Jaguar 1993 check engine code FF-23

That is a code for a faulty oxygen sensor reading by the computer. It doesn't always mean the O2 sensor is bad however, it can be in the wiring/ground/connector. You'll have to test the voltage from the sensor. It should be between 1-4 volts with the engine warmed up.

The fuel smell could be from a leaking fuel pressure regulator or line. You'll need to check that. Fuel pressure could also be too high. It should read: 34-38 psi with engine warmed up at idle. Pull the vacuum hose at the FPR and psi should increase by 7-10 psi.