SC O2 sensor causes starting problem
 

Hello everyone from a first time poster and my thanks to all for the help I have already gleaned from this forum. I am trying to fix my friends recently purchased '81 SC with CIS. After fixing five vacuum leaks, the distributer, and re-adjusting the mixture the car now idles and drives well with the O2 sensor disconnected. Dwell meter shows 65% at idle and mixture is a bit lean (15.5 to 16). If I hook up the O2 sensor the mixture goes to a perfect 14.7 at idle and at higher speeds. If I then turn the car off with the O2 sensor hooked up and let the car sit for 10 minutes it will not restart - it sputters and coughs but doesn't run. I noticed that while doing this there is no movement on the dwell meter. If I then unhook the O2 sensor the car restarts no problem. What is going on here? All suggestions are appreciated.

hot start problems are often caused by residual fuek pressure bleeding down, due to a faulty fuel pump check valve and/or accumulator. can't think of how the O2 sensor would have anything to do with it, but it's early and the brain needs coffee. do you have a CIS pressure gauge?

Thanks for your quick response. The strange thing is it starts immediately with the O2 sensor disconnected. It acts as though the ecu doesn't start operating the frequency valve with the O2 sensor hooked up.