My 1990 will not go into closed loop i have scanned it and it is showing there are no codes/faults.
The oxygen sensor was reading 408 mVolts, engine temp 203.0, Oil Temp 193.5.
Manifold air Temp 134.6. Throttle sensor Voltage 0.54.
And the 02 sensor cross count was 0 with the oxygen sensor not ready.
I have Hedman hedders with the 02 sensor fitted to the collector by the no7 tube
the 02 sensor was changed last service i think the 02 sensor is not reaching 600.
Because of where 02 sensor is mounted would a heated 02 sensor solve the problem ?
your advise would be welcome

Did the system work before changing the O2 sensor? If so, then the sensor is the problem. New doesn't always mean good.

If you had the same issue before the sensor change, then I would say that you do need to re-position the sensor closer to the head, or rig up a heated sensor. With engine temps in the 200f range, and no closed loop operation, I'm surprised there are no codes...