I have a 1994 Jaguar XJS With the 4.0 Straight 6. I want to put on catless Downpipes / Long Tube Headers. Is there a way to program the ECU so it doesn't have a engine light on? I didn't know if there was a way to reprogram the ECU? I also have a XJR6 I would like to do it to.

 

For the XJR, see XJR Engineers' posts on the X300 forum. He can reprogram the AJ16 ECU's.
https://www.jaguarforums.com/forum/x...emapped-66907/

However, for the earlier AJ6 engines in your XJS, I have never heard of anything like that being offered.