Hi out there.
I have this beautiful white Jag, Sovereign V12 Series 3 (1985).
I have a problem. When I drive the engine suddenly stops! Maybe I have driven 200 meters or maybe 10 Km or maybe it does not stop at all.
I have checked the electrical (distributer checked) and ignition-coils where power is on when it stops). I can only start to guess now where it is in the fuel system! I have checked that the fuel lines ar OK, no bends or so, the fuelpump works fine, where do I start and where do I stop.
Is there any of the other things like the "no return valve" or things like that I should check??
If any of you have any ideas I would love to hear from you. I have my own workshop with lift and everything, so it's easy for me to work on the car.

Many thanks in Advance and have a great day!

Peter L. Thomsen
Nyborg
Denmark.

 

Including a visual inspection of the distributor wires *under* the distributor itslef?




I presume you mean that, when the engine stops, you've verified that the coil is getting power? If so, good. That eliminates the ignition switch




Before jumping to the fuel system have you looked at the wiring at the ignition amplifier, especially the wire with the braided shielding? Also, inside the amplifier is the AC Delco ignition module....which is know to fail in odd ways. Part number D1906

Does the engine re-start easily?

Cheers
DD

 

Hi Dough
Thanks for the fast reply.
I changed the ignition amplifier, and it's still the same. Sometimes it starts immediately sometimes it takes maybe 5 minutes before it starts. When it starts immediately it fires up on all 12 immediately, when it starts after 5 - 6 minutes (or maybe 3-4) it's like not all the cylinders fire up at the same time, it takes a like maybe 5 secs to get all 12 going?
Yes I checked the coil, power is on! I had the ignition chacked with a Jag specialist just before I put it away for the winter (last year) and the plugs were changed and all. He found no problems.
When I start it it fires up imediately on all 12, it's after maybe 500 meters or 5 Kilometers or 10 it happens, just once or twice. Sometimes it does not happen at all (very seldom).

Best regards
Peter

 

Ok, on to fuel system....


On the V12 cars the fuel pump relay is grounded by the ECU. The circuit in the ECI responsible for this is known to give problems. I would jump-wire the fuel pump relay ground wire with an independent ground wire and see if anything changes. On an XJS this is the orange wire....your car is almost certainly the same

Cheers
DD

 

Thanks Dough for the fast reply.
I will check that

Have a great day
Peter.

 

Hi again Dough.
I changed the fuel pump and the filter (I had new of both). Got it all installed and then, no power to the pump when I turn the ignition on. I found a bad fuse (clock did not work) changed it, and the clock works again, but still no power on "+" on the pump. I tried with separate power to the pump (external battery) and did not start. Have had stroboscope light on the coil (main wire to the distributer) and it's blinking away when the starter turns, so I can rule out ignition.
I am stuck now. Could it be a relay or something electrical for the fuel system? When I tested the pump, i get petrol out from the filter, all the way up to the "rail", both before and after the "pressure valve" (one on each side of the rail). I just cant figure out what is wrong??
Hope someone out there has a good idea. I have to drive a young lady tomorrow from the church as it is her "confirmation". It probably wont happen.
Have a great day
Peter.

 

I just came to think about something. There are 4 relays mounted on top of the radiator (right in the middle). The relays are just plugged into sockets. I am not sure which relay is for what? These sockets are mounted on a plate and the relays are just plugged in each socket.
Could I "shorten" some of the pins in the socket so maybe the fuel pump started to work when the ignition is on? I guess that was a way to bypass a faulty relay??
The first relay has pins numer 85 - 86 -87 and 30 as far as I remember. I can't see the pin-numbers on the other realys.

BR
Peter.

 

my 85 XJ was doing something very similar. Sounds the same anyway.
What it ended up being is the flapper inside of the air flow meter was sticking and suffocating itself. I sprayed a little P.B. on it worked it back and forth untill I felt the dragging go away. Back on the road, I've had to do that twice and now I finaly found a replacement so I wont have to do it anymore.May not be the same problem as you but it sounds familiar.

 

V12 EFI doesn't have a flap-type MAF, instead a vacuum line off the inlet manifold goes is connected to the ECU, which has a pressure sensor built in.

It might be worth reading this article to see how it all hangs together: -

LUCAS EFI / AJ6 Engineering