Shielded plug wires (CIS)
 

Is there a reason that shielded plug wires are OE for 911s with CIS? They seem to have occurred and disappeared at the same time as CIS, but since CIS is a mechanical injection system I don't understand what would make shielded wires necessary.

I think mainly to decrease crossfiring on the already backfire prone CIS system. I went back with the regular wires on my '83. No problems. No oxy sensor and run it a tad on the rich side. No popping.

The non-shielded wires were not standard OEM on my 73.5 with CIS although when I bought the car they were onboard. I changed them out for the OEM black factory units that work just fine. Besides the OEM black rubber units are far less expensive and do the same job!

Regards
Bob