Well Merry Christmas all.
1980 XJ6 4.3l US model.
Now, New tank is in place, and clean clear fuel is flowing.
I hooked a volt meter to the pump connection and put the meter on the trunk so I could see it as I tried to start it.
With the gear shift in D, I turned the key and have 12V in position 3. When I let the key go, I have 0V. ie no power to the pump.
So am I looking at a bad ignition switch or is there some other Lucas wonder that is fouling me up.

Thanks
Bobmo

 

NO.

Pos 3 (Start Position) with the select in D is the "normal " prime trick we all use.

While you hold Start, and have 12 V = mormal, and the pump will run to prime the system.
Release the key, Pos 2, volts goes away, pump stops.

If the pump is running in Pos 3 then all is fine. If it is NOT, and you have the 12v you stated, pump, or pump earth, is AWOL.

All that before any coffee, damn.

 

Very good Grant!
Your on your game first thing in the morning.
So, next silly question, where does the pump get its 12v from after you let go of the key.?
ie in position 2.
Thanks
Bobmo

 

Now its midnight and you ask that, bugga.

Inside the air flow meter, under the black plastic cover, is a contact arm with an apposing arm fixed. the 2 front terminals from memory.

When the engine is cranking, it sucks air, the airfloe flap moves, the arm contacts the other arm, and the fuel ump relay gets woken up, and the fuel pump wakes up, and the Jaguar Gods fire the beast, IF you are blessed.

Thats the simplistic explanation.

Those contacts, sometimes, dont contact, and the pump relay stays dead. Its a systematic, item by item, diagnosis when it goes wrong.

The inertia switch also plays a part here, but that is not still in the grey stuff for a 6 cyl car. The fact you have pump activity in #3 position that Inertia switch is OK.

 

Grant nailed it. I'll just add that there's a diode pack in the circuit to keep all the volts headed in the right direction.

If the pump runs with the key in 'start' then the pump, the relay, inertia switch, and downstream wiring are all OK...as is at least one internal branch of the diode pack.

Remove the air cleaner to expose the front of the Air Flow Meter. You see a spring loaded flap. With the ignition 'on', open the flip with your finger. The fuel pump should run; you'll probably be able to hear it and/or hear gasoline rushing thru the fuel rail.

If not, post back and/or read this:

Fuel Pump Circuit Checklist

Cheers
DD

 

Thanks Guys,
I'm off to see the wizard of Jaguars, and see what happens next,
Grant, feel free to go to sleep.
Bomo

 

I reckon its now a lack of BEER, the fuzzies are taking over.

Sleep is a luxury at the moment, but thanks for the thought.