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Pay someone to scan it an look at the fuel trim is the easiest answer. Focus' are usually great on gas. A hint is that when a car is warmed up and running it's in a closed loop and the computer looks at the o2's and the mass airflow sensor to regulate the fuel. You can try driving it with the mass airflow disconnected. You might get a check engine light but probably not. Ford is notorious for not giving up mass airflow codes. If it gets better gas mileage then try cleaning the MAF. Or just try cleaning it. Not with carb or injector cleaner. It has oil in it. Brake clean is the best. Check the spark plugs. They can tell you more than any other simple test. It they're black with soot then too rich is confirmed. Old weak plugs tend to get a real wide gap and a weak spark. The car might run fine but still use way more fuel.

Well...it's probably an emissions issue (despite the fact that you're not getting a check engine light). This is possible because some emissions readiness tests in vehicles require certain conditions be met prior to finding a fault and triggering the check engine light.

In this case if it's that major of an issue you probably have a bad front oxygen sensor (the one before the catalytic converter). Despite the fact that you have no check engine light there will likely be a diagnostic code on your computer once it's scanned. You should be able to smell it but not everyone can pick up on the smell or symptoms with a catalytic converter.

Besides the fact that it is a ford 4 cyclinder running at 103 thousand miles, its most likely your driving if its an automatic tranny than keep your RPMs under 2k and dont gun it, other wise trade it for a 99 chevy cavolier