1999 XJR. When ignition is turned to the "on" position where it activates fuel pump for one second to build pressure before cranking, is it main pump that activates for one second or the secondary? Thanks, Wolf.

 

The main pump is supposed to activate. That being said, if the main pump has malfunctioned the secondary will activate. To test your main pump you can remove the relay for the secondary pump. If the main comes on and builds pressure your ok. If not then you have been starting on the secondary and the main is bad.
Just a suggestion, if the main is bad and you have to go after it replace both while you are there.

 

Specific to the XJR, the pre-crank pump activation is the secondary pump.

Running below 3500 rpm is the primary, and above 3500 rpm both.

That is the normal operation. If there is a fault detected at the relay level, the
system switches over to operating on the remaining good relay. The system
cannot detect a fault beyond the relay coil. Puling a relay is the "get home"
strategy and nothing more. If both relays are good and present, the car
will happily try to run on a dead pump.

If one pump fails, the other is not far behind. As in hours or days,
not weeks.

I now have the two pumps wired so I can select which pump serves which
function. Whenever I remember, I reverse the function assignment so that
they each get some exercise.

 

Can someone post a photo, other diagram or description of where the two XJR fuel pump relays are located exactly, and which relay is primary and secondary pump?

 

The pump relay locations are in the FRONT MATTERS section of the electrical guide for your particular model.

Look in the RELAY LOCATIONS page.

Use the FIGURES section for actual wiring.

bob gauff

 

I solved my issues. After digging I found that someone had altered the feed from the CPU to the primary pump relay to instead activate the secondary pump relay when cranking and running. Once corrected it of course now reveals the reason, that being the primary pump is bad. Running on the secondary pump worked. I noticed it not get the initial 2 second burst with ignition on, but when cranking the pressure came right up, and car always started mostly normal. But the sloppy wiring job was like a high school kid did it on his first beer. It was a wire that finally fell off and shut it down. How it ran for this long is a miracle. Going to take tank out and change pumps. Thanks for the help, Wolfe.