Code fuel 1 would indicate Oxygen sensor. A good information source is the Haynes Manual Jaguar XJ6 1988-94. Good luck.
Code 43 is a problem in the fuel delivery system.
FFS on a 1990 Cougar stands for feedback fuel system.
MAP sensor
As you do not list the code you are reading, it is impossible to answer your question.
In 1990-1994 XJ6 the VCM Code 44 is the code for the O2 sensor, either rich or lean exhaust has been detected and is causing the code to trigger. It could indicate a bad O2 sensor.
If you mean a low fuel light, then NO.
Ignition Amplifier Failure
this code means there is a problem with the fuel level sensor curcuit
I am running low on fuel
fuel injectors
Bank one fuel system rich.
I have a supercharged 1995 Bonneville and this code has come up quite often. It is a Fuel Trim code. Your fuel is either burning rich or lean.