How many o2 sensors does my 99 5.4L 4x4 have? I need to get simulators, and need to know how many to buy.

you dont need simulators if you get high flow cats. You have 4 sensors.

You have four O2 sensors, however, you only need two MIL-eliminators, at most, as only the two downstream sensors can make use of them when needed.

Steve