CSi coil confusion.

[Cornishman]

I have a late CSi which is running on original contact breakers, the coil looks very old and has a red / orange top and is branded Bosch. I can't see a ballast resistor anywhere and not sure which wire to measure to see if that is the resistor.
I had a misfire so tried to change all the easy bits, points, plugs, condenser and finally cool. But what type of coil do I use?
My local motor parts place sold me one that was supposed to be correct. However the box it came in said that it is 12v, I am told by a reliable source that it should run a ballast resistor and a 9v coil.
Can anyone explain this to me and which coil they think is correct?
Thanks
C

 

[Christopher]

The late model didn't have a resistor Charles. Will check the spec on my coil and let you know

 

[John S]

Bosch Coil

The later model csi ('74 and up) have a 0.9 ohm resistor wire instead of the ceramic ballast resistor (it looks like clear/yellowed speaker wire). The stock coil is the one that requires a 0.9 ohm resistor. The BMW part number of that Bosch coil is: 12-13-1-357-294. They are often referred to as the "Black" coil, but are actually silver with a green sticker on them now. My original coil (which is black) has the Bosch part number 0 221 119 016 which is now superseded to Bosch part number 0 221 119 021. Sometimes called the Bosch 00010 coil (About $44.00 from AutohausAZ). Don't order the part from BMW because you'll end up getting the exact same Bosch coil, but it will cost about twice as much. These coils are 12 volt, not 9 volt, and require 0.9 ohm resistor.

Hope that helps,
John

 

[Ohmess]

You can tell the difference by measuring the resistance through the coil. The coil with the 0.9 ohm resister will measure 3.1 ohms across the terminals. The coil without will measure 2.2.

 

[John S]

Coil type

Or you can look at the Bosch part number stamped on the bottom of the coil to see what coil you've got in their now.

 

[Cornishman]

Thank you, worked it out.

Thank you for all the information, with it I worked out how the coil wiring works, so could do a real test on the circuit. John S the speaker wire ballast resistor information was very valuable, thank you.
However the fault got so bad that in the end it would only run on start up for a second or so. I eventually worked out that this was from the cold start valve.
After checking many things, changing many parts and doing more tests I got a more accurate multimeter. Doing a resistance check opening and closing on the points and then each pair of FI points I noticed that they were not even. So as a final kill or cure I put the FI points assembly into a petrol bath. Now she runs again.
Road test is so far so good, with luck I will be at Gaydon in the morning. May be with a tow truck, but she seems ok at the moment.
Thanks for the help.
C