I had a snap on modis hooked up to my teg recently and noticed that the ecu switches back to open loop on deceleration. I haven’t been able to determine if this is normal or not. It only does it for a second or two before going back to closed loop.
Is the car reaching operating temp? If your 02 sensor has not reached it’s operating temp, it’ll throw the car into open loop because it sees lean on the 02 side, and will dump more fuel in…
not on a heated o2 sensor. with a 4 wire,the car will go into closed loop within about 30 seconds of being started cold and stay that way until wot, or, i’m pretty sure, decel as well. since the ecm goes into fuel cut strategy on decel. i’d say that’s a normal occurance