I would imagine a secondary pump failure would trigger a light or would exhibit some noticeable hesitation higher in the rev range. Like I would imagine you do I keep my XJR in excellent mechanical shape and I have the 1.5lb powerhouse upper pulley for improved midrange pull. What made a difference for me was running some Cataclean to clear out the catalytic converter. I've tried it in other nikasil jags with no ill effect so it seems safe. I've tried Techron, Royal Purple fuel cleaner and phew, the Cataclean made a noticeable difference, it is stronger than ever.

 

A failed primary and/or secondary fuel pump won’t register a cel. If either of the FP relays are removed, then it’ll throw a cel. Locate the secondary fp relay in the trunk fuse box, remove the relay, with the key off, put an inline fused jumper wire in the socket “30” to the one directly across from it which I believe is “87a”. Test it in the main fp first to confirm it’s running and then try it in the secondary fp. When I got my 98’ going about 5 years ago, I went out for its maiden voyage around the block. I floored it and it went “okay” but it wasn’t where I thought it should be. I looked at our history on the car and there was no mention of the fp’s having been done. I got 2 new pumps and when I had the old ones out, they were both from 97’. I ohm’d them out and one of them was open circuit which made sense because of the lack of power. No cel on either.

 

Pumps are easy enough to test manually.
I'm curious if my scanner won't activate them.

I'm sure even if all OK now. Only a matter of time before I replace both pumps on both XJRs. The 99 only has 53k but 20 years is 20 years regardless.

. Even if they spin up on a test doesn't mean you're still getting full volume and pressure under load and WOT.
And of course there is always the dreaded sudden pump failure without notice . Nothing more fun than the random no hot restart when you're out somewhere.
So ATB.if you are hinting around that pumps should be a preventative maintenence item I completely agree.
Any pump over 10 years or 100k becomes suspect to me when considering long trips.