Have you got an exhaust leak?

I have a similar problem.

First off...
I see that you posted this over 6 months ago and that no one has yet
responded. So you may or may not have solved your problem.

I popped in to this group and posted my problem as follows:

----   Posted April 17/04   ------
My car is a 94 Nissan Altima (2.4 litre). What might cause it to consume
huge amounts of fuel? (it uses up 3/4 of a tank on a 20 mile round trip
across town - no traffic - no idling etc.). Other symptoms - runs very
rough with diminished power - produces huge dense clouds of smoke that
smell a bit like gas. This is a somewhat intermittent behaviour. There is a
tiny exhaust leak either at the head/manifold or manifold/exhaust pipe
connection. (the sound is similar to a bad muffler, but originates under
the hood near the motor)

Some suspicions - flakey electrical component (fuel controller?) or flakey
injector.
----   Posted April 17/04   ------

What I have discoverd so far is that exhaust leak cause pressure drop in
the mannifold.  Subsequently, the sensor, there, sends faulty information
to the fuel system which yields an extremely rich fuel supply.

This, some how makes sense to me and I am going to replace the O-ring
gasket at the mannifold/downpipe connection.

It's an inexpensive fix I can do myself.