Jim, I hear ya, and I agree on the carbon build up on the pistons as a likely possibility. I really didn't think I knew enough info wrt his vehicle to come here and ask questions about the noise yet, that was just a byproduct of my actual question of when and why the knock sensor went away between Æ96 and Æ99 4.0 XJ. Because I had never heard of an EFI vehicle opperating with out one either.

IÆll hit you all back with what I find out, and with what resolves his issue.

<img src="/forums/images/graemlins/cheers.gif" alt="" />

Sean

99 XJ Sport 2 Door, 4.0L, 5 speed, all stock. Daily Driver
79 F150 Standard Cab Short Box, 400ci, NP435, NP205, 35" SSRs