell being so short (28*) and its not trigging the timing light. I've checked the usual things, ie. 12volts to the module, leads, cap, rotor, coil. Could it be my dwell meter...lol

 

Its got me puzzled.

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I may stand corrected, but dwell is used for points ,not electronic ignition. It measures the amount of degrees the points are closed. You may want to check your air gap on the pertronics.

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Dwell measures the amount of time a coil is charging up, it is applicable to points or electronic ignition.  Low dwell means that the spark will be weak.

 

Petronix has what they call adaptive dwell control, they give no numbers though.

 

https://pertronixbrands.com/blogs/product-higlights/understanding-ignition-dwell

Edited by Sniper
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Putting your dwell readings aside, most of the Petronix modules I've tossed crapped out between 1-2 years.

If you're already 12v, I would change over to the slant 6 conversion with a GM 4 pin module and keep the Petronix coil.  Bullet proof and replacement parts are everywhere.

 

Just a thought...

 

EDIT: In my experience, I would sometimes see fluctuating timing at idle when the modules were on their last leg along with higher RPM missfires.

Edited by Adam H P15 D30
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OK so everyone what to convert to 12v and Pentronics ignition.  So I have a 1939 Desoto that stillhas the original dizzy - Autolite with the points and condenser and rotor.

 

Last week we drove over 550 miles from Philadelphia area to Altoona PA for the National Desoto Car show and convention.  I  checked my standard old style ignition setup.  I saw that my cap had some wear on the contacts, so put on a NOS dizzy cap with the brass contacts. Clean the points and set the gap with a tool called a SnapGap tool made it so simple to set the points. The contact does not have to be on the tip of the cam.

 

Set the points at 20. installed the cap starte the engine let it come back to ide setting checked the dwell and I was at 35. the specs call for 35-38. so i left the setting just where is was set.  We ran the Pa turnpike averaging 50-53 MPH all the way out and back. Averaged around 15-17 MPG with an old style ignition setup.

 

So the old points and condensor setup has proven that they can be reliable and perform as expected.  My tune up basically cost me approx $25 becsue I had the parts.

 

Also cleaned the sparkplugs and when got home checked several and they had the gray color to them at the tip running Autolite A9 plugs.  So why would I switch to electronic ign? i have owned the car for 35 years with the original ign components, go figure. 

With this tool I can adjust the points while the dizzy is inthe engine block and it took me approx 5-10 minutes max

If you want more information contact me at Desoto1939@aol.com and i will explain how simple this took makes setting your point.

 

Rich Hartung

 

 

image.png.83a95efb3e1f1a1b3733d7dc48c08b33.png

image.png.b27c029263202333e8adbd4791a34297.png

 

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I didn't know Petronics did that, but it sounds similar to the GM function.  They limit dwell at low speeds.  that is one of the reasons they operate at a full 12v, the dwell limit also controls current flow and coil heat as a result.

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2 hours ago, DonaldSmith said:

Can a body keep his car at 6 volts, and run the ignition off a 12 volt inverter? 

 

I don't think that would work.  The inverter would be taking 6v positive ground and turning it into 12v negative ground.  The GM module, or even the Mopar setup if you went with that, is going to want to see 12v negative ground.  Since the ignition system will be using the same ground path as the 6v system I suspect that they will not play together well.  Now if you had a 12v system isolated from the 6v system (such as a stand alone battery) then I think it would work.  But I suspect that the inverter would not like you connecting it's 12v negative ground out put to it's 6v positive ground feed.

 

Caveats here, I haven't tried it, not 100 sure it wouldn't work, but strongly suspect it won't.  If you try it make sure you put a fuse on bot legs of the 12v circuit to prevent smoking your inverter. 

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4 hours ago, DonaldSmith said:

Question to the /6-GM-module gurus - 

 

Can a body keep his car at 6 volts, and run the ignition off a 12 volt inverter? 

 

It depends on the inverter.

 

1 hour ago, Sniper said:

 

I don't think that would work.  The inverter would be taking 6v positive ground and turning it into 12v negative ground.  The GM module, or even the Mopar setup if you went with that, is going to want to see 12v negative ground.  Since the ignition system will be using the same ground path as the 6v system I suspect that they will not play together well.  Now if you had a 12v system isolated from the 6v system (such as a stand alone battery) then I think it would work.  But I suspect that the inverter would not like you connecting it's 12v negative ground out put to it's 6v positive ground feed.

 

Caveats here, I haven't tried it, not 100 sure it wouldn't work, but strongly suspect it won't.  If you try it make sure you put a fuse on bot legs of the 12v circuit to prevent smoking your inverter. 

 

The custom auto sound 6v+ to 12v- inverter I installed in my old Plymouth to provide power for charging my cellphone and running a dashcam is fine with a common ground. It would likely work to power a 12v ignition system as long as the total wattage required was within its capability.

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Maok

 

Have you checked the air gap to the Pertonix.  It has some need to be within a range..

 

Not knowing what your particular set adjustments but can it slip out of adjustment just like points sometime do??

 

DJ

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1 hour ago, DJ194950 said:

Maok

 

Have you checked the air gap to the Pertonix.  It has some need to be within a range..

 

Not knowing what your particular set adjustments but can it slip out of adjustment just like points sometime do??

 

DJ

 

Thanks DJ, this is what I have been wondering, though,  this kit is design to fit where the condensor locates into, ie there is no adjustment as such, screws into place in one position.

I am going to bore out the holes in the plate of the module and adjust it closer to the shaft today, hopefully it works.

 

Image 1 - Pertronix Ignition Ignition Conversion Kit Ignitor Points to Electroni… (2563LS)

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With the holes drilled out and the module moved closer to the shaft, made no difference.

