Fueling imbalance

Ideally, it requies determining which bank is at fault. You can do this through the on-board function, somewhat different than the commands you used to obtain the code. After the codes display, you should see ECM? on the display. I think high fan and low fan are the buttons you will use, whichever button scrolls, the opposite selects. From ECM?, you want to select ECM so press one of the buttons. If it changes to another module, scroll until you get back to ECM?, and press the other button. You are looking for ECM DATA?, once you find it, select it. It will go through numbers like ED01, ED02, and so on. The oxygen sensor data is ED34(left), and ED35(right). Check for the voltages to be swinging from low to high when running it up at operating temperature. If you have a sensor sticking low, or high, it indicates a rich or lean condition on respective bank. 91 had problems with injectors shorting, and that could cause a fueling problem, that is just food for thought. It could also be indicative of exhaust or vacuum leaks, faulty secondary ignition(misfire). To the best of my product knowledge, this is correct in the on-board functions. If it seems incorrect, or you have trouble, reply to this post and I will research it from a paper manual.