Decreased fuel mileage question

I have a 97 Dodge Dakota that the fuel mileage has went to half of what
I have gotten in the past I have run a code test and nothing has shown
up faulty. Im getting black smoke from the tail pipes which indicates
unburnt fuel . I have replaced the plugs and wires and the air filter is
clean and no obstructions in the air intake hose but the problem still
continues . My normal fuel mileage in the past has been 17-19 mpg hwy
but now it is 10 mpg . My question is there a sensor problem that would
not show up on the code test ? The engine is a 3.9 and auto trans . Any
help on this matter I would greatly appreciate.

On Thu, 10 Jul 2008 12:17:59 -0500, LeonTaylor.DeleteThis@webtv.net (Leon Taylor)
wrote:

>I have a 97 Dodge Dakota that the fuel mileage has went to half of what
>I have gotten in the past I have run a code test and nothing has shown
>up faulty. Im getting black smoke from the tail pipes which indicates
>unburnt fuel . I have replaced the plugs and wires and the air filter is
>clean and no obstructions in the air intake hose but the problem still
>continues . My normal fuel mileage in the past has been 17-19 mpg hwy
>but now it is 10 mpg . My question is there a sensor problem that would
>not show up on the code test ? The engine is a 3.9 and auto trans . Any
>help on this matter I would greatly appreciate.

I had a similar problem a few years ago on a different model. All at
once black smoke and the mileage tanked. Took it to a dealer and they
replaced the oxygen sensor and changed the oil, on the chance that all
that extra fuel had diluted it.

New oxygen sensor, smoke gone mileage back up. I didn't check for any
codes nor did I get a check engine light, just a black smoke cloud.

Jerry O.