Coils, Ignition, and Resistors....putputput

[abe3.0CSi]

I have a 73 3.0CSI with a L Jetronic and engine from an 81 633i. Car idles a little rough...always has. Points, distributor, timing, plugs..all okay. So, I checked the blue coil voltage 9.0v and internal resistance 1.4 ohm. The ballast resistor connected has 1.8ohm.
Well, after reading Pertronix troubble shooting section, 2002 site, and w113 pagoda site feeling is that a happy system has 4-8amps. After bypassing the external resistor I had 9v/1.4ohm 6.4 amps. Doing that created a smoother engine more power and virtualy eliminated the rough idle. BTW, the blue coils are made in many different countries and their internal resitance varies significantly...I know the old black and new red hot coils do require external resitance. My coil does not heat up..a risk if too many amps going through.
Soooo,, check those sites learn how to check voltage at the coil, and resistance....you may end up with a happier iginition system. BTW, I do not have pertronix...just used them for education.
abe

 

[HB Chris]

The blue coil does not need an external resisitor, it is internal as I understand. Great post!

 

[bill]

My 74 CS, manufactured in Oct. 73, does not have a ballast resistor, and it has a blue coil. But, instead of a ballast resistor, it has a resistance wire. The resistance wire can be identified as the clear insulation wire (well, somewhat yellowed, after 36 years) connecting to the + side of the coil. I would suspect that problems would occur if a ballast resistor were added to the ignition power supply already ballasted with a resistance wire. Removing the ballast therefore would explain the improved operation, n'est-ce pas?

 

[abe3.0CSi]

The blue coil does not need an external resisitor, it is internal as I understand. Great post!

Yes, ...but mine was attached to one thus the decrease in performance and idle issues. However, there are many blue coils today from Germany, Mexico, Eastern Europe....and they all have different resistance thus different amps. There are even a few blue coils out there too with no resistance thus requiring an external resistor...never seeing it but heard about it. Mine probably has that resistance wire that is why it read 9v instead of 12v. The pertronix has great instructions on how to check it....might be worth while.
One last thing....my approach is rather simplistic. Keep in mind that each coil will generate different Kvolts thus some require less voltage than others. Thats why the red uses ballast resistance..with its higher kvolt
it needs less voltage at is primary.
What I learned .....a restorer or a mechanic is not going to look into every little detail.
Most will just assume that everything before was done correctly so why look into it. Thanks to a
little education...look why I discovered!!!!

abe