1998 ford expedition misfire
how many miles on rig ??? if its over 100 k i would have the cat checked to see if it is still working , when they stop working the down stream o2 sensor picks up on it and leans out the vehicle to keep it emmisions compliant this inturn causes loss of power and poor idle (misfire )
all things changed manufactured for this vehicle? the above answer about the o2 sensor makes good sense.
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