This is a very neet and inovative solution Pabllo.
Can you explain how it works and maybe give us a schematic of the instalation and connections?
It could be a great solution for all that have trouble with their ECU’s fuel pump circuit.
Hi, these kind of relays were used quite a lot, at least here in Europe, in electronic injections from early 90’s. The one that I have used has the following pins:
30, 31, 50, 15, 1, 87 and 87b (I only used the 87).
What I did was wire it next to the ECU and give it a 15 posiitve feed and ground from the ECU wiring. The signal from the starter to the 50 pin and the signal from the ignition module to the 1 pin. I cut the orange cable that comes from the 85 pin from the original relay pump and I wired it on the 30 pin of this new relay. The 87 pin I wired to ground. Basically what this relay does is the ecu function of controlling the fuel pump
relay.
There is only one thing that you have to bear in mind. This relay doesn´t activate the fuel pump when you switch the ignition on, it activates it when it is given the starter signal. To be honest I have tried the car many times now and in pretty cold cranks and the engine starts really quick, even tough the car hasn’t been fired in 5 years, you dont’t feel at all the fact that it doesn’t run the fuel pump for a couple of seconds with ignition on.
Let me see if I got it straight:
#15: +12v Ignition
#87: Ground
#50: +12v from Starter - activates the relay when the starter is engaged.
#1: Ignition module signal (which wire?, positive?, shielded wire?)
If #1 looses signal (engine stops) relay turns Off.
#30: to original fuel pump relay #85 - Ground
The relay when energised connects #87 to pin #30.
Brilliant!
And if the lack of priming the fuel pump ever becomes an issue it’s very easy to add a switch or relay.
In conventional electrical schematic naming , 30 is constant power, 31 is ground and 15 is switched power or ignition I believe. Not sure whether 1 and 50 are ignition pulse and start or vice versa.
Using these namings should still function and be more correct.
1 Like
The 50 signal you can get it from a withe cable that goes to the ECU wich gets the 50 signal from the key and 1 signal you get it form a cable that goes to the ECU too, it is the one that comes from the ignition module and acts as rpm signal to the ECU.
And yes, Aristides, you could install another timer relay to do the priming, but as I said I don’t think it is really necessary. My car is running fine like this and I tell you what there are XJ12’s in better shape than this one for sure 
By the way guys, does anyone of you have wiring diagrmas for this exact car? I have been using wiring diagrams from an XJS V12 form that era and it worked fine until now but now I have a problem with the wiring of one of the fuel senders and all the information I have is for cars with just one tank.
For everything having to do with the V12 refer to the XJS chapter.
For everything else the XJ6 is identical.
All the best.
Thank you Aristides, that’s the manual I needed, I had the XJS part only.
I already checked the fuel gauges wiring and it correspondes to the car.
Thanks.