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If your car has a vacuum controlled fuel pressure regulator, it might be worthwhile to check to see that it does not have a bad diaphragm. If it does it would be leaking fuel into the manifold and possibly to the cylinder that is misfiring.
Pull a vacuum on the regulator and see if it holds pressure. It's a simple quick test that might be the problem.
The regulator would be at the point in the fuel rail where the excess fuel is returned to the tank after passing the injectors.
A missing cylinder can increase consumption as well as the additional fuel diluting the oil and causing increases consumption. One quick test if you don't have a vacuum tester is to just smell the oil on the dipstick and see it it has any residual fuel smell to it.
If the vacuum supply hose from the regulator is close to the cylinder that is misfiring it would be evidence that the regulator might have a bad diaphragm. OBD will not pick up a bad vacuum operated pressure regulator, just the resultant symptoms.
My brother had that exact problem with a Chevy truck before 50k miles. The dealer kept resetting the CEL and could not figure out what was wrong. The bad reg was flooding the number 5 cylinder and causing a misfire, and diluting the oil so the engine started using oil at 50 k miles on a truck he bought new.
When we finally figured out what was going on, the oil consumption stopped completely. Not saying that is your case but it might be something worth checking out.
regards
Mech
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