I have a 1993 XJS conv with a 4.0 (6cyl) engine that the check engine light is on and the fault code is ff23. I replaced the oxygen sensor and the light went out. When the engine is run for 15/20 minutes and is hot the check engine light comes on again. This could also mean that the engine is running rich. I cleaned the mass air flow sensor which did not help. I also ran Seafoam cleaner thru the fuel system.Does someone know what else it could be? Car runs great even with the check engine light on and no problems in starting or running. Please help it would be greatly appreciated thanks in advance.

 

Do you have a copy of S91.pdf I uploaded to this site?? Gus also has a copy I sent so it should be on his site also.

The document explains the way the ECM tests/looks for the parameters to set fueling.
There is also a 'Causes' and a testing procedure in the document.

bob

 

Hello, I do not have a copy of this S91.pdf I. Being new to site how would I get a copy to peruse. Thanks