O2 Sensor Problem?
Over the past few months, gas mileage has dropped from 12 to 9.5. (97 NAS ST, stock 4.0 gas, 61,000 miles.)
Merging into freeway traffic yesterday, was surprised to see black smoke billowing from the exhaust at full throttle.
No CEL. Truck is not overheating. No rattling coming from cats or muffler and no damage to exhaust system. 60,000 mile service done on schedule. Idles fine. Truck seems to drive fine.
After searching the topic here; I am thinking that the run rich condition and reduced mileage may be one or more faulty 02 sensors.
Any thoughts? Any other possibilities? (ie: VSS?)
Thanks very much.