 

So I installed the points and condensor, after a few points gap adjustments, dwell is back to 38*, the car is running much better. The 38 Weber still needs tuning but its much better.

 

Its weird that the Pertronix is creating only a 28* dwell angle, makes no sense to me. It should either work perfectly, like before or not at all. I've sent an email to Pertronix for their thoughts.

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19 hours ago, desoto1939 said:

OK so everyone what to convert to 12v and Pentronics ignition.  So I have a 1939 Desoto that stillhas the original dizzy - Autolite with the points and condenser and rotor.

 

Last week we drove over 550 miles from Philadelphia area to Altoona PA for the National Desoto Car show and convention.  I  checked my standard old style ignition setup.  I saw that my cap had some wear on the contacts, so put on a NOS dizzy cap with the brass contacts. Clean the points and set the gap with a tool called a SnapGap tool made it so simple to set the points. The contact does not have to be on the tip of the cam.

 

Set the points at 20. installed the cap starte the engine let it come back to ide setting checked the dwell and I was at 35. the specs call for 35-38. so i left the setting just where is was set.  We ran the Pa turnpike averaging 50-53 MPH all the way out and back. Averaged around 15-17 MPG with an old style ignition setup.

 

So the old points and condensor setup has proven that they can be reliable and perform as expected.  My tune up basically cost me approx $25 becsue I had the parts.

 

Also cleaned the sparkplugs and when got home checked several and they had the gray color to them at the tip running Autolite A9 plugs.  So why would I switch to electronic ign? i have owned the car for 35 years with the original ign components, go figure. 

With this tool I can adjust the points while the dizzy is inthe engine block and it took me approx 5-10 minutes max

If you want more information contact me at Desoto1939@aol.com and i will explain how simple this took makes setting your point.

 

Rich Hartung

 

 

image.png.83a95efb3e1f1a1b3733d7dc48c08b33.png

image.png.b27c029263202333e8adbd4791a34297.png

 

AS the rubbing block on the points wear, the dwell needs adjusting as well as the ignition timing.

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1 hour ago, DJK said:

AS the rubbing block on the points wear, the dwell needs adjusting as well as the ignition timing.

Part of the twice yearly tuneup.  Where I grew up you'd do a tune up in the fall to set things up for the coming winter and a tune up in the spring to set things up for the summer.  Checking dwell was part of it.  Where I live now, in addition to not having to shovel snow, I only have to do a yearly tuneup. 

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I’ve heard of connecting 2 optima 6 volt batteries together. I’m not sure if it’s series or parallel. Apparently you get double the amperage to the starter and the genny still charges both. I seem to remember the car was a 55 Lincoln and that was the owners solution for hard starting.

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3 hours ago, Doug&Deb said:

I’ve heard of connecting 2 optima 6 volt batteries together. I’m not sure if it’s series or parallel. Apparently you get double the amperage to the starter and the genny still charges both. I seem to remember the car was a 55 Lincoln and that was the owners solution for hard starting.

 

Two batteries in Series = Add up the voltages - Amperage doesn't multiply

Two batteries in Parallel = Add up the Amperage - Voltage doesn't multiply

 

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Parallel, series, Merle beat me to it.   A car battery is a positive series of 2-volt cells, 3 for 6 volt and 6 for 12 volt. 

 

For a while, I had a second automotive battery in series with the main one, to provide 12 volts for a pusher fan and electronic devices.  But it required manual charging of the second battery.  So I got a 6-volt pusher fan, and got an inverter for the electronics (GPS navigator, cell phones, etc.)  That got me wondering about using an inverter for something like the the slant 6/GM module upgrade.  

  

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My understanding about inverters it they can put out a "dirty" sign wave which sensitive electronics usually don't like.  Ignition modules are very sensitive which is why you shouldn't use mechanical voltage regulators or non resistor plugs/wires with them.

Nothing wrong with points in either a 6v or 12v vehicle with proper coil primary resistance on the 12v systems.  Only issue I see is off-shore point / condenser sets, lots of issues with those noted on the HAMB.

With 12v, the slant 6 conversion and a GM module is very reliable if you wish to go to electronic ignition, Pertronix not so reliable.  They almost always crap out exactly like the OP described.

New Mopar control boxes also seem to suffer from the off-shore blues.

Could use a Ford TFI module if you want but they had reliability issues since the 80s.

Could also use an MSD 6 box triggered by points or almost any module, but that's more aftermarket parts not always available on the road.

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Did I tell this one already?  In the '60's, Uncle Arthur traded in his '30's car and got one of those new-fangled ones, a base model Chevy compact.  He stated,

 

"Two-speed wipers, three-speed fan, I don't know what a fella needs all that for."  

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  • 1 month later...

Well the mystery deepens. After receiving a new Pertronix module, exactly the same result. It has me totally puzzled.

 

I have replaced the coil, checked all the wiring and voltage levels (12.4v) still 28* dwell. Yet, switching back to points and condensor, with adjustment of the points gap, I get the correct 38* dwell, so my meter is working correctly.

 

🤔🤔🤔

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PA, I've checked the dwell when the Pertronix was working correctly in the past, its always a rock solid 38*'ish on a dwell meter. Remember, the Pertronix is a simple replacement of the points, simply turns the coil on and off.

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and you said it, simply turns it off and on...it is a trigger only and not able to correctly display a dwell as it would in the use of points...you can get a reading...but it is not accurate.  Perhaps Pertronix says it best though you over read the line in their brochure of the product....

 

With the use of modern electronics, there is no reason to be concerned with setting the dwell of an ignition system, however the concept of dwell time still takes place in the coil. It’s just not something you need to worry about thanks to Pertronix Performance Brands

 

Understanding Ignition Dwell (pertronixbrands.com)

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