I have the 6395 ecm from 94 tbi (BJLK bin).
Is it the code that swingin the co2 up and down in closed loop to
protect the cat(i dont have cat) or cant it be steady (nb).
why is it more acurat in open loop.

 

The swinging CO2 is the result of how the PID algorithm works. The stock PID algorithm purposly has the proportional term gains set up to cause teh O2 volts to swing about the long term average O2 volts. This is likely done for three reasons:

1. theres no derivative term so the algorith may be prone to ocillations.

2. this allows the routine to quickly get to the desired fueling as the integrator term alone would have a long response time and wouldnt be able to suppress transients.

3. this allows for diagnostics of the O2, as when its working properly as its output will swing back and fourth. No swinging O2=bad O2

In regular car guy terms. The closed loop stuff causes the fueling to swing back and fourth around ~14.7:1, which is why you see the swinging CO2 (O2?). When its in open loop, no corrections are being made, so the fueling is steady as its taken right off the tables and such without the corretions added in.

Its possible to have it target a steady fueling, but then there would be no way to see if the O2 is working properly, and the routine may not perform as well.